Publications

It is well-known that fixed-frequency constant-coupling series–series capacitively compensated inductive wireless power transfer systems (IWPTSs) may be designed to operate with certain load independent voltage gain (LIVG) value within a region defined by loosely coupled transformer (LCT) parameters. Since LCT parameters values are not arbitrarily selectable in practice, the desired LIVG value may reside outside the attainable region. In such a case, utilizing an inductor (rather than capacitor) as one of the series compensation elements allows extending the attainable LIVG values range. Unfortunately, the method may also cause significant increase in reactive transmitting side currents, yielding overrating of inverter transistors, transmitter side LCT coil and compensation elements. As a remedy, this article proposes utilizing an additional capacitor across ac-side rectifier terminals, yielding two novel mixed inductive-capacitive compensation. The proposed topologies are then thoroughly analyzed providing expressions for IWPTS output voltage range and coil-to-coil, followed by compensation components selection and sizing guidelines. It is revealed that despite definite transmitting side components rating reduction, coil-to-coil efficiency is deteriorated in some cases (while improving in others) and corresponding criteria are derived. Analytical findings are accurately supported both by simulations and experiments, demonstrating a reduction of up to 73% in inverter current rms and a maximum efficiency increase of 41% under certain operating conditions.

Sub-resonant frequency (SRF) operation of inductive wireless power transfer systems (IWPTS) allows attaining constant current (CC) output under varying coupling and output voltage conditions while minimizing transmitter volt-ampere (VA) rating. Unfortunately, SRF-operated IWPTS equipped with diode rectifier-based receivers are uncapable of reducing the output current freely below rated value. This drawback prevents their employment in applications where a wide range of output currents is essential (e.g., Li-ion battery charging, characterized by rated constant current output during constant current stage and gradually decreasing current output down to a near-zero value during constant voltage stage). To bridge the gap, this work proposes equipping the IWPTS with a semi-active rectifier (SAR) based receiver and utilizing SRF control of the transmitter in conjunction with phase-shift (PS) control of the receiver to attain full system controllability under different coupling and varying output voltage conditions. Feasibility of the proposed methodology is successfully validated by experiments.

The paper presents theoretical analysis and practical design of 150W, 48VDC-to-200VDC strongly-coupled inductive wireless power transfer link (IWPTL) for a through-glass AC power delivery system into existing wireless-ready sealed industrial glove box. One of the wireless-ready glove box walls comprises pre-installed dual-side identical transmitting and receiving coils (to assure direction-insensitive installation and confusion-proof repair). The load residing within the enclosed compartment requires a 120V, 60Hz AC voltage supply, created by an off-the-shelf buck-topology inverter powered by the proposed IWPTL operating in load-independent output voltage (LIVO) mode without any feedback. It is shown that due to adoption of symmetrical coils and operation under high coupling coefficient, it is impossible to attain the required voltage gain employing classical series (capacitor) – series (capacitor) compensation. Consequently, the recently revealed series (capacitor) – series (inductor) compensation is adopted in order to attain the required voltage gain value. It is further shown that the output voltage of a practical capacitor-inductor compensated IWPTL remains load-dependent even under LIVO frequency operation, yet residing within a certain range defined in the paper. Expression for coil-to-coil efficiency of the proposed arrangement is also established in this work. Functional feasibility of the proposed system is accurately supported by simulations and experiments.

The paper proposes a novel dual-winding active magnetic energy harvester (D-AMEH), clamped around single power line conductor carrying AC currents with time-varying magnitude while supplying a constant power DC load via an uncontrolled rectifier (e.g., 24/7 aerial marker ball lighting). To allow continuous power flow to the load despite intermittent nature of power line current magnitude, an energy storage unit (rechargeable battery) is integrated into the system via an additional secondary winding, creating an AC-coupled, isolated hybrid energy system with completely decoupled battery and load voltages. The D-AMEH simultaneously harvests the maximum power from the current-carrying conductor and feeds the load with constant power, letting the battery to seamlessly match the difference between harvested and consumed power. Analytical expressions for system currents and voltages are developed, followed by conversion losses estimation. The revealed findings are accurately supported by experiments, demonstrating close matching with corresponding analytical predictions.

The letter focuses on clamped-type passive magnetic energy harvester equipped with constant-valued series AC-side capacitor (cCs-MEH), supplying power to a constant voltage load (CVL) representing a battery or regulated DC bus, via diode bridge rectifier. Such an arrangement may serve as, e.g., powertrain of a platform for uninhabited aerial electrical vehicle batteries charging residing in the vicinity of overhead power lines. It was recently shown that series-connected capacitor addition allows to enlarge the harvested power by up to 27% due to decoupling of the load from the voltage applied to transformer core. However, the capacitance value must be adjustable to allow maximum harvested power increase under arbitrary primary current magnitudes, significantly complicating the system and reducing reliability. On the other hand, equipping the MEH with a constant-valued series capacitance seems to be more practical. Yet, harvested power boost is expected to be lower than the above-mentioned amount. This brief aims to bridge the gap by discussing sizing process of series capacitance value and assessing the power harvesting potential of a cCs-MEH driving a CVL within certain range of primary current magnitudes. Such an investigation has not been reported in the literature so far. In addition, it is revealed that a cCs-MEH would be outperformed by an optimally designed series capacitorless MEH (utilizing the same core) under low primary currents. Experimental results of a cCs-MEH clamped on conductor carrying 50–350 A, 50 Hz currents are provided to validate the findings.

The paper proposes a methodology for deriving static control-to-input average power and control-to-output average power characteristics of an active magnetic energy harvester (AMEH) clamped on sinusoidal current-carrying conductor (e.g. overhead power line) while feeding a constant voltage type load (e.g. uninhabited aerial vehicle battery). Transfer window opening instant serves as the control variable while corresponding closing instant is imposed by AMEH parameters to impose full magnetic core utilization. Analytical expressions for average power harvested by the AMEH from a current-carrying conductor are derived first within feasible range of control input variable values. Then, corresponding conversion losses are assessed to estimate the amount of average power provided by the AMEH to a load. It is revealed that control-to-output power characteristic is non-monotonical for a given value of primary current magnitude, possessing a single maxima. Finally, the paper demonstrates that the output average AMEH power may be smoothly regulated between zero and the maximum level only within a limited region of control input variable values. Presented analytical findings are accurately supported by experimental results of an AMEH clamped on a conductor carrying 100A – 300A, 50Hz currents (typical for medium voltage power line).

Magnetic energy harvester clamped on high-ac-currents-carrying conductor (e.g., split phase of an overhead power line) may serve as a part of an uninhabited aerial electrical vehicle battery charging platform. The brief reveals analytical expression for the power delivered to a constant voltage type load (e.g., battery or regulated dc bus) by an active magnetic energy harvester (AMEH) operated under transfer-window-alignment control for determining the optimal (in terms of load power maximization) number of secondary winding turns (N). It has been recently demonstrated that for a given core, the power harvested by an AMEH from a current-carrying conductor increases monotonically when N is reduced. On the other hand, it is discovered that AMEH conversion losses are concurrently increased. As a result, the power supplied by an AMEH to the load is a nonmonotonic function of secondary winding turns number, attaining a global maxima for certain unique value of N. Analytical expression allowing to obtain the optimal secondary winding turns number is developed in the letter and validated experimentally by application to an AMEH clamped on 200 A, 50 Hz current carrying conductor while driving a 45 V constant voltage load (emulating 12s Li-Ion battery).

The letter discusses the performance of clamped-type active magnetic energy harvester (MEH), supplying power to a constant-voltage-type load via transfer-window-alignment controlled rectifier. Presented analysis investigates practical harvesting potential of active MEH operating under high primary currents and compares it to that of a passive (uncontrolled rectifier equipped) MEH. It is revealed that harvested active MEH power may be increased for a given core by reducing the number of secondary conductor turns N, yet it is accompanied with escalated current ratings of secondary conductor and rectifier components. Theoretical harvesting potential of active MEH is shown to be ∼38% higher than that of an optimally designed passive MEH utilizing the same magnetic core under similar operating conditions (i.e. primary current magnitude and load voltage). However, somewhat lower figure of merit should be expected in practice since N cannot be reduced to zero. Experimental results of active MEH harvesting ∼285 W (which is ∼95% of the theoretical upper harvested power bound) from a conductor carrying 300ARMS at 50Hz validate the revealed findings.

The paper concerns designing a passive (i.e. employing an uncontrolled rectifier) magnetic energy harvester (MEH) clamped on a high-AC-currents-carrying conductor, aimed to power rechargeable batteries under maximum allowed charging current constraint. Such a system may serve as e.g. a part of platform residing on a split phase of an overhead power line for uninhabited aerial electrical vehicle batteries charging. It has been recently shown that a passive MEH may be optimally matched (in terms of harvested power amount) to a given constant voltage load (CVL) by appropriate selection of core cross-sectional area and secondary conductor turns number. However, battery terminal voltage does not remain constant but undergoes significant increase during charging process. Hence, MEH power averaged over the range of voltage values expected during charging cycle should be maximized in such a case. Corresponding simplified design guidelines are derived and verified by both simulations and experiments. The guidelines are used to design a MEH capable of charging a 44.4 V, 10 Ah Li-Ion battery with nearly constant power of ∼115 W when clamped on a conductor carrying 200 A current while complying with 3 A maximum charging current constraint. It is revealed that due to relatively low sensitivity of output passive MEH power-voltage characteristic around corresponding maximum power point, average charging power remains within the range of 2% of the maximum device yield while battery terminal voltage undergoes 31.25% variation.

The paper concerns passive magnetic energy harvesters (PMEHs) employed to supply low-voltage (typically DC) loads from high AC current carrying conductors (e.g., drone battery charging platform residing on a split phase of an overhead power line). It was recently shown that unique load voltage value maximizes harvested device power irrespectively of primary current magnitude assuming sufficiently low magnetizing current of PMEH transformer core. Corresponding simplified design guidelines were derived, allowing to optimally match a PMEH to a constant-voltage-type load (CVL) by proper selection of transformer core cross-sectional area and number of secondary winding turns. However, disregarding core magnetizing current may not be accurate in practice even under high primary currents due to utilization of gapped core, required for PMEH clamping on/off an existing power line. This paper aims to assess actual performance of a clamped-on PMEH designed to drive a certain CVL using above-mentioned simplified guidelines under wide range of primary current magnitudes. It is revealed that the loci of harvested PMEH power deviates noticeably from corresponding maximum power line (MPL). However, harvested power difference is negligible due to low sensitivity of power-voltage PMEH characteristics in the vicinity of MPL. Presented findings are accurately supported by experimental results of a PMEH sized (using simplified design guidelines) to harvest 220W from a conductor carrying 300ARMS current while supplying a 45V CVL.

This article provides a methodology for deriving a family of output characteristics (dc-side I–V and P–V curves) for a passive magnetic energy harvester (MEH) clamped on a sinusoidal current-carrying conductor. It is demonstrated that MEH characteristics depend on primary current magnitude and frequency as well as on load voltage. First, expressions for power harvested by an MEH are derived employing a nonlinear B–H curve approximation of the core. Then, conversion losses are assessed to provide respective estimates for the power provided by the MEH to the load. Presented analytical findings are accurately supported by experimental results of MEH designed to harvest up to 240 W from a conductor carrying currents of up to 350 A.

This article provides a methodology for deriving a family of output characteristics (dc-side I–V and P–V curves) for a passive magnetic energy harvester (MEH) clamped on a sinusoidal current-carrying conductor. It is demonstrated that MEH characteristics depend on primary current magnitude and frequency as well as on load voltage. First, expressions for power harvested by an MEH are derived employing a nonlinear B–H curve approximation of the core. Then, conversion losses are assessed to provide respective estimates for the power provided by the MEH to the load. Presented analytical findings are accurately supported by experimental results of MEH designed to harvest up to 240 W from a conductor carrying currents of up to 350 A.

In the article “An Effective Power Improving Method of Magnetic Field Energy Harvesters Using a Series-Connected Capacitor for Wireless Sensors in Smart Grids” by Li et al. (2024), the enhancement of magnetic energy harvester (MEH) performance by adding a series-connected capacitor was discussed. It was shown that the optimal (in terms of harvested MEH power) capacitance value is inversely proportional to the load resistance value. Yet, some functional properties could have been missed out due to the adoption of a high-permeability ungapped core (without calling into doubt the validity of presented results). Moreover, optimal transfer window length was not obtained. Consequently, the purpose of this comment is twofold: demonstrating some operational details not highlighted in Li et al. (2024) and complementing them by providing analytical expressions for optimal transfer window length and corresponding harvesting potential of the MEH. Experimental results validate the complementary comments.

Due to the practical current source characteristics of a passive magnetic energy harvester, it may be conveniently interfaced by either voltage-type or resistance-type load. The load type preferable for interfacing an energy source is the one possessing the narrowest range of values belonging to the maximum power line (a curve linking all possible maximum power point coordinates of power source output characteristics). The brief adopts a set of recently developed equations to compare output characteristics (power–voltage and power–resistance) of a passive magnetic energy harvester and corresponding maximum power lines under a wide range of primary currents. It is clearly shown that voltage-type load should be preferred over resistance-type load for passive magnetic energy harvester interfacing. The findings are supported by experimental results of a passive magnetic energy harvester operating under primary currents of 50–350 A.

The brief presents a method for deriving a type-II voltage controller coefficients set allowing to minimize the dc link capacitance in single-phase active power factor correction rectifiers (PFCR) operating without hold-up time requirements. The proposed methodology considers grid current quality and dc link voltage loop stability constraints as well as system response to a step-like zero-to-rated load power variation. Design guidelines for deriving the optimal coefficients set and corresponding minimum capacitance value are provided by means of combined time and frequency domain analysis. The findings are accurately supported by simulations and experiments.

Type-II and proportional–integrative (PI) compensators are often employed as dc-link voltage controllers in practical single-phase power factor correction rectifiers (PFCRs). The corresponding controller coefficients are typically designed in frequency domain according to a rule-of-thumb imposing crossover frequency around 10 Hz, yielding unnecessarily high (>45°) phase margin (PM). Recently, analytical guidelines for deriving PI controller coefficients set, allowing the system to comply with grid current total harmonic distortion (THD) and dc link voltage loop PM constraints, were established. This article demonstrates that an additional degree-of-freedom (DOF) present in type-II compensator (compared to PI) permits optimizing dc-link voltage response to load step in addition to the abovementioned constraints fulfillment. Design guidelines for deriving optimal type-II compensator coefficients set by means of combined time and frequency-domain analysis are provided. The revealed findings are accurately supported by simulations and experiments.

In many practical applications, such as electric vehicle charging and smart transformers, reverse power flow is significantly lower than forward power flow. Designing a full-rated bidirectional DC/DC converter in such cases leads to increased hardware costs. To address this, recent research has explored isolated topologies that support asymmetrical bidirectional power flow at reduced cost. This manuscript investigates an asymmetrical bidirectional DC/DC (AB-DC/DC) converter that integrates a partial-scale active bridge and a partial-scale diode bridge connected in parallel on the secondary side. Passive power sharing between these bridges is controlled by selecting appropriate coupling inductors, but practical magnetic tolerances cause power imbalances. To mitigate this, a novel modulation technique is proposed to enable active power sharing, allowing power transfer from the diode bridge to the active bridge. The study covers various operating regions, including discontinuous conduction mode (DCM), continuous conduction mode (CCM), dual-active-bridge (DAB) mode, and two hybrid regions, where the diode bridge operates in DCM and the active bridge in CCM. Closed-form power expressions and boundary conditions are derived for all modes. The proposed strategy is validated through simulations and experimental measurements on a hardware prototype, demonstrating consistent waveform behavior and confirming the feasibility of active power transfer from the diode bridge to the active bridge.

Second-order notch filters (NFs) with constant coefficients are often used as part of feedback controllers in grid-connected power conversion systems to prevent unwanted harmonic content polluting the closed control loops. In practice, the value of the mains frequency resides within a certain known range rather than remaining constant. Hence, the correct selection of NF coefficients is crucial for ensuring that the desired performance is maintained within the whole expected mains frequency range. Bilinear transformation (BLT) with notch frequency prewarping is often adopted to convert an NF from a continuous to a digital form. While accurately preserving the notch frequency location, the method reduces the filter bandwidth. As a remedy, BLT with both notch frequency and damping ratio prewarping may be employed. Nevertheless, some inaccuracy remains under low sampling-to-notch frequency ratios. This technical note demonstrates that the issue may be solved by prewarping the boundary values of the expected harmonic frequency range rather than the notch frequency and/or damping factor before applying the BLT. Simulation results accurately support the presented issue and proposed solution.

Capacitor-powered resonant inverters are often employed in pulsed-power applications to feed an equivalent series resistance–inductance–capacitance (RLC) load with time-varying component values. Establishing the short-time dynamics of such an arrangement is nontrivial since the system does not reach a steady state within a single pulse period. As a result, linearization around a single operation point cannot be applied for the sake of simplified system modeling. Consequently, the design of feedback controllers for such systems (aiming for, e.g., resonant frequency tracking or energy transfer rate regulation) is highly cumbersome and challenging since a linear time-invariant regulator is unable to bring the system to desired performance within the whole expected operation range. To cope with the modeling task, a reduced-order envelope model of a capacitor-fed resonant inverter feeding a time-varying RLC load was recently proposed by the authors. In this paper, this model is further simplified and split into linear and nonlinear parts, allowing the employment of a combination of feedback linearizing (nonlinear) action with a linear time-invariant regulator to form a nonlinear control structure allowing the attainment of resonant frequency tracking within a wide operation range. The proposed controller design methodology is accurately validated by multiple time-domain simulations.

The letter concerns clamped-type magnetic energy harvesters (MEH), supplying power to constant voltage (CV) loads via a diode rectifier. Presented analysis suggests that if primary current magnitude reflected to the secondary side is much higher than core saturation current, then optimal (in terms input MEH power maximization) transfer window length and corresponding load voltage-per-turn ratio become independent of primary current. As a result, certain unique value of load voltage maximizes the power of a given MEH irrespective of primary current magnitude. Moreover, mean magnetic flux path length, B–H curve shape and permeability of the core have no effect on either optimal load voltage-per-turn ratio or maximum harvested power under the above circumstances. Experimental results of MEH capable of harvesting 173 W from a conductor carrying 250 Arms validate the revealed findings.

The letter concerns a clamped-type passive magnetic energy harvester (MEH), supplying power to a general load via a diode bridge rectifier (DBR). It is known that a certain value of output MEH voltage (referred to as optimal) maximizes harvested power. Under high primary current magnitudes, the optimal voltage value is constant, i.e., current-independent. Consequently, it was recently proposed to interface a passive MEH to a general load via a switching power converter whose input (i.e., MEH-side) voltage is regulated to a corresponding constant voltage reference, realizing the maximum power point reaching (MPPR) method. However, optimal voltage value becomes current-dependent under low primary current magnitudes. As a result, the power harvested by MPPR-operated MEH becomes suboptimal if the MEH-side voltage reference of the converter remains unchanged. Hence, the brief suggests allowing the converter input voltage reference value to be adjusted (by, e.g., a maximum power point tracking loop) to maximize harvested MEH power under low primary currents as well. Experimental results comparing the harvested power of a passive MEH under classical and enhanced MPPR methods validate the proposed enhancement.

Series-stacked buffer (SSB)-based active dc links aim to increase power density by replacing bulky dc link capacitor with series connection of significantly lower valued capacitor and auxiliary bidirectional dc/ac converter. SSB design constraint describing quantitative relation between passive components values and system power rating was established to achieve minimal remaining dc link voltage ripple magnitude. This letter generalizes the above requirement, revealing that allowing nonminimum magnitude of residual dc link voltage ripple releases other design constraints, yielding a more optimal solution in terms of full-rating capacitance utilized and/or auxiliary bidirectional dc/ac converter volt-ampere rating. Experimental results validate the proposed methodology, matching corresponding analytical predictions.

Frequency control of series-series compensated inductive power transfer links (SS-IWPTL) operated in sub-resonant region while feeding variable voltage-type loads (e.g. batteries) with constant current under uncertain coupling conditions allows to minimize volt-ampere (VA) rating of transmitting-side converter. In such systems, variations of coupling coefficient and load voltage are counteracted by operational frequency adjustment so that primary current magnitude remains nearly unchanged throughout the complete operational range, as opposed to input voltage and phase shift control approaches. In practice, allowable operational frequency band is typically restricted by certain application and/or standard (e.g. SAE J2954). As a result, tolerable load voltage span and coupling coefficients range are also limited. Classical design guidelines impose the resonant frequency of SS-IWPTL to coincide with the upper bound of allowable operational frequency band for operation with the minimum expected coupling coefficient and the lower bound corresponding to operation with the maximum expected coupling coefficient. The paper demonstrates that generalizing this approach by releasing the former constraint adds a degree of freedom, allowing to expand tolerable coupling coefficients range for a given operational frequency band at the expense of slight efficiency deterioration. Analytical relations describing the above-mentioned behavior are established, clearly indicating the arising trade-offs. Simulation and experiments validate the proposed methodology.

It is well-known that series(capacitive)-series(capacitive) compensated inductive wireless power transfer links (SS(CC)-IWPTL) operating at fixed frequency with constant coupling coefficient may be designed to attain arbitrary load independent voltage gain (LIVG) value, residing within a region defined only by loosely coupled transformer (LCT) parameters. Such a characteristic allows designing the system to be sensorless and operate without feedback, which is an extremely useful feature in hostile environment applications. Unfortunately, LCT parameters are not selected arbitrarily in practice; hence, the desired LIVG value may reside outside the attainable region, calling for an additional power conversion stage. In particular, region of attainable LIVG values is especially narrow when LCT inductances ratio is imposed by the application and thus cannot be freely selected. One of existing challenges is regulating the system output to low DC voltage while it is being fed from a much higher valued voltage source, i.e. calling for an extremely low LIVG value. The paper demonstrates that adopting an inductor rather than a capacitor as primary series compensation element allows to extend the lower bound of attainable LIVG values region for given LCT and operating frequency, potentially eliminating the need for an additional step-down power converter. Resulting coil-to-coil efficiency is quantified and guidelines for sizing corresponding compensation elements pair are established as well. Simulations and experiments accurately verify the proposed methodology.

Wireless power transfer systems are typically required to operate under varying geometrical positioning (vertical distance, misalignment) between the transmitter and receiver coils while supporting a load with non-constant characteristics. This creates the need for robust systems that can operate over a range of coupling coefficients under time-varying load. Widespread control methods utilized to support such an operation typically suffer from volt-ampere (VA) over-rating of the inductive wireless power transfer link (IWPTL) transmitter. Sub-resonant frequency control has proven to be an effective solution to this problem, attaining robust operation and minimized transmitter VA rating by utilizing operational frequency as the control variable for system output regulation under above-mentioned constraints. However, allowed operating frequency range is usually restricted in practical applications (e.g. to 79 kHz–90 kHz by SAE J2954 EV charging standard), limiting the misalignment tolerance of sub-resonant control method. Recently, extension of the classical sub-resonant control methodology was proposed in order to overcome this limitation. However, no clear guidelines were given for designing practical IWPTLs operating under extended sub-resonant control. To this end, this work bridges the gap between academical findings and practical applications by establishing generalized guidelines for designing sub-resonant controlled series-series (SS) compensated IWPTL with minimized transmitter VA rating, allowing to maximize misalignment tolerance under given operating frequency and output voltage ranges. The proposed methodology is accurately validated by simulations and experiments, demonstrate close correlation with analytical predictions. Experimental framework reveals that IWPTL operating under extended sub-resonant control methodology attains 50 % increase of tolerable coupling coefficients range compared to a classical system designed to operate under sub-resonant control under identical operating conditions while achieving nearly similar DC-to-DC efficiency.

Recently, much attention has been given to the development of various energy harvesting technologies to power remote electronic sensors, data loggers, and communicators that can be installed on smart grid systems. Magnetic energy harvesting is, perhaps, the most straightforward way to capture a significant amount of power from a current-carrying overhead line. Since the harvester is expected to have a small size, the high currents of the distribution system easily saturate its magnetic core. As a result, the operation of the magnetic harvester is highly nonlinear and makes precise analytical modeling difficult. The operation of an overhead line magnetic energy harvester (OLMEH) generating significant DC power output into a constant voltage load was investigated in this paper. The analysis method was based on the Froelich equation to analytically model the nonlinearity of the core’s BH characteristic. The main findings of this piecewise nonlinear analysis include a closed-form solution that accounts for both the core and rectifiers’ nonlinearities and provides an accurate prediction of OLMEH transfer window length, output current, and harvested power. Continuous and discontinuous operational modes are identified and the mode transition boundary is obtained quantitatively. The theoretical investigation was concluded by comparison with a computer simulation and also verified by the experimental results of a laboratory prototype harvester. A good agreement was found.

Recently, there has been a significant focus on developing various energy harvesting technologies to power remote electronic sensors, data loggers, and communication devices for smart grid systems. Among these technologies, magnetic energy harvesting stands out as one straightforward method to extract substantial power from current-carrying overhead lines. Due to the relatively small size of the harvester, the high currents in the distribution system quickly saturate its magnetic core. Consequently, the magnetic harvester operates in a highly nonlinear manner. The nonlinear nature of the downstream AC to DC converters further complicates the process, making precise analytical modeling a challenging task. In this paper, a clamped type overhead line magnetic energy harvester with a controlled active rectifier generating significant DC output power is investigated. A piecewise nonlinear analytical model of the magnetic harvester is derived and reported. The modeling approach is based on the application of the Froelich equation. The chosen approximation method allowed for a complete piecewise nonlinear analytical treatise of the harvester’s behavior. The main findings of this study include a closed-form solution that accounts for both the core and rectifiers’ nonlinearities and provides an accurate quantitative prediction of the harvester’s key parameters such as the transfer window width, optimal pulse location, average DC output current, and average output power. To facilitate the study, a nonlinear model of the core was developed in simulation software, based on parameters extracted from core experimental data. Furthermore, theoretical predictions were verified through comparison with a computer simulation and experimental results of a laboratory prototype harvester. Good agreement between the theoretical, simulation, and experimental results was found.

The restructuring of the power grid calls for various energy harvesting technologies to power prospective remote electronic sensors, data loggers, and communication devices that could be installed at locations with restricted access. Magnetic energy harvesting stands out as a promising technology that is well suited for such applications while also being able to provide a significant amount of power. In this paper, a clamped-type overhead line magnetic energy harvester in configuration with passive and active rectifiers loaded with a constant voltage load is investigated. Here, an approximate piecewise linear model of the magnetic core is applied to represent the operation of the joint harvester–rectifier system. The main findings of this study include design-oriented analysis that easily lends itself to engineering applications. Based on the proposed analytical results, design guidelines are suggested to establish the key parameters of the harvester’s magnetic structure such as core size and number of secondary turns. Design examples are presented and verified using both simulation and experimental results. A good agreement of the results was found. The offered approach is simple and suitable for engineering purposes.

Electronic capacitor (EC) is a circuit typically aimed to replace (in part or entirely) the bulk DC-link capacitor of a grid-interfacing power converter in a plug-and-play manner. EC is realized by a bidirectional dc-dc converter terminated with small auxiliary capacitor. The converter is controlled such that its DC-link side terminals mimic the behavior of a capacitor with much higher constant capacitance. In this article, a modification of the classical EC control structure is proposed, imposing the DC-link side terminals to emulate a frequency-variant capacitor rather than a constant one. The proposed algorithm allows achieving simultaneous reduction of both DC-link voltage ripple and grid-side current total harmonic distortion (THD) compared to ones attained by classical solutions, thus improving the tradeoff between DC-link voltage dynamics and ac-side current quality inevitably present in any grid-connected power converter. The proposed methodology is well supported by experiments.

This paper presents an extension of a 5-level T-Type inverter to a high-power multi-level inverter that can be implemented in electric vehicles and trucks. The proposed inverter possesses several advantages over standard topologies such as Neutral Point Clamped, Flying Capacitor, and Cascaded H-bridge. The main advantages are a low number of components, an estimated lower price and weight, smaller dimensions, and the implementation of only one DC voltage source per phase. The proposed topology can be implemented for any required odd number of voltage levels. Due to the estimated reduced dimensions and weight, the proposed topology is especially suitable for electric transportation applications. The operation of the proposed topology was validated for 9- and 13-level configurations under PD, POD, and APOD PWMs. The simulation results show the inverter’s practicability for supplying motors of electric trucks.

Three-phase three-level AC/DC and DC/AC converters have demonstrated several advantages over their classical two-level counterparts such as better efficiency, enhanced total harmonic distortion, lower dv/dt and lesser overall chip area. T-type and neutral point clamped (NPC) topologies dominate the family of three-phase three-level converters, widely used in 10kVA – 100kVA power range. However, control of three-level converters is more complicated than of their classical two-level counterparts due to necessity of adopting an additional voltage loop, aimed to balance partial split DC link voltages. Moreover, the latter contain multiples of triple-base-frequency harmonic ripple even under balanced AC-side operation (this does not happen in two-level converters), which should be minimized by the balancing loop mentioned above. The nature of partial DC link ripple formation was analyzed in-depth for unity power factor operation, yet hardly extended to non-unity power factor cases. Moreover, inaccurate conclusions were drawn in some of the related studies. Consequently, this paper focuses on comprehensive modeling and formulation of split DC link capacitors balancing problem in three-phase three-level bidirectional AC/DC converters operating with arbitrary power factor. Analytical expression for dynamics of partial DC link voltages difference is derived and studied in depth. The relation between zero-sequence component of modulation signals and neutral point current, tending to unbalance partial DC link voltages is explicitly established for arbitrary power factor values. Practical cases of restricted and unrestricted zero-sequence component of modulation signals are presented. Analytical predictions are shown to be fully supported by simulations based on both switching-cycle-averaged and full switched converter models. Experimental results obtained employing a 10kVA T-type converter prototype operating with restricted zero-sequence component of modulation signals under different power factor values are also given to further validate the presented methodology.

Asymmetric multilevel inverters (MLIs) with unequal voltage steps (UVSs) are often combined with the staircase modulation (SCM) technique to improve both voltage and current total harmonic distortion (THD)– an approach known as optimal minimization of THD (OMTHD). This is usually achieved by varying both the switching angles (SAs) and the dc source ratios (DCR), to obtain the desired modulation index (MI) while THD is minimized. In this article, a novel sine pulsewidth modulation (SPWM) based OMTHD is considered as an alternative to SCM-based OMTHD. Because only the DCRs need to be optimized instead of both SAs and DCRs, the OMTHD process is simplified, while voltage THD, current THD, as well as power efficiency, are improved, especially for the medium-low MI range, compared to conventional SPWM. An analytical formulation of phase-voltage THD for UVS-based SPWM MLIs is derived and utilized for the novel SPWM-based OMTHD. Validation is carried out by theoretical analysis, digital simulations, and real-time controller + Hardware-in-Loop (C-HIL)-based experiments.

In the paper by Barbi (2021), the concept of series loss-free resistor (SLFR) was presented. The SLFR was realized by novel circuitry derived by topological variation of classical noninverting buck–boost converter operated in discontinuous-conduction mode. The purpose of this note is complementing the work of Barbi (2021) by demonstrating that SLFR may also be realized by classical converters employing dedicated current loops. Validation is carried out by realizing the capacitors balancer example by Barbi (2021) by means of a classical noninverting buck–boost converter, demonstrating the results similarity.

This article presents a generic approach to load-current THD minimization in hard-switched Staircase Modulation (SCM) based three-phase (3ɸ) Multilevel Inverters (MLI) with either fixed or variable DC source Ratios (DCR). First, a computer-aided closed-form analytical formulation of Weighted THD (WTHD) applied directly to line-voltage waveforms is derived using Maple software and then verified against numerically-obtained results of previous works. The proposed symbolic analysis of Weighted Line-voltage THD (WLTHD) applies to 3ɸ-MLIs of any topology with Equal Voltage Steps (EVS) or Unequal Voltage Steps (UVS), and any number of voltage levels count (N), either odd or even. Such an analytical approach eliminates the risk of underestimation errors associated with numerical methods. The proposed closed-form WLTHD expression is then utilized for optimal minimization of current-THD in 3ɸ inductive loads with unconnected neutral. This is achieved by introducing a generic UVS-based Optimal Minimization of WLTHD (OMWLTHD), which calculates the optimum Phase Switching Angles (PSA) and the supply DC-Ratios (DCR), given any desired Modulation Index (MI), thus ensuring minimum current-THD across the entire linear MI range. The revealed OMWLTHD approach is fully validated by both digital simulations and controller plus hardware-in-loop (C-HIL) based experiments, using 7-, 8-, and even 13-level 3ɸ-MLIs of both EVS and UVS configurations. Furthermore, to reveal the impact of WLTHD minimization on actual load current-THD, the MLIs were loaded by a Resistive-Inductive-EMF (RLE) load, as well as a 3ɸ squirrel cage induction motor, thus representing a wide range of possible loads, such as motors and ac grids. The conclusive verification results have shown that in the case of 3-wire inductive loads with a power factor up to 0.95, the proposed UVS-based WLTHD optimization is more beneficial for current-THD minimization over other harmonic distortion quantifying parameters, as WLTHD presents the strongest correlation to actual load current THD when tested against any other parameter such as phase and line THD or WTHD. The revealed improvement in current THD was even more pronounced for UVS-based SCM compared to traditional EVS-based SCM. Additionally, MATLAB and Maple source files of the proposed WLTHD formulations and Excel-based pre-calculated optimum PSA and DCR sets for different values of N are provided as downloadable links to further enhance the contribution of the article.

It is well-known that series–series-compensated resonant inductive wireless power transfer links (SS-IWPTL) may be designed to attain load-independent voltage output (for given operating frequency and coupling coefficient. Unfortunately, the corresponding inverter output impedance is either highly inductive or highly capacitive (inductive region is typically preferred due to natural zero-voltage switching of inverter transistors), significantly increasing inverter volt-ampere (VA) rating. The letter demonstrates that designing the SS-IWPTL for operation in the capacitive region and then adding a shunt inductor across ac-side terminals of either inverter or rectifier allow attaining inverter zero-phase angle, thus minimizing its VA rating.

It is well-known that adding a notch filter in series with the typically employed type-II (or PI) regulator allows improving the tradeoff between dc-link voltage dynamics and grid-side current total harmonic distortion (THD) in practical single-phase power factor correction rectifiers. The article demonstrates that notch filter utilization alternatively allows reducing the value of dc-link capacitance in case hold-up time requirement is absent. The revealed value of minimum capacitance is expressed by explicit function of possible mains frequency values range, maximum expected grid voltage magnitude, rated system power, dc-link voltage set point, maximum tolerable grid-side current THD, and the desired phase margin (PM) of dc-link voltage loop. It is demonstrated that the proposed approach yields fourfold reduction of dc-link capacitance for typical values of 5% tolerable grid-side current THD under 40° PM constraint. Experimental results exhibit close-fitting resemblance to corresponding analytical predictions, verifying the proposed methodology.

This paper reviews different types of capacitors and auxiliary source circuit topologies and presents an introduction to control strategies used for circuit applications reducing DC-BUS capacitance. The paper argues in favor of replacing bulky electrolytic capacitors in capacitor-supported power electronic systems with auxiliary source circuits. DC-BUS capacitors are widely used in grid-tied power converters (rectifiers) and utilized for power balance, voltage ripple limitation, and short-term energy storage. The electrolyte capacitor is the Achilles heel of any rectifier and power converter due to its higher rate of failure than other circuitry components. Auxiliary source circuits are key components to qualitatively improve the reliability of the DC links, where they divert the instantaneous pulsating power into extra reliable storage components. Unlike previous work, this review serves to provide a clear picture of an auxiliary source circuit design, in favor of optimal solution selection according to the specific application. Therefore, energy storage components (capacitors), topologies, and control strategies of auxiliary source circuits are comprehensively reviewed in this paper. Additionally, detailed explanations, comparisons, and discussions of auxiliary source circuits are offered.

This paper introduces an approach to calculating the minimum value of split DC link capacitance in three-phase three-level grid-connected DC-AC converters operating with unity power factor without either active balancing circuits or AC zero sequence injection. Due to the fact that partial DC link voltages and rectified mains phase voltages reach their maximum and minimum values, respectively, at different time instants, it is feasible to decrease the minimum value of the former below the maximum value of the latter while still maintaining proper functionality of the power stage. The minimum possible split DC link capacitance values are hence derived from the boundary condition where the above-mentioned voltages are tangent to each other. The accuracy of the analytical derivations is confirmed by simulations and experiments carried out on a 10 kVA T-type converter prototype, which show a high degree of agreement.

Statistical characteristics of the wind speed in the Samaria region of Israel have been analyzed by processing 11 years of wind data provided by the Israeli Meteorological Service, recorded at a 10 m height above the ground. The cumulative mean wind speed at a measurement height was shown to be 4.53 m/s with a standard deviation of 2.32 m/s. The prevailing wind direction was shown to be characterized by a cumulative mean azimuth of 226° with a standard deviation of 79.76°. The results were extrapolated to a 70 m height in order to estimate wind characteristics at the hub height of a medium-scale wind turbine. Moreover, Weibull distribution parameters were calculated annually, monthly, and seasonally, demonstrating a good match with histogram-based statistical representations. The shape parameter of the Weibull distribution was shown to reside within a narrow range of 1.93 to 2.15, allowing us to assume a Rayleigh distribution, thus simplifying wind turbine energy yield calculations. The novelty of the current paper is related to gathering wind statistics for a certain area (Samaria), and we are not aware of any published statistics regarding wind velocity and direction in this area. These data may be interesting for potential regional wind energy development in which the obtained Weibull distribution could be used in calculations for the expected power generation of particular turbines with a known power dependence on velocity. We have given an example of these calculations for three different types of turbines and obtained their yield in terms of electric power and economic value. We also point out that the fact that realistic wind velocity statistics can be described well by an analytic formula (Weibull distribution) is not trivial, and in fact, the fit may have been poor.

Asymmetric multilevel inverters (MLIs) with unequal voltage steps (UVSs) are often combined with the staircase modulation (SCM) technique to improve both voltage and current total harmonic distortion (THD)– an approach known as optimal minimization of THD (OMTHD). This is usually achieved by varying both the switching angles (SAs) and the dc source ratios (DCR), to obtain the desired modulation index (MI) while THD is minimized. In this article, a novel sine pulsewidth modulation (SPWM) based OMTHD is considered as an alternative to SCM-based OMTHD. Because only the DCRs need to be optimized instead of both SAs and DCRs, the OMTHD process is simplified, while voltage THD, current THD, as well as power efficiency, are improved, especially for the medium-low MI range, compared to conventional SPWM. An analytical formulation of phase-voltage THD for UVS-based SPWM MLIs is derived and utilized for the novel SPWM-based OMTHD. Validation is carried out by theoretical analysis, digital simulations, and real-time controller + Hardware-in-Loop (C-HIL)-based experiments.

Trade-off between transient response and grid-side current quality is a well-known issue of single-phase mains-connected power converters. A dual-loop control structure (usually based on PI or type-II controllers) is typically employed in such systems to regulate the DC link voltage to a constant reference (in order to maintain power balance) while forcing the grid-side current to have a specific shape (in order to comply with power quality requirements). Introducing notch term/s (tuned to certain multiple/s of the mains base frequency) into one of the loops allows either for the improvement of the dynamic performance without worsening the total harmonic distortion of grid-side current or for the enhancement of the current quality without impairing the dynamic response. Since the maximum tolerable value of total harmonic distortion is typically imposed by a certain power quality standard, it is desirable to enhance the transient response of the power converter system as much as possible while keeping the total harmonic distortion at the maximum allowed value. However, universal off-grid operating power conversion systems must support both 50 Hz and 60 Hz mains; consequently, tuning the notch term/s to 50 Hz multiple/s would not be sufficient for a 60 Hz mains operation and vice-versa. Consequently, this work examines the possibility of introducing a dual-notch term into the control loop in order to cover both above-mentioned base frequencies. It is demonstrated that under typical base frequency uncertainty values, the performances of dual-notch terms are nearly decoupled so that the term tuned to a 50 Hz frequency (and optionally to its multiples) has nearly no influence at a 60 Hz mains operation and vice-versa. Consequently, the methodology allows for the improvement of the dynamics of universal grid-connected power converters without total harmonic distortion (THD) deterioration. A stability analysis of the proposed control structure is carried out and quantitative design guidelines, allowing for the attainment of an optimized dynamic response for a given maximum tolerable total harmonic distortion, minimum allowed phase margin and a certain base frequency uncertainty, are established. It is shown that a DC link voltage loop bandwidth of 52 Hz may be attained while keeping the grid-side current THD below 5%. Simulations and experimental results support well the proposed design methodology.

This article examines the impact of a power factor on the behavior of partial DC link voltages in three-phase three-level AC/DC (or DC/AC) converters operating without additional balancing hardware. We consider the case in which the controller utilizes a bandwidth-restricted (DC in steady state) zero-sequence component to achieve average partial DC link voltage equalization since the injection of high-order zero-sequence components is impossible or forbidden. An assessment of partial split DC-link capacitor voltage behavior (particularly that of ripple magnitudes and phases) is necessary for, e.g., minimizing the values of DC link capacitances and selecting reference voltage values. Previous studies assessed the abovementioned behavior analytically for operation under a unity power factor based on third-harmonic-dominated split partial voltages’ ripple nature. However, it is shown here that deviation from the unity power factor introduces additional (to the third harmonic) non-negligible harmonic content, increasing partial voltage ripple magnitudes and shifting their phase (relative to the mains voltages). As a result, the third-harmonic-only assumption is no longer valid, and it is then nearly impossible to derive corresponding analytical expressions. Consequently, a numerical approach is used in this work to derive a generalized expression of normalized ripple energy as a function of the power factor, which can then easily be utilized for assessments of split DC link voltage behaviors for certain DC link capacitances and reference voltages. Simulations and experimental results validate the proposed methodology applied to a 10 kVA T-type converter prototype.

Output current of inductive wireless power transfer links (IWPTLs) with battery loads is influenced by coupling coefficient and input–output voltage. To regulate the output current while keeping the operational frequency near resonance, dc–dc converters are often added at IWPTL input and/or output, increasing system complexity and dimensions while reducing lifetime and reliability. On the other hand, a sub-resonant frequency control method was shown to eliminate the need for dc–dc converters addition as well as preventing IWPTL overrating. The technique is based on imposing bifurcation (or frequency splitting) and varying the operational frequency within certain region below resonance to regulate IWPTL output current. Due to the fact that some applications restrict the operational frequency band, methodology for deriving the design space of sub-resonant frequency-controlled series–series (SS)-compensated IWPTL (SS-IWPTL) operating under frequency constraints with constant current (CC) output is proposed in this work. The algorithm identifies all feasible combinations of loosely coupled transformer (LCT) coils self-inductances and coupling coefficients for expected ranges of input–output voltages and prescribed operational frequency band, allowing to maintain CC output. Simulations and experiments are carried out to verify the proposed methodology.

The well-known trade-off between dc link voltage dynamics and ac-side current quality in power factor correction (PFC) rectifiers limits attainable dc link voltage loop bandwidth. It has been shown that adding a notch filter in series with the typically employed PI or type-II regulator allows improving dc link voltage dynamics without sacrificing total harmonic distortion (THD). However, clear quantitative guidelines for PI + Notch (PI + N) controller design to attain prescribed values of ac-side current THD and dc link voltage undershoot (response to a step-like load power increase) were not established so far. Consequently, analytical expressions linking the coefficients of the PI + N controller with the above-mentioned performance merits for a given value of dc link capacitance are revealed in this article. Corresponding dc link voltage loop gain phase margin and crossover frequency expressions are derived and the feasibility region of the proposed design guidelines is clearly indicated. Simulations and experimental results validate the proposed design methodology.

The article presents the analytical derivation of the minimum dc link capacitance in single-phase front ends with active power factor correction (PFC) without hold-up time requirements. Such systems typically employ boost-type rectifiers; operate under restricted total harmonic distortion (THD) of the grid-side current. Moreover, PFC rectifiers must be capable of tolerating step-like zero-to-rated load power variations. It is well known that these two constraints contradict each other, posing nontrivial design challenges. The revealed value of minimum capacitance is expressed by an explicit function of grid voltage and frequency, converter rated power, dc link voltage reference, and grid current THD and voltage loop phase margin set points. Experimental results validate the proposed methodology, closely matching corresponding analytical predictions.

Output current of inductive wireless power transfer links (IWPTLs) with battery loads is influenced by coupling coefficient and input–output voltage. To regulate the output current while keeping the operational frequency near resonance, dc–dc converters are often added at IWPTL input and/or output, increasing system complexity and dimensions while reducing lifetime and reliability. On the other hand, a sub-resonant frequency control method was shown to eliminate the need for dc–dc converters addition as well as preventing IWPTL overrating. The technique is based on imposing bifurcation (or frequency splitting) and varying the operational frequency within certain region below resonance to regulate IWPTL output current. Due to the fact that some applications restrict the operational frequency band, methodology for deriving the design space of sub-resonant frequency-controlled series–series (SS)-compensated IWPTL (SS-IWPTL) operating under frequency constraints with constant current (CC) output is proposed in this work. The algorithm identifies all feasible combinations of loosely coupled transformer (LCT) coils self-inductances and coupling coefficients for expected ranges of input–output voltages and prescribed operational frequency band, allowing to maintain CC output. Simulations and experiments are carried out to verify the proposed methodology.

Electronic Capacitor (EC) is formed by a bidirectional DC-DC converter terminated with small auxiliary capacitance. The device is capable of mimicking the behavior of a bulk DC link capacitor while actually employing a component with much lower capacitance value. The paper demonstrates that forcing an EC to emulate a negative capacitance while connecting it in series with a passive capacitor leads to DC-DC converter rating reduction and subsequent potential volume reduction and efficiency increase of a DC link. Such a device may replace a traditional bulk DC link capacitor present in power electronics supported distributed energy resources in a plug-and-play manner. Simulations and experiments of a common dual stage AC/DC power conversion system employing the proposed active DC link validate the methodology.

This paper introduces a new architecture for a high-resolution digital pulse-width modulator (HR-DPWM) which generates multiple output phases, all synchronized and derived out of a single reference source. Constructed through digital standard-cell delay chain and simple combinatorial logic, the module produces PWM signals with configurable on-time, period and time-delay (between phases) with resolution of a single delay-element. To minimize the statistical error spread (e.g. jitter error) between phases, a single delay-line is utilized to generate a master time-base while combinatorial logic assigns per-phase independent duty ratio settings. The resultant module minimizes the time-diversity error between phases, as any uncertainty in the on-time generation is identical between phases. The solution is compact, flexible and scales with the number of phases. Since the entire architecture is realized through standard cells, the solution also scales with fabrication technology and is described by HDL, which translates onto hardware using automated process. The HR-DPWM module has been designed and fabricated on a 0.18µm 5V CMOS process, totaling 0.08mm2 of effective silicon area. Experimental results of a four phase 13-bit HR-DPWM are provided, demonstrating high accuracy and linearity characteristics with time resolution of 200ps and excellent matching and tracking between all phases.

The most important performance merits of inductive wireless power transfer links (IWPTL) operating at load-independent-voltage-output (LIVO) frequency are efficiency and output characteristics. It was recently demonstrated that none-series (NS) compensated IWPTL operating at LIVO frequency outperforms its series-series (SS) and series-none (SN) compensated counterparts in terms of efficiency. In order to complete the comparison, this paper presents output characteristics modeling and analysis (namely, relation between output voltage and load power) of a practical NS-compensated IWPTL operated at LIVO frequency. It is demonstrated that even though the system is operated at LIVO regime, its output voltage remains load-dependent due to practical issues. The lower bound of the output voltage range corresponds to operation under rated loading and is derived using phasor domain equivalent circuit, assuming continuous conduction mode (CCM) of the receiving-side diode rectifier without neglecting equivalent series resistances. On the other hand, upper bound of the output voltage range corresponds to operation under zero loading (inevitably imposing discontinuous conduction mode (DCM) of the receiving-side diode rectifier) and is obtained using time-domain solution of corresponding differential equations system due to the fact that classical phasor analysis fails to accurately describe DCM operating NS-compensated IWPTL. The proposed method is applied to a 1 kW, 400 V NS-compensated IWPTL operated at LIVO frequency and is well-verified by simulations and experiments. Comparison with output voltage characteristics of SS and SN-compensated IWPTLs assert the advantage of NS-compensated topology.

In this article, a simple closed-form analytical expression for the line-voltage total harmonic distortion (LTHD) of three-phase staircase-modulated (SCM) multilevel inverters (MLI) is proposed. The revealed expression is valid for any conventional MLI topology with arbitrary number and parity of voltage levels. The proposed formulation is presented as an analytic function of the number of voltage levels (N) and the phase switching angles (PSA); thus, it is suited to MLIs of equal voltage source supply and of any topology. This function may be employed for accurate LTHD calculation and optimization. The results are verified against LTHD calculations and optimizations, obtained numerically from previous works. Both processor in loop (PIL)- and controller + hardware in loop (C-HIL)-based real-time experimental validations are included as well. A downloadable file containing the Maple and MATLAB functions of the proposed expression are also provided.

Staircase Modulation (SCM) is a popular switching strategy for multilevel inverters (MLI), which is often a preferable alternative to Pulse Width Modulation (PWM) due to its reduced switching losses, especially for MLIs with a relatively high number of voltage levels (N). In some applications, such as motor drives, or when output filters are applicable, SCM may also suit MLIs with moderate N values. While MLIs with Equal DC Sources (EDCS) are more common, MLIs with Unequal DC Sources (UDCS), such as asymmetric Cascaded H-Bridge (CHB) MLIs are known to further reduce the waveforms’ Total Harmonic Distortion (THD). The main objective of SCM is to adjust the waveform’s fundamental component, while employing some harmonic mitigation strategy, such as THD minimization. Such an optimization approach relies on an accurate THD formulation, which eliminates underestimation errors associated with numerical THD approximations. This paper reveals novel generic analytical formulations of both Phase-voltage THD (PTHD) for single-phase MLIs and Line-voltage THD (LTHD) for three-phase MLIs. The revealed exact formulation approach is derived from Fourier series representation of THD, resulting in simple closed-form PTHD and LTHD expressions, applicable to any MLI topology, with either EDCS or UDCS configurations, and arbitrary value of N (odd and even). Given an arbitrary N value, the proposed formulations can be used to generate symbolic N-level PTHD or LTHD expressions, which are symbolic functions of the Phase Switching Angles (PSA) and (optionally) the DC source Ratios (DCR). The revealed THD formulations are verified and compared against recently introduced time-domain-based THD formulations. It is shown that when both time and frequency-based formulations are employed in THD minimizations to form a novel Hybrid Temporal-Spectral (HTS) Optimal Minimization of THD (OMTHD) approach, even better results can be achieved. The novel OMTHD is deeply explored and verified by both digital simulations and Controller + Hardware in Loop (C-HIL) based real-time experiments using 7- and 8-level three-phase MLI configurations. A downloadable supplemental file containing Maple and MATLAB functions of the proposed THD expressions, as well as pre-calculated sets of optimum variables for different values of N is provided for readers’ convenience.

Series-none compensated induction wireless power delivery link (SN-IPDL) was recently shown to be capable of achieving minimal complexity receiver with reduced losses in case of strong coupling, typical for applications such as power delivery into enclosed compartments such as industrial glove boxes and close-range inductive heating. Common practical applications often feature power delivery to varying loads which require a stable operational voltage. Operation at LIVO frequency allows establishing potentially feedback-free wireless power delivery with constant output voltage for varying loads. The paper reveals that due to nonzero equivalent series resistances and invalidity of the first-harmonic-approximation (FHA) based equivalent circuit, the output voltage remains affected by the load despite operation at LIVO frequency, residing within a certain range of values, lower and upper bounds of which correspond to rated and zero loading, respectively. This must be considered during SN-IPDL system design in order to assure that output voltage stays within allowed bounds for relevant loading conditions. This paper derives analytical expressions for output voltage bounds of a power-loaded series-to SN-IPDL, functioning at load-independent-voltage-output (LIVO) frequency. Time domain differential equations (DE)-based analysis is applied to derive the two bounds and allows (as a by-product) establishing an alternative FHA-based equivalent circuit of SN-IPDL operating in continuous conduction mode. Simulations and experiments based on 380V, 1.2 kW-rated prototype demonstrate excellent matching with analytical outcomes, validating the proposed analysis.

Trade-off between DC link voltage dynamics and AC-side current quality in grid-interfacing power converters limits the attainable DC link voltage loop bandwidth for a given desired value of grid-side current total harmonic distortion (THD). It was recently shown that adding a notch filter in series with the typically employed DC link voltage controller of PI or type-II structure releases the above trade-off, yet requires full controller re-design. The paper proposes to replace the notch filter by a plug-in disturbance observer, allowing to increase attainable DC link voltage loop bandwidth for given grid-side current THD without any modification of the existing DC link voltage controller by utilizing a special frequency-selective filter. Simulations and experimental results validate the proposed design methodology.

The study sets a baseline for split DC link capacitance values and voltage set points in three-phase three-level AC/DC (or DC/AC) converters operating with unity power factor. In order to equalize the average values of partial DC link voltages, the controller generates a zero-sequence containing DC components only while employing neither dedicated DC link capacitance balancing hardware nor high-order zero-sequence component injection. Such a baseline is required in order to evaluate the effectiveness of different DC link capacitance reduction methods proposed in the literature. Unlike most previous works, utilizing neutral point current based on cumbersome analytical expressions to determine neutral point potential oscillations, the instantaneous power balance-based approach is employed in this paper, resulting in greatly simplified and more intuitive expressions. It is demonstrated that while the total DC link voltage is low-frequency ripple-free under unity power factor balanced AC-side operation, split DC link capacitors absorb triple-fundamental frequency power components with one-sixth load power magnitude. This yields significant opposite phase partial voltage ripples. In such a case, selection of DC link capacitances and voltage set points must take into account the expected values of AC-side phase voltage magnitude and split DC link capacitor voltage and current ratings. Simulation and experimental results validate the proposed methodology by application to a 10 kVA T-type converter prototype.

This article focuses on improving the control structure of electronic capacitor (EC), formed by a bidirectional dc-dc converter terminated with small auxiliary capacitance. Typical application of such a system is mimicking the dynamic behavior of a bulk dc-ink capacitor while actually employing a component with much lower capacitance value. It was previously revealed that EC may be treated as output-voltage regulated wide-input-range converter feeding a bidirectional power load. Dual-loop voltage-current linear cascaded regulator, typically employed for EC terminal voltage control, imposes slow unstable mode when absorbing power from the dc-link. This article demonstrates that performing a transformation from voltage-current to power-energy domain by feedback linearization-based nonlinear control simultaneously eliminates the unstable mode and increases control bandwidth. Revealed findings are well-supported by simulations and experiments.

Unlike grid-connected and motor driving converters, typically exchanging sinusoidal current with the grid/motor, inverters employed in uninterruptible power supplies and active power filters generate periodic, harmonics-rich currents. Consequently, current controller in these applications must be capable of accurate tracking of references containing high harmonic count, calling for a multiresonant structure. On the other hand, major disturbances influencing the current loop comprise output and dc link voltages, which can typically be measured/estimated and cancelled by a feed-forward action. Thus, the current regulation problem is reduced to tracking challenge only. Recently, methodology for designing single-parameter single-resonant controllers according to desired tracking behavior of ac signal amplitude was proposed by the authors. However, as shown in the article, straightforward extension of the algorithm to multiresonant case is unfeasible. Nevertheless, it is possible to obtain an accurate approximation utilizing the decoupling property of resonant terms in both frequency and time domains. As a result, simple single-parameter multiresonant controller design guidelines are derived, imposing similar transient response to each individual harmonic of periodic reference. Simulations and experimental results validate the proposed design methodology.

Staircase Modulation (SCM) is a popular switching strategy for three-phase multilevel inverters (MLI) of higher voltage levels count (N). SCM is often combined with some harmonic mitigation strategy, such as a minimum of Total Harmonic Distortion (THD) in addition to output fundamental component adjustments. While voltage THD-based SCM is desirable in many applications, it is not a panacea for all applications, especially for motor drives and grid-connected MLIs, where minimization of current-THD is preferable. A THD alternative performance parameter, called frequency-Weighted Total Harmonic Distortion (WTHD) can serve as a strong indication of current-THD, especially in inductive loads. For three-phase MLIs with 3-wire loads, line voltage waveform has more significance than phase voltage waveform, as it directly impacts the load’s current quality. For this reason, the minimization of Line-voltage WTHD (WLTHD) may be preferred over the minimization of THD, Line-THD (LTHD) or WTHD. Since WLTHD involves complicated expressions, it is typically calculated and expressed using frequency-domain numerical approaches, often resulting in underestimation errors. In this paper, a novel analytical WLTHD formulation for three-phase SCM-based MLIs is revealed and used for subsequent WLTHD minimization with the aim of minimizing load current-THD for 3-wire inductive loads. The proposed WLTHD formulation is a function of all possible Phase Switching Angles (PSA), valid for any MLI topology with arbitrary values of N, either odd or even. Moreover, it is shown that the existing WLTHD minimization approach is a particular case of the proposed generic methodology. The derived formulation, which can produce mathematically exact symbolic WLTHD results, is verified against numerically obtained results in previous works. Controller + Hardware in Loop (C-HIL) based validation is also carried out for 7-level three-phase MLIs feeding an induction motor for current-THD optimization, revealing significant improvements compared to previously obtained methods. The proposed WLTHD minimization possess the highest correlation to current-THD, even for nearly resistive loads. Links for downloading MATLAB and Maple source files of proposed WLTHD formulations as well as pre-calculated optimum PSA results for 5 ≤ N ≤ 16, covering most of the practical cases, are also provided for reader’s convenience.

Low-temperature gradients between massive solids and ambient air are ubiquitous due to a diurnal temperature cycle. The use of these gradients as a source of renewable energy to power the low power-consuming nodes of a wireless sensor network instead of batteries can solve the problem of periodic replacement of batteries with their subsequent recycling. This study successively presents the stages of modeling, development, optimization, assembling, and experimental validation of a thermoelectric harvester for replacement of a 20 Ah battery for a wireless water quality sensor located on a water pipe. The experiments confirmed that the thermoelectric harvester produces more than 0.5–2 mW at a temperature difference of about 1–2 K between the pipe surface and the surrounding air at the calm wind speed of about 1 m/s. The original dimensionless model of thermoelectric harvester is presented herein. The key role of convective heat transfer in the harvesting process is demonstrated.

The brief proposes a modification of classical pure resistive first harmonic approximation (FHA) based equivalent of diode rectifier in series-series compensated inductive wireless power transfer link (SS-IWPTL), operating at load-independent-voltage-output (LIVO) frequency. It is shown by means of time-domain analysis that a load-independent inductance should be added in parallel with the typically utilized load-dependent resistance to accurately represent input rectifier impedance at operating frequency. It is also shown that the worst case (minimal) inductance value is obtained when equivalent series resistances (ESRs) are ignored. In practical systems, non-zero ESRs are typically present and are typically desired to be as low as possible to increase the power transfer efficiency. It is shown that increasing the ESRs leads to escalation of equivalent resistance and inductance values (i.e. reducing the influence of the latter), without altering the load-independence characteristics of equivalent inductance. Simulations and experiments based on a 400 V, 1 kW strongly-coupled SS-IWPTL operating at LIVO frequency validate the proposed analysis.

Some popular applications of wireless power transfer (such as electric vehicle charging) include a transmitter residing on a static platform (charging station) and a dynamic receiver (vehicle). In such applications, compensation may be excluded from the receiver in order to minimize, simplify and lower the cost. If transmitter compensation is also maximally simplified series to none (SN) compensation topology is created. It was recently shown that classical first harmonic approximation (FHA) based analysis fails to accurately predict RMS values of system currents, thus overestimating the achievable coil-to-coil efficiency. Consequently, this paper establishes modified FHA (MFHA) equivalent circuit of SN-compensated inductive power transfer link (IPTL), utilizing analytical expressions of primary and secondary currents based on time-domain differential equations (DE) based solution. It is shown that the outcomes of proposed MFHA and DE methods are very close, justifying the proposed methodology. Simulations and experiments demonstrate excellent matching, validating the presented analysis.

The paper presents practical considerations and guidelines for designing an improved-efficiency contactless inductive power transfer link, delivering DC power in step-down mode to an electromagnetic levitation melting system residing in a sealed compartment. The proposed arrangement employs none-series compensated inductive power transfer link operating at the so-called “load-independent-voltage-output” frequency, allowing feedback-less and sensor-less design. However, the output voltage of a system operating at such frequency remains influenced by the load to some extent, residing within a certain range with boundary values (minimum and maximum) corresponding to maximum (rated) and minimum load, respectively. Consequently, the proposed contactless power delivery system is first analyzed using both first harmonic approximation (frequency-domain) based approach and differential equations (time-domain) based method to obtain corresponding output voltage bounds. Then, coil-to-coil efficiency and optimal load matching factor are determined. Comparison with both typically utilized symmetrical series-series and recently proposed series-none compensation topologies reveals the superiority of none-series compensation topology in terms of coil-to-coil efficiency for the whole range of coupling coefficients. Simulations and experiments of 400 V, 1 kW none-to-series compensated inductive wireless power transfer link, delivering contactless energy to a 250 V electromagnetic levitation melting system, demonstrate excellent matching and accurately validate the presented analysis.

This paper proposes an algorithm for the extraction of primary-side first harmonic voltage and current components for inductive wireless power transfer (WPT) links by employing quadrature demodulation. Such information allows for the accurate estimation of corresponding receiver-side components and hence permits the monitoring of the output voltage and resistance necessary for protection and/or control without using either sensors or feedback communication. It is shown that precision estimation is held as long as the parameter values of the system are known and the phasor-domain equivalent circuit is valid (i.e., in continuous conduction mode). On the other hand, upon light load operation (i.e., in discontinuous conduction mode), the proposed technique may still be employed if suitable nonlinear correction is employed. The methodology is applied to a 400 V, 1 kW inductive WPT link operating at a load-independent-voltage-output frequency and is well-verified both by simulations and experiments.

The paper puts forward a method for predicting output voltage and resistance of a series-series (SS) compensated inductive wireless power transfer (IWPT) link operating at load-independent-voltage-output (LIVO) frequency. The link is a part of the static system (reported by the authors in earlier works), wirelessly delivering power into an enclosed compartment without any secondary-to-primary feedback. The proposed algorithm employs input DC-side quantities (which are slow-varying and nearly noise-free, thus measured utilizing low-cost, low-bandwidth sensors) only to monitor output DC-side quantities, required for protection and/or control. It is shown that high estimation accuracy is retained as long as system parameter values are known and the phasor-domain equivalent circuit is valid (i.e., upon continuous-conduction mode (CCM) of the diode rectifier, where the proposed methodology utilizes the recently revealed modified diode rectifier equivalent model for enhanced accuracy). Under light loading (i.e., in discontinuous conduction mode (DCM)), a nonlinear correction is combined with the proposed technique to retain accuracy. The proposed methodology is well-verified by application to a 400 V to 400 V, 1 kW static IWPT link by simulations and experiments.

The letter reveals that for a given operating frequency, infinite amount of compensation capacitor pairs exists, yielding load independent voltage gain of a typical series-series compensated resonant inductive wireless power transfer link (WPTL). Closed-form analytical expression is derived, linking the values of compensating capacitors with the desired load independent voltage gain based on given coil inductances, coupling coefficient and operating frequency. Feasible range of achievable voltage gains is shown to be bounded by the value of coupling coefficient based on a novel 4-parameter generalized loosely coupled transformer model. Experimental results are given to validate the presented findings.

The paper presents analytical investigation and hands-on design of inductive wireless power transfer link for a through-glass AC power delivery system into enclosed compartment such as industrial glove box or vehicle cabin. The system is fed from AC grid and creates a standard AC outlet within the enclosed compartment, capable of supplying loads of up to 1 kW. The system consists of three (namely, AC/DC, DC/DC and DC/AC) conversion stages, with the former and the latter realized by standard off-the-shelf units. The intermediate DC-DC power conversion stage, which is the paper focus, is realized by a from-scratch-built inductive wireless power transfer link, operating in load-independent voltage output regime without any feedback. It was recently shown that the output voltage of such a system, even when operating at load-independent frequency, remains influenced by the load due to practical issues. As a result, the output voltage resides within a certain range rather than remains constant, obtaining minimum/maximum values under rated load/no-load conditions, respectively. Since coils separating glass width typically possesses some finite uncertainty, values of both coupling coefficient and coils self-inductances may be different than nominal (design) ones and hence the output voltage would drift from its nominal range. Hence, due to the fact that upper and lower bounds of an inductive wireless power transfer link output voltage range are limited by DC link capacitor and DC/AC power stage constraints, tolerated glass width uncertainty is obtained in the paper. Moreover, compensating capacitors pair symmetrizing uncertainty tolerance of the inductive wireless power transfer link is also revealed. Simulations and experiments based on 400 V, 1 kW-rated inductive wireless power transfer link are presented to validate the analysis.

The letter reveals two additional basic compensation topologies for resonant inductive wireless power transfer links (supplementary to the existing four) created by placing both compensation capacitors either on primary or secondary side, leaving the opposite coil uncompensated. This produces parallel-series/none and none/series-parallel topologies, with the latter being more practical due to its suitability to operation with typically utilized voltage-source inverters.

It is well-known that continuous conduction mode (CCM) operation at certain frequency yields nearly load-independent voltage gain in practical series-series compensated inductive wireless power transfer links (SS-IWPTL). Such an operation is usually referred to as “load independent voltage output” (LIVO). Residual load dependence is due to the presence of non-zero equivalent series resistances in both transmitter and receiver. On the other hand, it has been shown that voltage gain remains load-dependent at the same operating frequency in discontinuous conduction mode (DCM) irrespectively of equivalent series resistances values. Consequently, the output voltage of SS-IWPTL operated at LIVO frequency resides within a range with lower bound corresponding to rated load and upper bound corresponding to zero loading for a given input voltage. The upper bound expression (typically attained in CCM) is derived using the first harmonic approximation (FHA) based equivalent circuit and is well-established by previous works. On the contrary, derivation of the lower bound (achieved in DCM) requires differential equation (DE) based analysis and was barely treated in the literature. The paper demonstrates that lumped capacitance of receiving side coil and input capacitance of receiving side rectifier must be taken into account during DE-based analysis since they impose significant receiving side voltage oscillations, which may give rise to safety issues. In order to damp these oscillations and keep the output DC voltage below a predetermined limit, minimal loading should be applied at the SS-IWPTL output, creating an RCD-snubber equivalent. Guidelines for the minimal load sizing are derived in the paper analytically. Simulations and experiments based on a 400V, 1kW SS-IWPTL operating at LIVO frequency demonstrate excellent matching, validating the proposed analysis.

It is well-known that levitation melting type induction heating system, fed by resonant inverter, is a complex and nonlinear dynamical system, in which high-frequency electrical-side dynamics and low-frequency mechanical side dynamics are strongly coupled. Such systems are typically operated at resonant electrical frequency in order to both stabilize the open-loop dynamics and maximize the power transfer. While stable, resulting open-loop dynamics is typically nonlinear and highly underdamped, depending on both floating object vertical position and operation frequency. Oscillative behavior of high-temperature work piece being melted is obviously undesired due to safety issues. In order to address the issue, this paper first derives small-signal operation point dependent linearized dynamics of the system, based on the recently established envelope modeling methodology. Then, model reduction is carried out within bandwidth of interest. It is shown that both linearized control-to-output and disturbance-to-output transfer functions may accurately be represented by second-order dynamics with operating point dependent gains, natural frequencies and damping factors within the bandwidth of interest. Once derived, reduced system representations are employed in active damping feedback controller design, in which operation frequency rather than one of mechanical-side variables is utilized as feedback signal, making the proposed algorithm sensorless. It is shown that suggested methodology influences only the damping factor of original system while leaving both gain and natural frequency unaltered and is capable of eliminating oscillative response throughout the whole operation range. Simulations and experimental results are shown to validate both reduced-order linearized dynamics and the proposed active damping methodology.

When feeding a constant-resistance or constant-voltage type load, inductive wireless power transfer link (IWPTL) operating as current source is typically desired. Moreover, in case coupling coefficient between transmitter and receiver is constant, load-independent current output (LICO) characteristics are beneficial, allowing the system to operate without feedback. Moreover, near zero phase angle (ZPA) operation is also valuable, allowing to minimize volt-ampere rating of the transmitting-side inverter. A new LC/S compensated IWPTL topology, capable of simultaneously achieving LICO and ZPA, was recently revealed in the literature. The proposed compensation network consists of one inductor and two capacitors. This paper generalizes the LC/S compensated IWPTL topology by first deriving the compensating elements set based on a novel loosely-coupled transformer (LCT) equivalent circuit and then enlightening that for certain values of primary compensation inductor, secondary compensation capacitor should either be omitted or replaced by an inductor in order to preserve LICO and ZPA. Thus, an LC/S compensated IWPTL may actually operate in three different regions, each calling for specific sub-type of LC/S compensation. Design guidelines for compensation parameters selection are provided in this paper, allowing to achieve virtually any value of load-independent current output for a given LCT coils pair. Moreover, expressions for calculating normalized component stresses are obtained for all three regions of operation, taking into account nonlinear nature of transmitting-side inverter and receiving-side rectifier, as opposed to typical phasor-domain based approach, which ignores higher-order harmonics. Analytical results based on obtained expressions are well-supported by their real-time-domain counterparts.

The paper presents a methodology for nonlinear envelope dynamics derivation of a levitation melting type induction heating system, fed by a resonant inverter, based on recently established work piece electro-mechanical model. The work piece under consideration is formed by an aluminum sphere, floated by conical-shaped copper coil. Resonant power converter is used to drive the induction heating system due to the fact that significant impedance of the work piece coil at high operation frequency (several tens of kilohertz) limits the power transferred to the load and therefore needs to be cancelled by corresponding capacitive impedance. Since the application requires levitation of the object being heated up, low-frequency (several hertz) dynamics appears, related to floating body movement. As a result, high-frequency electrical signals become modulated by low-frequency oscillations induced by mechanical side dynamics. It is known that power transfer in sinusoidal excited electrical system is governed by magnitudes and related phases of currents and voltages. Consequently, in order to assess both the low-frequency dynamics of levitated object mechanical motion and the amount of power transferred, information regarding envelope behavior of electrical-side signals is sufficient. Once established, envelope model of the electrical subsystem combined with typical model of the mechanical subsystem describe mechanical side parameters (position, speed and acceleration) exactly as if full electrical model would have been utilized. Moreover, envelope model significantly decreases simulation time and memory requirements of simulation platform. The proposed modeling approach is validated by comparing full and envelope model simulation results, accompanied by results obtained from experimental prototype.

In this letter, explicit analytic expression of output voltage total harmonic distortion (THD) in staircase modulated single-phase multilevel inverters (MLI) is derived and verified. The revealed nonrecursive formulae is expressed as a simple function of all possible switching angles, valid for generalized MLI irrespectively of the topology and number of voltage levels (odd or even). The proposed expression may be utilized for accurate calculation of THD values, eliminating the risk of underestimation associated with typical frequency-based (numerical) approaches adopted by modern computational software packages.

The article proposes an in-depth analysis of a series-series compensated resonant inductive wireless power transfer (WPT) link, operating at load-independent frequency while feeding a power load. It is shown that due to the presence of equivalent series resistances in practical systems, a load-independent operation point is only an approximation. The output voltage is still affected by the load, obtaining minimum and maximum values under rated load and no-load operation, respectively. While the output voltage value under rated load is typically well predicted by the commonly used first-harmonic-approximation-based equivalent circuit, the latter is unsuitable for obtaining the output voltage value under light loading due to nonlinearity caused by the discontinuous conduction mode of the secondary. Time-domain analysis is, therefore, used to accurately predict the WPT output voltage value under zero-load operation and accurately derive the expected WPT output voltage range in the load-independent regime. Simulations and experiments based on a 400-V 1-kW WPT link demonstrate excellent matching, validating the proposed analysis.

In this paper, decoupled electro-mechanical modeling of a resonant-inverter-fed electromagnetic levitation melting system (in which a conductive body is floated by Lorentz force and heated-up by high frequency magnetic field-created eddy currents) is carried out and validated experimentally. The work piece considered is formed by a metallic sphere placed in a conical-shaped coil. The proposed model consists of an electrical side subsystem formed by series resonant circuit with time-varying resistance and inductance, a typical second-order mechanical subsystem and a highly nonlinear link between the two. It is also shown that the power conversion process is similar to that of a loosely-coupled transformer, on which any wireless power transfer system is based. Therefore, the system should be powered by a resonant high-frequency AC source to both stabilize vertical axis dynamics and maximize the transferred power. Moreover, operation under resonant conditions yields an explicit relation between operation frequency and vertical position of levitating sphere, leading to possibility of position-sensorless implementation. 1 kW-rated experimental prototype, based on 210Vdc-fed inverter, operating at switching frequency of around 25 kHz is built and tested to validate the derived model. The inverter forces 300A current flowing through 8-turns conical coil in which a 2.27 g sphere is levitated. Simulation and experimental results are shown to accurately resemble each other, verifying well the proposed modeling approach.

This paper presents a modification of the Vienna rectifier (VR) to obtain more than three voltage levels at the DC line connection, while preserving the unity power factor at the AC grid side. The proposed unidirectional multilevel there-phase rectifier, called the “Negev rectifier”, has a reduced device count and utilizes a unique novel Time Division Multiplexed based control scheme, which makes the challenging N-level VR expansion possible. The Negev rectifier can serve as a grid interface for supplying dc voltage to multilevel inverters with 4 up to 7 voltage levels, eliminating the burden of inverter-side voltage balancing control. The Negev hardware can be constructed by two complementary topologies, making it suitable for either high current or high voltage applications.

Weighted total harmonic distortion (WTHD) is an important performance merit, representing either current or voltage quality of voltage source inverters. Unlike general (non-weighted) THD, which can be evaluated using a closed-form analytic time-domain expression, WTHD is typically calculated using approximate frequency-domain numerical approaches. The paper reveals a novel analytic WTHD expression for output voltage of Staircase Modulated (SCM) single-phase Multi-Level Inverters (MLI). The proposed formula, valid for SCM MLI of arbitrary topology with any number and parity of voltage levels, is a function of all switching angles (SA) only and may thus be easily implemented in common symbolic/numeric computing software. Due to its analytical nature, the WTHD expression yields highly accurate results, eliminating the risk of round-off and underestimation errors, associated with conventional frequency-based numerical approaches. Furthermore, based on the proposed formula, Optimal Minimization of WTHD was carried out for accurate calculation of optimum SA, yielding minimum WTHD for desired modulation index. Eight sets of high-resolution (1171 samples per level) look-up tables, linking desired modulation index to optimum SA values, were generated. A downloadable file, containing MATLAB coded WTHD functions and the eight look-up tables, are provided as a shortened URL. In order to verify the proposed expression, analytic WTHD values are compared with results obtained in previous works. In addition, the methodology was validated utilizing Processor-in-Loop simulation of 7 and 8 level SCM MLI.

The brief presents some principles of the ON/OFF operational strategy applied to energy management of a hybrid internal combustion engine (ICE) based auxiliary power unit (APU). It is shown that significant reduction of fuel consumption (78% for the example system presented) and maintenance expenses (80% operation time decrease was attained by the system) may be achieved by such a strategy, shifting the system operation point towards corresponding optimal region. The side effect of aggravated amount of starting events is cured by employing an actively balanced supercapacitor (SC)-based emergency starter (SCS). The SCS operates as short-time energy storage device, charging from the battery at a low rate and then providing a current burst required for proper internal combustion engine starting. Current sensorless method of automatic connection (based on bus voltage sensing) and disconnection (based on sensing the voltage across bidirectional MOSFET-based switch) of the SCS is also proposed. The proposed circuitry, successfully validated by experiments, may be arbitrarily scaled up or down according to application rating.

Interest in autonomous low-power energy sources has risen with the development and widespread use of devices with very low energy consumption. Interest in thermoelectric harvesters has increased against this background. Thermoelectric harvesters, especially harvesters on-chip, have peculiar properties related to the thermal route, thermal transients, and spatial temperature distribution within the chip. A behavioral model of the harvester is required for engineers to successfully develop voltage converters with maximum power point tracking and energy storage units. There are accurate models based on the finite element method, but these models are usually not compatible with simulators of electrical circuits, and therefore are not convenient for designers. Existing equivalent circuit models fit this requirement, but usually do not consider many parameters. This article proposes an original method that allows simulating spatial thermoelectric processes by analogy with the finite difference method, using electrical circuits simulations software. The study proposes a complete methodology for building the model and examples of simulations of one-, two- and three-dimensional problems, as well as examples of simulation of macro problems in the presence of external thermal and electrical devices, such as heatsink and electrical load.

The specific power storage capabilities of double-layer ultracapacitors are receiving significant attention from engineers and scientific researchers. Nevertheless, their dynamic behavior should be studied to improve the performance and for efficient applications in electrical devices. This article presents an infinite resistor–capacitor (r–C) chain-based mathematical model for the analysis of double layer ultracapacitors. The internal resistance and capacitance were measured for repetitive charging and discharging cycles. The magnitudes of internal resistance and capacitance showed approximately ±10% changes for charge-discharge processes. Electrochemical impedance spectroscopy investigations revealed that the impedance of a double-layer ultracapacitor does not change significantly in the temperature range of (−30 °C to +30 °C) and voltage range of (0.3376–2.736 V). The analysis of impedance data using the proposed mathematical model showed good agreement between the experimental and theoretical data. The dynamic behavior of the ultracapacitor was successfully represented by utilizing the proposed infinite r–C chains equivalent circuit, and the reverse Fourier transform analysis. The r–C electrical equivalent circuit was also analyzed using the PSIM simulation software to study the dynamic behavior of ultracapacitor parameters. The simulation study yields an excellent agreement between the experimental and calculated voltage characteristics for repetitive charging-discharging processes.

The study suggests a method aimed to improve the performance of practical grid-connected converters connected todistorted mains, utilising total uncertainty and disturbance estimator (TUDE) based control structures with time-delay filter. Sucha TUDE filter enhances disturbance rejection performance by possessing near-unity magnitude and near-zero phase at integermultiples of the base frequency, imposing repetitive-control-alike behaviour. However, it is well-known that in repetitive control,disturbance rejection at mid-frequencies, were non-periodic disturbances and noise may exist, is deteriorated. This studypresents an enhancement, allowing to retain good disturbance rejection at mid-frequencies within the low-frequency portion ofcontrol bandwidth (relevant in practical systems) while trading-off the performance in the high-frequency control bandwidth part.The proposed methodology is verified by application to output current control of LCL-filter based inverter feeding distorted ACmains. The validity and performance of the proposed methodology are well-supported by simulations and experiments.

The paper presents a methodology of assessing performance of thermoelectric harvesters (TEH) operating at low temperature gradients using manufacturer datasheet only. Simplified and full TEH models with temperature-independent parameters are established with the former developed in the form of a two-terminal equivalent circuit, typical for renewable energy generators. Normalized expression is derived to assess maximum extractable TEH power for certain environmental conditions, heat sink thermal resistance and thermoelectric module figure of merit. Key role of the heat sink in TEH performance is revealed and corresponding design guidelines are provided. Experimental results are provided, demonstrating close match with analytical predictions, obtained by the proposed methodology.

Staircase Modulation (SCM) is a commonly employed switching strategy in Multilevel Inverters (MLI) with a high number of voltage levels (N). The main challenges in SCM are adjusting the Modulation Index (MI) to the desired value while minimizing the Total Harmonic Distortion (THD). This is achieved by solving an objective function for its optimum variables. These variables are the Switching Angles (SA) in the case of an MLI with Equal DC voltage Supply (EDCS), or both the SAs and the DC voltage supply Ratios (DCR), in the case of an MLI with Unequal DC voltage Supply (UDCS). Such an approach, which is referred to as Optimum Minimization of THD (OMTHD), relies on the accuracy of the THD expression used for the objective function. This paper reveals generic analytical closed-form formulations of both Phase-voltage THD (PTHD) for single-phase (1φ) MLIs and Line-voltage THD (LTHD) for three-phase (3φ) MLIs. The revealed THD expressions apply to SCM based MLIs of any topology, with either EDCS or UDCS voltage source configurations, which may be fixed or varying, and arbitrary value of N (odd and even). Given an arbitrary N value, the proposed unified formulations can be used to generate symbolic N-level PTHD or LTHD expressions, which are analytical functions of the SA and (optionally) DCR variables. The proposed THD expressions were used to form a generic OMTHD problem and solve for optimum SA and DCR variables, ensuring PTHD or LTHD minimization, subject to a set of optional constraints, such as the target MI, tolerable Modulation Error (ME), and the Maximum DCR (MDCR). Outcomes of the proposed OMTHD algorithm were successfully verified by Controller + Hardware-in-Loop (C-HIL) based experiments and compared against results of previous works, raveling significant improvement in THD accuracy and MLI’s performance. A downloadable supplemental file containing Maple and MATLAB functions of the proposed THD expressions, as well as pre-calculated sets of optimum SAs and DCRs tables for 13 different values of N (4 ≤ N ≤ 16), is provided for readers’ convenience.

This study establishes a set of frequency-domain phase margin-oriented quantitative design guidelines for deriving coefficients of optimised multi-resonant AC current regulators, consisting of series-connected terms. Such an arrangement allows straightforward extension of existing design guidelines for developing coefficients of optimised single-resonant AC current regulators. Practical restrictions imposed by, relatively, low switching frequency are also considered, yielding corresponding design guidelines generalisation.

This paper introduces a new zero current switching topology for parallel balancing of serially connected batteries string. The main advantage of the balancing concept in this study is that energy is transferred only when the cells are unbalanced. As a result, the power losses are significantly reduced since no current circulates through the system when balanced. This has been enabled by a modification of an isolated series-resonant converter operating in a discontinuous conduction mode. A single transformer for two cells is used, as opposed to conventional isolated topologies that require a transformer per cell. The realization is simple and sensorless. Experimental results have been obtained by a prototype of two modules balancing four series-connected batteries.

In the article “Analysis, design, and optimization of LC/S compensation topology with excellent load-independent voltage output for inductive power transfer,” by Yao et al., a novel LC/S (primary series-inductor parallel-capacitor/secondary series-capacitor) compensation topology was proposed. A single set of three-compensating-elements was derived, allowing to simultaneously attain LIVO and zero-voltage switching (ZVS). However, the inverter was not able to operate at a zero-phase angle (ZPA), minimizing its volt-ampere rating, with the proposed compensating element set. Since the proposed topology is extremely promising, the purpose of this note is to complement the presented analysis by pointing out the following: 1) A group of infinite three-compensating-elements sets exists (to which the set derived in the article belongs to), allowing to simultaneously achieve LIVO and ZVS; and 2) A unique three-compensating-elements set exists, allowing to simultaneously achieve LIVO and ZPA.

It is well-known that in ac-grid-connected or motor-driving converters, current behavior directly sets the exchange of power between the two. Moreover, in corresponding current plants, most of the disturbance (formed by grid voltage or back EMF and the dc-link voltage) may be measured/estimated and appropriately canceled, reducing the current regulation problem to tracking challenge only. The latter is still of extreme importance since the amount of active/reactive power exchanged is proportional to current magnitude and phase. Recently, a method for deriving proportional-resonant controller structure and coefficients according to desired tracking behavior of ac signal amplitude, applied to typical power converter current loop, was proposed based on the fact that if ac signal envelope is perceived as dc signal, its transient behavior may be easily shaped utilizing well-known approaches employed in dc systems loop shaping while keeping zero phase tracking error at all time. This paper extends the proposed methodology by introducing in-depth analysis of the resulting loop gain shaping, applying practical issues, such as actuator delay, damping, and finite word length to the system, yielding a closed set of hands-on design guidelines. Experimental results are also given, providing a two-fold value: successfully validating the presented material and demonstrating that some of the previously reported outcomes (based on simulations) cannot be achieved in practice due to the above mentioned real world constraints.

In this paper, a two-degrees-of-freedom control algorithm based on uncertainty and disturbance estimator (UDE), aimed to minimize the total harmonic distortion of inverter output voltage is proposed, possessing enhanced robustness to fundamental frequency variations. A multiple-time-delay action is combined with a commonly utilized low-pass UDE filter to increase the range of output impedance magnitude minimization around odd multiples of fundamental frequency for enhanced rejection of typical single-phase nonlinear loads harmonics. Marginal robustness improvement achieved by increasing the number of time delays is quantified analytically and revealed to be independent of delay order. The performance of the proposed control approach and its superiority over two recently proposed methods is validated successfully by experimental results.

In this brief, extension of known rules for designing optimized single-resonant ac current regulators to multiresonant current regulators parameter selection for single-phase grid-connected photovoltaic inverters is proposed. The proposed generalization is made possible by utilizing multiplied rather than summed resonant terms within the controller. A set of phase-margin oriented design guidelines is established, explicitly defining each controller parameter to corresponding figure of merit. Simulations and matching experimental results are shown to verify the proposed approach.

Active capacitance reduction circuits (ACRCs) are dc-dc converters, terminated by a small auxiliary capacitor, typically utilized to replace bulk electrolytic capacitors in dual-stage grid-connected power conversion systems. Electronic capacitors are ACRCs supporting “plug-and-play” operation in addition to the ability to emulate virtually any finite capacitance at dc-link connected terminals. Despite excellent steady-state functionality, all ACRCs possess the poor response to steplike no-load-to-fullload (and vice versa) transients due to the fact that the auxiliary capacitor utilized (and thus corresponding energy stored) is much smaller than the bulk dc-link capacitor being replaced. Nevertheless, in grid-feeding applications where fuel cells of photovoltaic generators act as a power source, the rate of generated power change is limited. This is also true regarding some off-grid systems such as LED lighting with dimming, where sudden load changes are unnecessary and electronic capacitors seem to be directly applicable in such systems. Therefore, this paper reveals the limits of steplike and ramplike load variations, tolerable by a system equipped with an electronic capacitor, based on its power rating and auxiliary capacitance value utilized. Examples are given for typical systems with 400-V dc link, connected to 50-Hz mains. The validity of presented findings is well-supported by simulations and experiments.

A novel method for controlling direct voltage regulated active dc-link capacitance reduction circuits (ACRC) is proposed in this paper. Instead of forcing the dc-link voltage of the power conversion system to follow a constant reference, the ACRC imposes dc-bus voltage in proportion to the integral of its input current. Consequently, it resembles an adjustable value capacitor from the dc-link side. Therefore, as opposed to existing control strategies, the proposed method simultaneously allows the dc-link voltage to reflect the power balance of the system and the pulsating power component to be diverted into significantly reduced auxiliary capacitance via a bidirectional dc-dc converter. As a result, replacing bulk dc-link capacitance by the proposed circuitry does not require any modification of existing grid-connected power conversion system controllers, thus allowing plug-and-play operation. The proposed approach is validated by application to a commercial power factor correction front end by both simulations and experiments.

This paper reveals the design and implementation of a magnetic actuation system (MAS) with noninvasive displacement measurement by current sensing only. A platform-independent MAS modeling methodology is utilized, describing the cross-coupled system behavior by the physical representation of mechanical and electromagnetic counterparts. An extended nonlinear inductor model is developed, demonstrating the challenging control task of displacement regulation. The inductor model facilitates the development of a combined current sensing methodology employing noninvasive displacement measurement. The combined sensor, based on adding a “shunt inductor” in series to the main actuator, performs both high-resolution displacement and dc current measurement with fast response and minimum losses. The MAS model and the combined sensor-based operation have been experimentally verified on a single-axis levitator prototype.

The paper suggests a method aimed to improve the performance of dynamical systems with periodic uncertainties and disturbances (ac power converters are typical representatives of such systems) utilizing frequency-domain disturbance observer (DOB)-based control structure. In such control arrangement, DOB filter is the key component and should be designed so that its magnitude (phase) is as close to unity (zero) as possible at frequencies where the total uncertainty and disturbance exists. The methodology for designing DOB filters is well established mostly for systems with slow-varying uncertainties/disturbances and has been barely extended to systems with periodic excitation (such as grid-connected or stand-alone ac power converters). In this study, systematic enhancement of DOB filters, designed according to the classical methodology, is suggested based on appropriate mixing with a series multiresonant term. The proposed approach allows attaining improved periodic signals rejection capability while significantly sacrificing neither the dc gain nor the crossover frequency. Quantitative design guidelines are provided, and possible tradeoffs are revealed. The proposed methodology is validated by application to current control of LCL-filter-based inverter connected to a distorted ac grid. Feasibility and performance of the suggested approach are well supported by simulations and experiments.

This paper proposes a modified uncertainty and disturbance estimator (UDE) structure, aimed to improve the ability to approximate and eliminate signals characterized by periodic behavior. The algorithm combines delay action with low-pass filtering, introducing high loop gain magnitude values at multiple frequencies of interest while retaining implementation feasibility by imposing finite crossover frequency, similarly to repetitive control. For a given control bandwidth, the modified UDE is shown to outperform the classical one in terms of disturbance rejection at the expense of slight phase margin loss. Simulations and experiments are given to support the feasibility of the proposed control structure, applying the revealed modification to the current control of an LCL inverter, connected to a distorted ac grid.

This Letter proposes a simple realisation of a circuit (referred to aselectronic capacitor) capable of emulating large capacitance of control-lable value while utilising a much smaller capacitor and a DC–DC con-verter. The circuit may be used in a plug-and-play fashion instead ofany real large capacitor within the control bandwidth. The proposedcontrol algorithm forces the terminal voltage of the DC–DC converterto follow the well-known capacitance equation by sensing the terminalcurrent and simultaneously compensates conversion losses by anauxiliary control loop. The proposed algorithm is successfully verifiedby emulating bulk DC-link capacitance of a commercial power factorcorrection front end.

In this paper, a two-degrees-of-freedom control algorithm based on uncertainty and disturbance estimator (UDE), aimed to minimize the total harmonic distortion of inverter output voltage is proposed, possessing enhanced robustness to fundamental frequency variations. A multiple-time-delay action is combined with a commonly utilized low-pass UDE filter to increase the range of output impedance magnitude minimization around odd multiples of fundamental frequency for enhanced rejection of typical single-phase nonlinear loads harmonics. Marginal robustness improvement achieved by increasing the number of time delays is quantified analytically and revealed to be independent of delay order. The performance of the proposed control approach and its superiority over two recently proposed methods is validated successfully by experimental results.

Owing to the good trade-off between implementation and performance, fixed-step direct maximum power point tracking techniques (e.g., perturb and observe and incremental conductance algorithms) have gained popularity over the years. In order to optimize their performance, perturbation frequency and perturbation step size are usually determined a priori. While the first mentioned design parameter is typically dictated by the worst-case settling time of the combined energy conversion system, the latter must be high enough to both differentiate the system response from that caused by irradiation variation and match the finite resolution of the analog-to-digital converter in case of digital implementation. Well-established design guidelines, however, aim to optimize steady-state algorithm performance while leaving transients nearly untreated. To improve transient behavior while keeping the steady-state operation unaltered, variable step direct maximum power point tracking algorithms based on adaptive perturbation step size were proposed. This paper proposes a concept of utilizing adaptive perturbation frequency rather than variable step size, based on recently revised guidelines for designing fixed-step direct maximum power point tracking techniques. Preliminary results demonstrate the superiority of the proposed method over adaptive perturbation step size operation during transients, without compromising the steady state performance.

The paper presents a full theoretical analysis of thyristors-bridge-type superconducting fault current limiter (SFCL) operational modes, supported by MATLAB/SIMULINK-based simulations. Both normal and fault current operation conditions of a SFCL-based power system under continuous conduction mode (CCM) and discontinuous conduction mode (DCM) are treated. The developed equations are shown to be valid for all possible thyristor-firing angles. Derived analytical relations are useful for both comprehensive design of thyristors-bridge-type SFCLs and analysis of circuit simulator based outcomes.

This Letter generalises frequency-domain oriented design guidelinesfor optimised single-resonant three-parameter AC current regulatorsfor grid-connected converters. Unlike in previously established set ofdesign guidelines, possible practical restrictions imposed by relativelylow-switching frequency are taken into account in the proposedmethodology. In addition, resonant term bandwidth is selected accord-ing to the desired robustness to fundamental frequency variations. As aresult, a closed set of three non-linear equations is created. The solutionmaximises the loop gain crossover frequency for a given phase marginwhile respecting frequency robustness and resonant gain restrictions,set a priori.

The heuristic perturb-and-observe-based maximum-power-point tracking (MPPT) algorithm of photovoltaic (PV) generator is still the most popular technique in use, despite the broad spectrum of developed other MPPT algorithms. The correct direction of the next perturbation step requires that the previous perturbation is settled down properly and the applied perturbation step size is large enough to overcome the PV-power changes induced by the varying irradiation level and/or the power-grid-originated PV-voltage ripple. The requirements for the minimum perturbation step size are well defined in the available literature. The design equations to predict the PV-power settling time are derived by assuming that the PV-interfacing converter operates in continuous conduction mode (CCM). A large perturbation step size may drive the interfacing converter to enter into discontinuous conduction mode (DCM), which will delay the PV-power settling process and destroy the validity of the predicted settling times. In order to avoid confusing the MPPT process, the maximum perturbation step size has to be limited as well. This paper provides theoretical foundations for the proper design of the maximum step size based on the DC-DC interfacing-converter dynamic behavior. The theoretical findings are validated with experiments as well as by simulations by means of a boost-type DC-DC converter and real PV panel.

A loop compensator design for power electronic converters is typically phase margin oriented due to widely varying operation point and actuator delay. The former challenge has been successfully treated recently by uncertainty and disturbance estimator (UDE) based controllers owing to their two-degrees-of-freedom nature, allowing nearly independent tuning of tracking and disturbance rejection performance. On the other hand, actuator-imposed constraints have not been discussed in UDE-related literature by far. It is well known that in order to fully utilize the available control bandwidth, actuator dynamics must be taken into consideration. Consequently, this paper reveals guidelines for UDE-based controllers design considering typical actuator dynamics under phase margin constraint, set a priori. The proposed method is then applied to power control of a multimode bidirectional noninverting buck-boost converter, connecting two dc microgrids. Simulations and experimental results are given to support the revealed findings.

In this paper, an unconventional method of dc link bulk capacitance active reduction without ripple increase in mains-connected power conversion systems is proposed. Even though the adopted power circuitry (a bidirectional dc–dc converter, terminated by a much smaller capacitance) is analogous to solutions proposed up to date, the concept of operation is quite different. Rather than controlling the current, flowing into the dc link (i.e., operating as a current controlled current sink, similarly to an active power filter), suggested solution regulates the ripple by controlling the dc link voltage (i.e., operating as a voltage controlled current sink) thus letting the grid-interfacing converter OFF the task. This allows widening of the dc link voltage loop bandwidth and, as a result, reducing the ripple for the same capacitance utilized or reducing the capacitance while maintaining the same ripple without trading off the power factor. In order to validate the proposed methodology experimentally, it is successfully applied to a single-phase off-the-shelf power factor correction pre-converter.

Due to relatively good performance and simple implementation, fixed-step direct maximum power point tracking (MPPT) techniques such as perturb and observe and incremental conductance are the most popular algorithms aimed to maximize the energy yield of photovoltaic energy conversion systems. In order to optimize the MPPT process performance, two design parameters-perturbation frequency and perturbation step size-need to be set a priori , taking into account the properties of both interfacing power converter and photovoltaic generator. While perturbation frequency is limited by the combined energy conversion system settling time, perturbation step size must be high enough to differentiate system response from that caused by irradiation variation. Recent studies have provided explicit design guidelines for single-loop MPPT structures only, where the algorithm directly sets the interfacing converter duty cycle. It was shown that dynamic resistance of the photovoltaic generator, which is both operation point and environmental conditions dependent, significantly affects the combined energy conversion system settling time. On the other hand, no design guidelines were explicitly given for multiloop MPPT structures, where the algorithm sets the reference signal for photovoltaic generator (PVG) voltage and inner-voltage controller performs the regulation task. This paper introduces perturbation frequency and perturbation step size design guidelines for such systems. It is shown that while perturbation step size design is similar to that of single-loop structures, perturbation frequency design is quite different. It is revealed that once the inner-voltage loop is properly closed, the influence of PVG dynamic resistance on settling time (and thus on perturbation frequency design) is negligible. Experimental results are provided to verify the proposed guidelines validity.

In this paper, tracking versus disturbance rejection tradeoff is revealed and quantitatively investigated for systems utilizing uncertainty and disturbance estimator (UDE)-based controllers. The tradeoff appears to be due to finite control bandwidth, characterizing any real-world application. Based on the exposed findings, guidelines for designing UDE controllers are provided, and respective operational limits are indicated. It is shown that two operation points exist on performance envelope, characterized by similar disturbance rejection, while yielding different tracking performance. Moreover, it is demonstrated that typical proportional-integrative controllers, designed using zero-pole cancellation, are a particular case of UDE controllers. As an example, the proposed method is applied to average current control of a bidirectional noninverting multimode buck-boost converter. Simulations and experimental results are provided to validate the research outcomes.

The paper focuses on control analysis and operational issues of a recently proposed direct voltage regulated active capacitance reduction circuit, consisting of a small auxiliary capacitance interfaced to dc link by bidirectional dc-dc converter. The aim of such a system is replacing the bulk dc bus capacitor without escalating the ripple. While the hardware of the system under study is similar to some of the proposed active capacitance reduction solutions, the control structure is quite different. The primary goal of the controller is direct regulation of dc-link voltage rather than dc-link current, performed by most of existing solutions, thus avoiding the use of invasive dc-link current measurement/s. It is revealed that such an active capacitance reduction circuitry may be perceived as output-voltage regulated wide-input-range converter feeding a bidirectional power load. Such an arrangement was neither mentioned nor analyzed in the literature by far, requiring nontrivial and challenging control design. A dual-loop voltage-current arrangement widely used in typical power supplies is proposed to control the active capacitance reduction circuitry. It is shown that the control structure is sufficient to yield satisfactory performance even though the system possesses a slow unstable mode when absorbing power from the dc link. The revealed findings are fully supported by simulations and experimental results.

In this paper, a novel method of maximum power point tracking of renewable energy generators is proposed, utilizing the sum of dynamic and static conductance as maximum power point tracking loop variable. This allows to formulate the maximum power point tracking problem as a typical closed-loop stabilization task of non-linear static plant with zero reference. Consequently, a simple integrative controller is shown to be sufficient to ensure zero steady-state maximum power point tracking error with easily determinable nominal dynamics. A recently revealed method of online photovoltaic generator dynamic conductance estimation allowing robust terminal voltage control is utilized. Moreover, it is revealed that the resulting maximum power point tracking loop plant is piecewise linear around the maximum power point, i.e. for given environmental conditions two different convergence rates are expected, depending on the relative value of operating voltage to maximum power point voltage. Presented analytical outcomes are verified by application of the proposed maximum power point tracking structure to a grid-connected photovoltaic generator system under robust voltage control.

In this paper, a method to directly shape the output impedance of an inverter is proposed to reduce the total harmonic distortion of the output voltage, based on the uncertainty and disturbance estimator (UDE)-based robust control framework. It is shown that, because of the two-degree-of-freedom feature of the UDE-based control strategy, the UDE filter directly affects the inverter output impedance. A multi-band-stop filter instead of a commonly adopted low-pass filter is then proposed to directly minimize the output impedance around the harmonics to reduce the effect of nonlinear loads and assure robustness to frequency variations. Two tradeoffs are revealed: one between filter bandwidth and stability and the other between robustness and the number of harmonics suppressed. The effectiveness of the proposed control strategy is fully supported by experimental results.

In order to enhance maximum power point tracking (MPPT) speed of photovoltaic generators (PVGs) upon fast irradiation changes, maximum power line (MPL)-based control is often used. MPL is a curve, linking all possible MPP coordinates for a given temperature. In the literature so far, PVG MPL was either assumed linear, which is inaccurate for all irradiation levels, or possessed photocurrent dependence, requiring real-time estimation of the latter. In this letter, an irradiation-independent explicit expression for PVG MPL is derived, valid for all practical irradiation levels, thus allowing real-time implementation without the need of photocurrent estimation.

In order to optimize the performance of direct (or perturbative) fixed-step maximum power point tracking algorithms (e.g., perturb and observe and incremental conductance), two design parameters-perturbation frequency and step size-must be selected. The main requirement for perturbation frequency design is ensuring the period between two successive perturbations is longer than settling time of photovoltaic generator power transient. According to existing design guidelines, perturbation frequency should be selected at maximum power point, corresponding to standard test conditions. However, due to finite resolution of digital controllers, maximum power region rather than single maximum power point exists in practice. Therefore, operating point can arbitrarily reside within this region, belonging either to constant-current or constant-voltage I-V curve parts. It is shown that the photovoltaic generator power transient settling process is significantly slower in constant current than maximum power region due to increased value of dynamic resistance. Consequently, perturbation frequency design should be carried out in constant-current region rather than at maximum power point. Short-circuit condition should be selected as worst-case design operation point, where photovoltaic generator dynamic resistance obtains highest value. Then, perturbation frequency design becomes photovoltaic generator independent, influenced only by interfacing converter component values. Experimental results validate presented findings successfully.

In this paper, a method for suppressing the low-frequency portion of dc-link ripple inevitably present in power conversion systems with reduced capacitance is proposed. The discussed active capacitance reduction circuitry (consisting of a feedback-controlled shunt-connected bidirectional buck-boost converter, terminated by a small auxiliary capacitance) directly regulates the dc-link voltage, utilizing a dual-loop control structure with parallel-connected multiresonant-bank-enhanced voltage loop stabilizing controller to achieve nearly constant, low-frequency-ripple-free steady-state dc-link voltage. Consequently, the proposed active capacitance reduction system may be perceived as a virtual infinite capacitor from the dc link point of view. The suggested circuitry is successfully applied to a single-phase commercial power factor correction front end in a nearly plug-and-play fashion. The control algorithm effectiveness is fully supported by simulations and experimental results.

Linear robust controller design based on Uncertainty and Disturbance Estimator theory for nonlinear uncertain single-input single-output systems with external disturbances is discussed in the paper with application to the output voltage control of a unidirectional universal multimode buck/boost/buck–boost converter. The converter is characterized by different nonlinear static and dynamic behaviour in each of the operating modes. The proposed controller forces the system to maintain nearly nominal performance through the whole range of operation space by appropriately estimating and cancelling the terms including nonlinearities, parametric uncertainties and external disturbances. In addition, measurement noise is included in the analysis to demonstrate the trade-offs of the proposed method. Despite the non-triviality and relative complexity of the method, the resulting controller structure is simple, allowing low-cost, low-part-count analogue implementation. Extended simulation results are presented to demonstrate the effectiveness of the proposed control approach.

In order to enhance the maximum power point tracking (MPPT) speed of solar generators, offline calculated maximum power line (MPL) is often used as a feed-forward signal added to the output of MPPT controller. MPL is nonlinear static electrical characteristic of renewable energy generators connecting all the maximum power points for given temperature. In this letter, electrical side MPL is derived for a typical wind turbine generator (WTG). It is shown that MPLs of solar and wind generators possess similar structure, supporting the similarity between the two energy conversion processes.

Functional equivalence of three nonmodel-based variable-step-size maximum power point tracking (MPPT) algorithms is revealed in this paper by establishing general closed-loop controller-plant structure of corresponding MPPT control loops, allowing us to formulate the problem as a typical stabilization task. The MPPT loop plants may be separated into three main components, two of which are similar and the third one, namely stabilization function estimator, is the main reason for the performance differences of the discussed methods in case the MPPT loop controllers are alike. It is shown that in case the estimator convergence rate is much faster than the MPPT loop bandwidth, similar low-frequency performance may be expected by utilizing any of the three methods.

In this paper, a robust nonlinear control strategy is developed for a class of second-order nonlinear uncertain systems with uncertainties and disturbances and is applied to two-axis active magnetic bearing position stabilization. The approach is based on a feedback linearization method, robustified by the uncertainty and disturbance estimator, which calculates and robustly cancels system uncertainties and disturbances via appropriate filtering. The controller uses the information regarding the known part of plant dynamics while the terms containing unknown dynamics are treated as additional system uncertainties and disturbances. The algorithm provides excellent performance in stabilizing the active magnetic bearing position and rejecting disturbances both at standstill and under movement. Simulations are given to show the effectiveness of the strategy via an application to an experimentally derived active magnetic bearing model.

In the paper “Design of alpha-filter based UDE controllers considering finite control bandwidth” by A. Kuperman (Nonlinear Dynamics, vol. 81, no. 1, July. 2015), performances of a new first-order alpha-filter for uncertainty and disturbance estimator (UDE)-based control and a classical first-order UDE filter where examined. It was shown that performance superiority of the alpha-filter is not straightforward and takes place for limited operating region only in case practical implementation issues of the filters are taken into account. The purpose of this note is complementing Kuperman in Nonlinear Dyn 81:411–416 by proving that in case practical implementation restrictions are extended to the overall control system and classical UDE-filter-based controller would always outperform the alpha-filter-based controller in terms of disturbance and noise rejection, while the alpha-filter-based controller would be superior in terms of stability.

Stationary reference frame proportional-resonant (PR) controllers have recently became a viable alternative to rotation reference frame proportional-integrative compensators in ac applications because of their ability of achieving zero steady-state error without the need for computational-intensive reference frame transformations. While extensive efforts have been put into performance comparison of the two control schemes, design of PR controllers according to desired closed-loop time-domain transient performance was barely investigated. This letter proposes a method for deriving PR controller structure and coefficients according to desired transient behavior of ac signal amplitude, applied to typical power converter current loop. The method is based on the fact that if ac signal envelope is perceived as dc signal, its transient behavior may be easily shaped utilizing well-known approaches employed in dc systems loop shaping while keeping zero phase tracking error at all times. On the other hand, while desired transient performance is easily achieved, the relation between crossover frequency and transient processes time constant is not as straightforward as in dc systems. The validity of the presented theoretical analysis is evaluated by simulations.

In this paper, a robust control method based on a disturbance observer is proposed to regulate the terminal voltage of a photovoltaic generator, interfaced by a current mode-controlled boost dc-dc converter. The combined generator-converter-load system possesses a nonlinear behavior, highly dependent on operation point and environmental variables, thus burdening the control task. It is shown that employing a typical linear controller, designed according to a single nominal operating point, results in a closed-loop performance, varying from a highly overdamped near open-circuit condition to greatly underdamped around short-circuit conditions. On the other hand, when the proposed robust controller is utilized, the closed-loop performance remains nearly nominal throughout the whole operation range. In addition, it is shown that, by sacrificing the performance in the vicinity of the open-circuit point, it is possible to implement the controller using a single op-amp with a reduced part count. Simulation and experimental results are presented to verify the proposed method.

Nonlinear characteristics of photovoltaic generators were recently shown to significantly influence the dynamics of interfacing power stages. Moreover, since the dynamic resistance of photovoltaic generators is both operating point and environmental variables dependent, the combined dynamics exhibits these dependencies as well, burdening control challenge. Typically, linear time invariant input voltage loop controllers (e.g. Proportional-Integrative-Derivative) are utilized in photovoltaic applications, designed according to nominal operating conditions. Nevertheless, since actual dynamics is seldom nominal, closed loop performance of such systems varies as well. In this paper, adaptive control method is proposed, allowing to estimate photovoltaic generator resistance online and utilize it to modify the controller parameters such that closed loop performance remains nominal throughout the whole operation range. Unlike previously proposed method, utilizing double-grid-frequency component for estimation purposes and suffering from various drawbacks such as operation point dependence and applicability to single-phase grid connected systems only, the proposed method is based on harmonic current injection and is independent on operating point and system topology.

Recently, a new first-order alpha-filter for uncertainty and disturbance estimator-based control was proposed to achieve reduced tracking and estimation errors in the presence of fast-varying uncertainties and shown to be capable of keeping the steady-state error within acceptable limits by appropriately choosing filter parameters. The purpose of this note is to demonstrate operation limits of the new filter and quantify performance enhancement by taking practical implementation issues and restrictions into account.

In this paper, robust UDE-based linear control strategy is developed for a class of second-order nonlinear uncertain systems with disturbances. After revealing the control structure and performing stability analysis, the robust control strategy is used to suppress wing rock motion. The approach is based on the uncertainty and disturbance estimator, which calculates and robustly cancels system uncertainties and input disturbances via appropriate filtering. The information regarding the known part of the linear plant dynamics is used by the controller; the terms containing the nonlinear functions are treated as additional uncertainties to the system. The algorithm provides excellent performance in suppressing the wing rock dynamics and rejecting disturbances. Simulations are given to show the effectiveness of the strategy via an application to an experimentally derived delta wing rock model.

In this paper, design process and functionality of a portable single-panel dual-battery solar charger prototype are presented, achieving energy density of 571 Wh/kg during a typical 3-day infantry mission. The device may instantaneously charge up to two Li-ion MR-2791 batteries, supporting plug-and-play operation. The system consists of a lightweight custom solar panel, based on 20% efficient monocrystalline photovoltaics, and an intelligent power processing module. The panel contains eight transparent polymer-encapsulated and camouflaged series-connected six solar cell packs with antiparallel diodes, allowing partial shading operation. The power processing module consists of two synchronous current-mode-controlled buck converters, digital signal processor, and a microcontroller, supporting both maximum power point tracking of the solar panel with partial shading detection and multimode charging of Li-ion packs while instantaneously communicating with the batteries. Power management algorithmic design is presented, based on ensuring system stability while supporting the required operation modes. System implementation stages and underlying issues are thoroughly discussed, and utilized hardware components are presented in detail. Experimental results of system testing under real outdoor conditions are presented to demonstrate the device functionality and energy yield capabilities. Copyright © 2015 John Wiley & Sons, Ltd.

Stationary frame (AC) currents behaviour of three-phase converters with synchronous frame (DC) controllers shaping is explicitly linked. It is revealed that closed-loop synchronous frame dynamics determines amplitude behaviour of stationary frame signals without affecting their frequency and phase. Consequently, synchronous frame current controllers design should actually be based on desired stationary frame amplitude transient performance.

A nonlinear robust control strategy is proposed in this paper to deal with wing rock motion. The method is based on the disturbance observer enforced contraction theory results. The disturbance observer calculates and robustly cancels system uncertainties and input disturbances. The information regarding the known part of the nonlinear plant dynamics is used by the controller, while the uncertainties and disturbances are treated as an additional input to the system and dealt with by the disturbance observer. The algorithm demonstrates good performance in damping the oscillations while rejecting the disturbances. Simulations are provided to demonstrate the effectiveness of the proposed method via an application to an experimentally derived delta wing rock model operating in both nominal and uncertain environments.

In this article, one linear and one nonlinear robust control strategies are proposed for uncertain nonlinear continuous-time systems with disturbances and state delays. The approaches are based on the uncertainty and disturbance estimator (UDE) introduced in 2004. In the case of a linear controller, the terms containing the nonlinear functions and time delays are treated as additional disturbances to the system. In the case of a nonlinear controller, both known and unknown delay scenarios are considered. In the case of an unknown time delay, the terms containing the delay are treated as additional disturbances to the system. The algorithms provide excellent tracking and disturbance rejection performance. Simulations are given to show the effectiveness of the strategies, first via a simple example and second via an application to a continuous stirred tank reactor system.

In this paper, a robust control strategy based on the uncertainty and disturbance estimator (UDE) is extended and applied to uncertain linear continuous-time systems with state delays and disturbances. It does not require the knowledge of the bounds of uncertainties and disturbances. Both known and unknown delay cases are considered. In the case of an unknown time delay, the term with the delay is treated as an additional disturbance to the system. The proposed algorithm shows excellent tracking and disturbance rejection capabilities. The robust stability of LTI-SISO systems is analysed and simulations are given to show the effectiveness of the UDE-based control.

The manuscript extends the method of testing the motion controllers’ robustness by emulating uncertainties and disturbances, caused by real loads and mechanical and electrical parameter variations to multiloop motor drives. Such a contribution is important since multiloop drives are widely used in the industrial environment. The proposed technique requires neither connecting physical load nor actually changing any parameter of the electric drive under test. The microprocessor of the motor drive itself creates the effect of the load torque and parameter variations by applying equivalent feed-forward commands to the corresponding loop controller using digital signal processing software. As a result, the electric drive is virtually perturbed, and the controllers’ behavior resembles the performance of a really perturbed drive controllers. The present method, which can be related to a class of Hardware-in-the-Loop Simulations, can be used to test the implementation of robust control algorithms or at didactic purposes using motion control kits found on the market. Simulations and experimental results validate the proposed algorithm, applied to a Brushless DC motor drive, demonstrating an excellent agreement.

The control algorithm based on the uncertainty and disturbance estimator (UDE) is a robust control strategy and has received wide attention in recent years. In this paper, the two-degree-of-freedom nature of UDE-based controllers is revealed. The set-point tracking response is determined by the reference model, whereas the disturbance response and robustness are determined by the error feedback gain and the filter introduced to estimate the uncertainty and disturbances. It is also revealed that the error dynamics of the system is determined by two filters, of which one is determined by the error feedback gain and the other is determined by the filter introduced to estimate the uncertainty and disturbances. The design of these two filters are decoupled in the frequency domain. Moreover, after introducing the UDE-based control, the Laplace transform can be applied to some time-varying systems for analysis and design because all the time-varying parts are lumped into a signal. It has been shown that, in addition to the known advantages over the time-delay control, the UDE-based control also brings better performance than the time-delay control under the same conditions. Design examples and simulation results are given to demonstrate the findings.

Purpose– The purpose of this paper is to present a method to compensate slow varying disturbances and plant parameter drifts using a simple yet robust algorithm called input-output nominalization. Design/methodology/approach– In case of known uncertainties, an analytical expression of pre-computed feed-forward compensation command is derived. In presence of unknown disturbances and parameter drifts, the control algorithm uses a proportional-integrative estimator-based nominalizer. It creates a nominalizing signal, reflecting the deviation of the system from its nominal form using plant input and output. The signal is subtracted from the nominal controller output to cancel the uncertainty and disturbances effects. Findings– As a result, the uncertain plant and the nominalizer quickly converge to the nominal plant. Therefore, a simple controller tuned according to the nominal plant can be used despite the disturbances and parameter drifts and a nominal response is always obtained. Simulation and experimental results are given to describe the control algorithm performance and inherent limitations. Researchlimitations/implications– The proposed method is suitable for linear systems with low frequency uncertainties and disturbances only. Practical implications– The technique allows compensating errors in plant parameter identifications as well as parameter drifts during plant operations. Constant and slow varying disturbances are also rejected, allowing obtaining a prescribed nominal response. Originality/value– The proposed approach is different from the common robust control methods to the uncertain linear systems control. Instead of designing a robust controller, efforts are concentrated on the plant input-output nominalization in a fashion similar to input-output linearization. The method allows compensating slow varying disturbances and plant parameter drifts using a simple algorithm leading to a simple controller tuned according to the nominal plant parameters.

A method that allows emulation of parameter uncertainties and external disturbances without any mechanical and electrical parts supplementary to the electric drive is proposed. The emulating signal reflecting the desired changes is created in software and added to the nominal controller output, forcing the unperturbed motor output to resemble the output of a motor with actual uncertainties and disturbances. The proposed method allows simultaneous emulation of any combination of parameter variations and unpredicted disturbances. The method can be related to a class of advanced hardware-in-the-loop simulations, where the nominal hardware is present in the test bed in addition to the controller. The technique can be used to thoroughly test the performance of advanced control algorithms before mass production or for didactic purposes in an educational laboratory using motion control kits found on the market. Simulation and experimental results are reported to prove the feasibility of the proposed approach.

Design of a battery-ultracapacitor semiactive hybrid for powering pulsed current loads is presented in this paper. The semiactive hybrid energy source consists of an ultracapacitor assisted Li-Ion battery, connected to the load via a dc-dc converter. The system is controlled such that the battery is supplying a near-constant current to satisfy the average load demand while the ultracapacitor supplies the dynamic component of the load current. The control algorithm is based on a well-known capacitance-emulating approach. As a result, a high-energy battery can be used despite the high-power load demand spikes. In addition, the battery-load voltage matching is not required and the control algorithm does not require load current sensing. It is shown that the proposed system performance is equivalent to the performance of a passive hybrid, employing a very high nonfeasible capacitance. Moreover, it is revealed that the battery current is independent of the capacitor size, which affects the load voltage ripple only. Extended simulation and experimental results are presented to demonstrate the feasibility of the approach.

A simple low cost algorithm for induction motor mechanical parameters estimation without speed sensor is presented in this paper. Estimation is carried out by recording stator terminal voltage during natural braking and subsequent offline curve fitting. The algorithm allows accurately reconstructing mechanical time constant as well as loading torque speed dependency. Although the mathematical basis of the presented method is developed for wound rotor motors, it is shown to be suitable for squirrel cage motors as well. The algorithm is first tested by reconstruction of simulation model parameters and then by processing measurement results of several motors. Simulation and experimental results support the validity of the proposed algorithm.

In this paper, simple approach to analyzing the starting procedure of synchronous motors (SMs) is presented with an emphasis on the pull-in process. Instead of the classical, mostly intuitive pulling-repelling torque approach, an analytical method based on the motor mechanical part swing equation is employed. Factors affecting starting and pull-in processes are clearly indicated and torque impulse balance leading to a pull into step is revealed. It is shown that if the motor fails to pull into step within a single oscillation, it can still be synchronized during one of the succeeding acceleration periods. The crucial role of the excitation winding energizing instant is demonstrated as well. Moreover, the revealed similarity between the SM and phase locked loop (PLL) operations, leads to the conclusion that the algorithms use for analyzing the operation of one may be employed for investigating the other. Experimental results are given to demonstrate the different scenarios, mentioned in the manuscript.

The similarity between unloaded synchronous motor (SM) pull-into-step mechanism and phase locked loop (PLL) synchronization procedure is revealed in this letter. It is shown that both processes possess analogous structure and may therefore be described by same type of equations. As a result, the methodologies used for describing the phase locked loop synchronization may be useful in synchronous motor starting process analysis and vice versa.

The manuscript extends the method of testing the motion controllers’ robustness by emulating uncertainties and disturbances, caused by real loads and mechanical and electrical parameter variations to multiloop motor drives. Such a contribution is important since multiloop drives are widely used in the industrial environment. The proposed technique requires neither connecting physical load nor actually changing any parameter of the electric drive under test. The microprocessor of the motor drive itself creates the effect of the load torque and parameter variations by applying equivalent feed-forward commands to the corresponding loop controller using digital signal processing software. As a result, the electric drive is virtually perturbed, and the controllers’ behavior resembles the performance of a really perturbed drive controllers. The present method, which can be related to a class of Hardware-in-the-Loop Simulations, can be used to test the implementation of robust control algorithms or at didactic purposes using motion control kits found on the market. Simulations and experimental results validate the proposed algorithm, applied to a Brushless DC motor drive, demonstrating an excellent agreement.

A method that allows emulation of parameter uncertainties and external disturbances without any mechanical and electrical parts supplementary to the electric drive is proposed. The emulating signal reflecting the desired changes is created in software and added to the nominal controller output, forcing the unperturbed motor output to resemble the output of a motor with actual uncertainties and disturbances. The proposed method allows simultaneous emulation of any combination of parameter variations and unpredicted disturbances. The method can be related to a class of advanced hardware-in-the-loop simulations, where the nominal hardware is present in the test bed in addition to the controller. The technique can be used to thoroughly test the performance of advanced control algorithms before mass production or for didactic purposes in an educational laboratory using motion control kits found on the market. Simulation and experimental results are reported to prove the feasibility of the proposed approach.

The paper deals with the general analysis of one part of the electromagnetic compatibility (EMC) problem – the electromagnetic coupling applied in the field of power electrical systems. Theoretical analysis of above mentioned problem, based on the impact investigation of the electromagnetic wave propagation, is described in part I. Obtained results can be used for predictive stating of EMC quality of individual new electrotechnical products.

This work presents a simple method to obtain effects similar to those obtained by real mechanical loading and real inertia variation but without any mechanical parts supplementary to the electric motor of the studied electric drive. The electric motor itself produces the load torque and the inertia variation using digital signal processing software. Therefore, the electric drive is virtually torque and inertia loaded, while its behavior is similar to that of the actual loaded drive. The present method could be used to test the implementation of control algorithms or for didactic purposes using motion control kits found on the market. The present method is used with laboratory works of the DSP Fundamentals in power electronics course at the Department of Electrical and Computer Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel.

The paper proposes a novel dual-winding active magnetic energy harvester (D-AMEH), clamped around single power line conductor carrying AC currents with time-varying magnitude while supplying a constant power DC load via an uncontrolled rectifier (e.g., 24/7 aerial marker ball lighting). To allow continuous power flow to the load despite intermittent nature of power line current magnitude, an energy storage unit (rechargeable battery) is integrated into the system via an additional secondary winding, creating an AC-coupled, isolated hybrid energy system with completely decoupled battery and load voltages. The D-AMEH simultaneously harvests the maximum power from the current-carrying conductor and feeds the load with constant power, letting the battery to seamlessly match the difference between harvested and consumed power. Analytical expressions for system currents and voltages are developed, followed by conversion losses estimation. The revealed findings are accurately supported by experiments, demonstrating close matching with corresponding analytical predictions.

This article reveals issues with operation of practical current source fed phase shift controlled semi-active rectifier (PS-ZVS SAR), often utilized as the output stage of resonant converters functioning in the load-independent output current mode. Active rectifier (AR) adoption allows attaining load matching or dc output regulation capabilities. In this work, the operation of a practical PS-ZVS SAR is revisited taking into account output capacitances of switching devices in order to derive lower and upper bounds of attainable output dc current and phase shift angle. Furthermore, measurement and computational delay imposed by digital implementation are also considered for accurate prediction of practical system behavior. According to the findings, voltage transients caused by parasitic capacitances of semiconductor devices and digital delays narrow the feasible phase shift angle region. In order to validate the presented material, series-series compensated wireless power transfer (WPT) system employing PS-ZVS SAR as a receiving-side rectifier is studied as an example. The analytical framework is shown to be accurately supported by both simulations and experiments.

This paper presents novel analytical formulations for Line-voltage Total Harmonic Distortion (LTHD) in three-phase Cascaded H-bridge (CHB) Multilevel Inverters with variable DC supply ratios. While LTHD minimization has been well-studied for fundamental-frequency modulation techniques, this work extends such optimization to high-frequency Pulse Width Modulation (PWM) schemes, specifically the popular sine-PWM (SPWM) and Third Harmonic injection sine-PWM (THISPWM).
Comprehensive LTHD expressions for fixed (symmetric) and variable (asymmetric) DC source ratios were developed using time-domain-based asymptotic analysis. These formulations enable Optimal Minimization of LTHD (OMLTHD) for both modulation techniques. The proposed approach is validated through theoretical analysis, digital simulations across multiple voltage levels (N = 5, 7, 9, 11), and hardware-in-the-loop experiments for a 7-level inverter. Results demonstrate significant LTHD improvements, particularly in challenging low and medium Modulation Index (MI) ranges, achieving relative LTHD reductions of 3.5 % and 75 % compared to conventional SPWM for MI values of 1.0 and 0.1, respectively. MATLAB functions implementing these THD expressions are provided as supplementary material.

The paper presents a methodology for determining the minimum split DC link capacitance for a family of three-phase, three-level grid-connected bidirectional AC-DC converters operating under arbitrary power factor under restriction of DC-only zero-sequence injection. The approach is based on the recently revealed generalized behavior of split DC link voltages in the above-mentioned converters family while distinguishing between leading and lagging power factors in order to highlight different impacts on split DC link capacitor voltages pulsating components. The minimum capacitance value is derived from the boundary condition, ensuring the mains voltage remains below or equal to the capacitor voltage at all times. It is revealed that operation with the lowest expected leading power factor should be employed as the design operating point. The accuracy of the proposed methodology is validated by simulations and experiments carried out employing a 10 kVA grid-connected T-type converter prototype. The results demonstrate close agreement between theoretical predictions and experiments, confirming the practical applicability of the proposed method.

Envelope modeling is an efficient way to obtain the large-signal amplitude and phase dynamics of fast-varying sinusoidal signals required for, e.g., resonant frequency tracking or energy transfer rate regulation in power converters. In addition, the method eliminates fast-varying parameters from the model so that the simulation time and memory requirements are reduced. This paper reveals the envelope-modeling process of a capacitor-powered resonant inverter feeding a time-varying series RLC load, often employed in pulsed-power applications. Such an arrangement is nontrivial since the system does not reach a steady state within a single pulse duration. Furthermore, model order reduction is carried out without performing linearization due to large variations in the expected operation point. As a result, a reduced-order nonlinear envelope model is derived and validated by simulations. Both the proposed modeling method and the derived model aim to simplify the challenging task of feedback controller design.

The paper focuses on linearization of split DC link voltage dynamics and balancing their respective average values in three-phase three-level AC/DC converters. It was recently demonstrated that both AC-side current magnitude and operating power factor impact the dynamics of partial DC link voltage difference, imposing the time-varying behavior of split DC link voltages when a typical linear time-invariant compensator, e.g., proportional or proportional–integrative, is utilized. Consequently, robust split DC link voltage balancing loops would be beneficial. The case of a bandwidth-restricted (DC in a steady state) zero-sequence component employed as a control signal to equalize average partial DC link voltages is considered in this work. It is proposed to nominalize the dynamics of partial DC link voltage difference by means of a linear disturbance observer based on a frequency-selective filter so that the modified dynamics become linear and nearly nominal from a compensator point of view. As a result, the closed-loop response becomes time-invariant—a desirable characteristic of any practical system. Simulations validate the proposed methodology applied to a 10 kVA T-type converter model.

In many practical applications, such as electric vehicle charging and smart transformers, reverse power flow is significantly lower than forward power flow. Designing a full-rated bidirectional DC/DC converter in such cases leads to increased hardware costs. To address this, recent research has explored isolated topologies that support asymmetrical bidirectional power flow at reduced cost. This manuscript investigates an asymmetrical bidirectional DC/DC (AB-DC/DC) converter that integrates a partial-scale active bridge and a partial-scale diode bridge connected in parallel on the secondary side. Passive power sharing between these bridges is controlled by selecting appropriate coupling inductors, but practical magnetic tolerances cause power imbalances. To mitigate this, a novel modulation technique is proposed to enable active power sharing, allowing power transfer from the diode bridge to the active bridge. The study covers various operating regions, including discontinuous conduction mode (DCM), continuous conduction mode (CCM), dual-active-bridge (DAB) mode, and two hybrid regions, where the diode bridge operates in DCM and the active bridge in CCM. Closed-form power expressions and boundary conditions are derived for all modes. The proposed strategy is validated through simulations and experimental measurements on a hardware prototype, demonstrating consistent waveform behavior and confirming the feasibility of active power transfer from the diode bridge to the active bridge.

Capacitor-powered resonant inverters are often employed in pulsed-power applications to feed an equivalent series resistance–inductance–capacitance (RLC) load with time-varying component values. Establishing the short-time dynamics of such an arrangement is nontrivial since the system does not reach a steady state within a single pulse period. As a result, linearization around a single operation point cannot be applied for the sake of simplified system modeling. Consequently, the design of feedback controllers for such systems (aiming for, e.g., resonant frequency tracking or energy transfer rate regulation) is highly cumbersome and challenging since a linear time-invariant regulator is unable to bring the system to desired performance within the whole expected operation range. To cope with the modeling task, a reduced-order envelope model of a capacitor-fed resonant inverter feeding a time-varying RLC load was recently proposed by the authors. In this paper, this model is further simplified and split into linear and nonlinear parts, allowing the employment of a combination of feedback linearizing (nonlinear) action with a linear time-invariant regulator to form a nonlinear control structure allowing the attainment of resonant frequency tracking within a wide operation range. The proposed controller design methodology is accurately validated by multiple time-domain simulations.

In order to optimize the performance of direct (or perturbative) fixed-step maximum power point tracking algorithms (e.g., perturb and observe and incremental conductance), two design parameters-perturbation frequency and step size-must be selected. The main requirement for perturbation frequency design is ensuring the period between two successive perturbations is longer than settling time of photovoltaic generator power transient. According to existing design guidelines, perturbation frequency should be selected at maximum power point, corresponding to standard test conditions. However, due to finite resolution of digital controllers, maximum power region rather than single maximum power point exists in practice. Therefore, operating point can arbitrarily reside within this region, belonging either to constant-current or constant-voltage I-V curve parts. It is shown that the photovoltaic generator power transient settling process is significantly slower in constant current than maximum power region due to increased value of dynamic resistance. Consequently, perturbation frequency design should be carried out in constant-current region rather than at maximum power point. Short-circuit condition should be selected as worst-case design operation point, where photovoltaic generator dynamic resistance obtains highest value. Then, perturbation frequency design becomes photovoltaic generator independent, influenced only by interfacing converter component values. Experimental results validate presented findings successfully.

In this paper, a method for suppressing the low-frequency portion of dc-link ripple inevitably present in power conversion systems with reduced capacitance is proposed. The discussed active capacitance reduction circuitry (consisting of a feedback-controlled shunt-connected bidirectional buck-boost converter, terminated by a small auxiliary capacitance) directly regulates the dc-link voltage, utilizing a dual-loop control structure with parallel-connected multiresonant-bank-enhanced voltage loop stabilizing controller to achieve nearly constant, low-frequency-ripple-free steady-state dc-link voltage. Consequently, the proposed active capacitance reduction system may be perceived as a virtual infinite capacitor from the dc link point of view. The suggested circuitry is successfully applied to a single-phase commercial power factor correction front end in a nearly plug-and-play fashion. The control algorithm effectiveness is fully supported by simulations and experimental results.

The control algorithm based on the uncertainty and disturbance estimator (UDE) is a robust control strategy and has received wide attention in recent years. In this paper, the two-degree-of-freedom nature of UDE-based controllers is revealed. The set-point tracking response is determined by the reference model, whereas the disturbance response and robustness are determined by the error feedback gain and the filter introduced to estimate the uncertainty and disturbances. It is also revealed that the error dynamics of the system is determined by two filters, of which one is determined by the error feedback gain and the other is determined by the filter introduced to estimate the uncertainty and disturbances. The design of these two filters are decoupled in the frequency domain. Moreover, after introducing the UDE-based control, the Laplace transform can be applied to some time-varying systems for analysis and design because all the time-varying parts are lumped into a signal. It has been shown that, in addition to the known advantages over the time-delay control, the UDE-based control also brings better performance than the time-delay control under the same conditions. Design examples and simulation results are given to demonstrate the findings.

In this paper, the reason for operational instability occurring upon neutral line disconnection and reconnection of active three-phase three-level neutral-point-clamped power factor correction rectifiers is revealed and simple solution allowing to maintain correct operation is proposed. It is shown that the neutral line disconnection/reconnection inverts the sign of the partial dc-link voltages balancing loop; thus, reversing the sign of zero-sequence component created by the balancing loop controller would eliminate the mentioned drawback by keeping the balancing loop negative feedback. The proposed finding is experimentally verified on a commercial 25-kVA NPC-PFC front end.

Linear robust controller design based on Uncertainty and Disturbance Estimator theory for nonlinear uncertain single-input single-output systems with external disturbances is discussed in the paper with application to the output voltage control of a unidirectional universal multimode buck/boost/buck–boost converter. The converter is characterized by different nonlinear static and dynamic behaviour in each of the operating modes. The proposed controller forces the system to maintain nearly nominal performance through the whole range of operation space by appropriately estimating and cancelling the terms including nonlinearities, parametric uncertainties and external disturbances. In addition, measurement noise is included in the analysis to demonstrate the trade-offs of the proposed method. Despite the non-triviality and relative complexity of the method, the resulting controller structure is simple, allowing low-cost, low-part-count analogue implementation. Extended simulation results are presented to demonstrate the effectiveness of the proposed control approach.

The application of constant power control and inclusion of energy storage in grid-connected photovoltaic (PV) energy systems may increase the use of two-stage system structures composed of DC–DC-converter-interfaced PV generator and grid-connected inverter connected in cascade. A typical PV-generator-interfacing DC–DC converter is a boost-power-stage converter. The renewable energy system may operate in three different operation modes—grid-forming, grid-feeding, and grid-supporting modes. In the last two operation modes, the outmost feedback loops are taken from the input terminal of the associated power electronic converters, which usually does not pose stability problems in terms of their input sources. In the grid-forming operation mode, the outmost feedback loops have to be connected to the output terminal of the associated power electronic converters, and hence the input terminal will behave as a negative incremental resistor at low frequencies. This property will limit the operation of the PV interfacing converter in either the constant voltage or constant current region of the PV generator for ensuring stable operation. The boost-power-stage converter can be applied as a voltage or current-fed converter limiting the stable operation region accordingly. The investigations of this paper show explicitly that only the voltage-fed mode would provide feasible dynamic and stability properties as a viable interfacing converter.

Voltage-type sources have dominated as an input source for power electronics converters for a long type. The existence of duality implies that there are also current-type sources. The growing application of renewable energy sources such as wind and solar energy has evidently shown that the current-type input sources exist in reality such as photovoltaic (PV) generator or the feedback technique used in controlling the power electronics converters in the renewable energy systems changes the power electronic converters to behaving as such. The recent research on renewable energy systems has indicated that the current-type input sources are very challenging input sources affecting the dynamics of the interfacing converters profoundly. This paper provides a comprehensive survey of the effects of the PV generator on the dynamic behavior of the corresponding interfacing power electronic converters.

Uninhabited electric vehicle typically utilize batteries as an exclusive power source. In order to remedy the limited energy density and thus operation time of the battery-powered unmanned vehicles, fuel based range extenders are often utilized. The operation strategy for the range extender is to maximize the mission endurance therefore it should operate at minimum specific fuel consumption point. Furthermore, the source and load voltage level may differ, hence non-inverting Buck-Boost converter (NBC) is conjoint them while keeping the desire operation point. This paper proposes a fuel cell (FC) based range extender, interfaced to the main power bus by cascade output power regulation strategy for NBC. The NBC is based on unique modulator that produces switching sequence for both converter legs. The modulator receive single control input from the dual loop regulator, inner inductor current loop and outer output power loop, which is common for energy management strategies of hybrid energy sources. System design commences with regulator design based on small signal analysis of NBC, and then it is shown that the suggested control architecture allows tight output power control throughout the entire operating range despite various plants. Finally a case study is presented, in which the converter operates as power processing interface of a fuel cell, operating as range extender in an all-electrical aircraft. The revealed findings are well-supported by simulation and experimental results.

This paper presents a method of battery/supercapacitor emulator (BSE) rapid prototyping, based on modified off-the-shelf components. Low-cost commercial constant output voltage switching power supply, transformed into an input-voltage-controlled converter, is utilized as emulator power stage. The control over input voltage of the power supply is gained by appropriately altering the voltage feedback branch of the control circuitry. Consequently, it becomes possible to tightly regulate the input voltage of the device according to a predefined current–voltage relation and hence emulate any static and/or dynamic behavior by sensing the input current of the power supply and varying its input voltage appropriately. For battery or supercapacitor emulation, the desired charging characteristics may be either derived from manufacturer provided datasheet, obtained experimentally or estimated by solving the appropriate electrical equivalent circuit of the emulated storage device. In order to demonstrate the validity of the proposed method, a prototype was designed and built using an off-the-shelf boost dc–dc converter-based low-cost power supply. Dynamic input characteristics of the prototype were experimentally evaluated and two commercial storage devices (namely MR-2791 lithium ion battery and Maxwell BMOD0058-E016-B02 supercapacitor packs) charging sequences were emulated. The resulting I–V input relations were shown to closely resemble the charging behavior of real devices.

In this paper, design of a capacitor semiactive hybrid source for powering pulsed power loads based on dc power filter principle is presented. The system consists of an energy source connected directly to a load, supported by a bidirectional buck-boost dc-dc converter interfaced supercapacitor (SC). The converter is controlled such that the SC supplies the dynamic component of the load power, leaving the energy source to supply a near-constant power to satisfy average load demand. The control algorithm is adopted from the power filter theory, allowing to reduce the stress of an energy rich source despite operating under a high-power demanding load. Moreover, the SC-load voltage matching is not required and the control algorithm does not require load current sensing. Instead, energy source current of a much lower amplitude is necessary. The SC sizing methodology is proposed, and topology issues aiming to minimize the SC are discussed as well. Compared with a passive hybrid, the proposed system utilizes much lower capacitance at the expense of additional power electronics. Experimental results are presented to demonstrate the feasibility of the approach.

In this paper, design process and functionality of a portable single-panel dual-battery solar charger prototype are presented, achieving energy density of 571 Wh/kg during a typical 3-day infantry mission. The device may instantaneously charge up to two Li-ion MR-2791 batteries, supporting plug-and-play operation. The system consists of a lightweight custom solar panel, based on 20% efficient monocrystalline photovoltaics, and an intelligent power processing module. The panel contains eight transparent polymer-encapsulated and camouflaged series-connected six solar cell packs with antiparallel diodes, allowing partial shading operation. The power processing module consists of two synchronous current-mode-controlled buck converters, digital signal processor, and a microcontroller, supporting both maximum power point tracking of the solar panel with partial shading detection and multimode charging of Li-ion packs while instantaneously communicating with the batteries. Power management algorithmic design is presented, based on ensuring system stability while supporting the required operation modes. System implementation stages and underlying issues are thoroughly discussed, and utilized hardware components are presented in detail. Experimental results of system testing under real outdoor conditions are presented to demonstrate the device functionality and energy yield capabilities.

Stationary reference frame proportional-resonant (PR) controllers have recently became a viable alternative to rotation reference frame proportional-integrative compensators in ac applications because of their ability of achieving zero steady-state error without the need for computational-intensive reference frame transformations. While extensive efforts have been put into performance comparison of the two control schemes, design of PR controllers according to desired closed-loop time-domain transient performance was barely investigated. This letter proposes a method for deriving PR controller structure and coefficients according to desired transient behavior of ac signal amplitude, applied to typical power converter current loop. The method is based on the fact that if ac signal envelope is perceived as dc signal, its transient behavior may be easily shaped utilizing well-known approaches employed in dc systems loop shaping while keeping zero phase tracking error at all times. On the other hand, while desired transient performance is easily achieved, the relation between crossover frequency and transient processes time constant is not as straightforward as in dc systems. The validity of the presented theoretical analysis is evaluated by simulations.

In this paper, a robust control method based on a disturbance observer is proposed to regulate the terminal voltage of a photovoltaic generator, interfaced by a current mode-controlled boost dc-dc converter. The combined generator-converter-load system possesses a nonlinear behavior, highly dependent on operation point and environmental variables, thus burdening the control task. It is shown that employing a typical linear controller, designed according to a single nominal operating point, results in a closed-loop performance, varying from a highly overdamped near open-circuit condition to greatly underdamped around short-circuit conditions. On the other hand, when the proposed robust controller is utilized, the closed-loop performance remains nearly nominal throughout the whole operation range. In addition, it is shown that, by sacrificing the performance in the vicinity of the open-circuit point, it is possible to implement the controller using a single op-amp with a reduced part count. Simulation and experimental results are presented to verify the proposed method.

Nonlinear characteristics of photovoltaic generators were recently shown to significantly influence the dynamics of interfacing power stages. Moreover, since the dynamic resistance of photovoltaic generators is both operating point and environmental variables dependent, the combined dynamics exhibits these dependencies as well, burdening control challenge. Typically, linear time invariant input voltage loop controllers (e.g. Proportional-Integrative-Derivative) are utilized in photovoltaic applications, designed according to nominal operating conditions. Nevertheless, since actual dynamics is seldom nominal, closed loop performance of such systems varies as well. In this paper, adaptive control method is proposed, allowing to estimate photovoltaic generator resistance online and utilize it to modify the controller parameters such that closed loop performance remains nominal throughout the whole operation range. Unlike previously proposed method, utilizing double-grid-frequency component for estimation purposes and suffering from various drawbacks such as operation point dependence and applicability to single-phase grid connected systems only, the proposed method is based on harmonic current injection and is independent on operating point and system topology.

In this paper, “An Efficient Partial Power Processing DC/DC Converter for Distributed PV Architectures” by Agamy et al. (IEEE Trans. Power Electron., vol. 29, no. 2, Feb. 2014), a dc–dc converter for distributed photovoltaic plant architectures, capable of performing series-type partial power processing under maximum power point control was proposed and tested for various performance parameters. The purpose of this note is correcting (IEEE Trans. Power Electron., vol. 29, no. 2, Feb. 2014) by proving that while the overall operation and results are technically correct, the proposed converter is actually a boost stage performing full rather than partial power processing.

This paper investigates the dynamic properties of the photovoltaic-generator-interfacing voltage-controlled buck power stage operating in both the maximum and limited power point tracking modes. The photovoltaic generator (PVG) is known to possess both current- and voltage-source properties with respect to its maximum power point. While voltage-fed operation is conventional, current-fed action is nontrivial and is thoroughly analyzed in this paper. The photovoltaic-generator-interfacing converter is formed by adding a capacitor at conventional voltage-fed converter input terminals, turning it into a current-fed power stage. During the maximum power point tracking phase, converter input voltage is regulated, possessing nontrivial dynamics. The situation is burdened further when output-voltage control should be alternatively realized to limit the voltage of the converter terminating the energy storage element. It is shown that both the photovoltaic generator and the terminating energy storage greatly affect the combined system dynamics. Parallel as well as cascaded control arrangements are proposed to support dual-mode system operation. Extended experimental results are shown to enforce presented theory and reveal nontrivial dynamics-related issues.

A pulse-width modulation modulator for a noninverting bidirectional buck–boost converter is analyzed and a corresponding average-mode current controller design is revealed. The main feature of the modulator is the ability to create switching sequences for both converter legs without requiring any information regarding either operation mode or the direction of power flow. The modulator receives a control signal generated by the current controller, and a triangular carrier and generates driving signals with two different duty cycles, allowing tight control of the inductor current throughout the entire operating range. The underlying circuitry is thus relatively simple; moreover, the proposed method greatly simplifies the outer loop controller design. The revealed findings are supported by simulations and experiments.

In transformer-less grid-connected renewable energy systems, interfacing of photovoltaic (PV) generators is typicallyimplemented by means of DC–DC boost-power-stage converter, mainly because of its voltage-boosting capability. In order totrack the maximum power point of a PV generator, input voltage of the converter is usually feedback controlled, forcing theconverter to operate as a current-sourced rather than voltage-sourced converter. Nevertheless, PV generator interfacing powerstage is commonly assumed to possess the same dynamic properties as corresponding voltage-sourced power stage.Investigations presented in this study reveal explicitly that the dynamics of PV generator interfacing DC–DC boost powerstage resembles conventional buck power stage behaviour with duty-cycle independent resonance and additional right-half-plane zeros. In addition, the duty cycle has to be decreased for increasing the corresponding output variables (i.e. inputvoltage and output current). Extended experimental results are given to support the theoretical findings.

The manuscript reveals combined source-converter-load dynamics of interfacing renewable energy generators by means of terminal voltage control, aimed to track a Maximum Power Line. Control-toinput voltage transfer functions are calculated for three basic DC–DC converters based power electronic interfaces operating in both current and voltage control modes; respective stability assessment is performed as well for each arrangement. In order to generalize the derived dynamics, it is shown that photovoltaic and wind generators may be represented by similar electrical equivalent circuits, possessing comparable small-signal dynamics. It is exposed that dynamic impedance of renewable energy generators is both operating point and environmental conditions dependent and hence plays a crucial role in the combined source-converter-load dynamics from affecting system damping to causing openloop instability in particular arrangements. Consequently, special care must be taken when designing power electronic interface intended to operate as a renewable energy generator power processor while at the same time the controller must be robust enough to ensure system stability for all expected environmental conditions. In addition, in case fixed closed-loop behavior is required through the whole operating range of the system, some kind of adaptive mechanism is required to estimate the dynamic impedance online. Several particular case examples of the proposed method presented in the literature are reviewed.

Stationary frame (AC) currents behaviour of three-phase converters with synchronous frame (DC) controllers shaping is explicitly linked. It is revealed that closed-loop synchronous frame dynamics determines amplitude behaviour of stationary frame signals without affecting their frequency and phase. Consequently, synchronous frame current controllers design should actually be based on desired stationary frame amplitude transient performance.

Voltage-type sources such as storage battery, ac grid, and constant-output-voltage-regulated converters have dominated as input sources for power electronic interfaces for a long time, leading to the development of different power stages dedicated to voltage-type input sources. Recent penetration of renewable energy sources has initiated the use of current-type sources as well as input voltage regulated converters as input sources for power electronic interfaces. While the power electronic converter topology remains unchanged in both the cases, steady state and dynamic properties of the coupled source-converter system are quite different. Moreover, the voltage/current nature of the load contributes to the complex dynamics as well. This paper investigates the factors determining the dynamic properties of a power electronic converter in a specific arrangement. The findings show that the open-loop converter (without any internal or external feedbacks) automatically adapts its dynamic properties to the properties stipulated by source and load if certain terminal constraints are satisfied. If internal or external feedback is activated, the dynamic properties of the converter may be varied as desired; however, the control design process is substantially different for each source/load arrangement. The findings presented in this paper have not been presented in the literature by far. A buck-power-stage converter is used as an illustrative example. Experimental results are given to validate the analytic investigation outcomes.

The manuscript presents a method of interfacing renewable energy generators by means of Maximum Power Line tracking rather than Maximum Power Point tracking. The maximum power line connects the maximum power points of output I–V curves of a source for different values of power producing parameter (wind, solar insolation etc.) and may be estimated offline with moderate accuracy. As a result, during the online operation, the maximum power point tracker only has to compensate for maximum power line inaccuracy and changes caused by slow temperature variations and system parameters drift. The approach allows reducing dramatically the bandwidth of the MPP tracking algorithms and simplifying the implementation, making analog MPP trackers a viable choice. The proposed method is shown to be a generalized version of the well-known loss-free resistor concept, referred to as loss-free load in the manuscript. Several particular case examples of the proposed method presented in the literature are reviewed.

This paper presents the functionality of a commercialized fast charger for a lithium-ion electric vehicle propulsion battery. The device is intended to operate in a battery switch station, allowing an up-to 1-h recharge of a 25-kWh depleted battery, removed from a vehicle. The charger is designed as a dual-stage-controlled ac/dc converter. The input stage consists of a three-phase full-bridge diode rectifier combined with a reduced rating shunt active power filter. The input stage creates an uncontrolled pulsating dc bus while complying with the grid codes by regulating the total harmonic distortion and power factor according to the predetermined permissible limits. The output stage is formed by six interleaved groups of two parallel dc-dc converters, fed by the uncontrolled dc bus and performing the battery charging process. The charger is capable of operating in any of the three typical charging modes: constant current, constant voltage, and constant power. Extended simulation and experimental results are shown to demonstrate the functionality of the device.

The paper presents a topological overview of hybrid powertrains for battery-powered vehicles reinforced by range extenders. First, tradeoffs of employing high energy versus high power battery are revealed. Then, different topologies of battery-ultracapacitor hybrids are discussed, highlighting pros and cons of each configuration. The superiority of fully active hybrids is indicated, obtained at the expense of increase of power electronic circuitry, control effort, and efficiency. The second part of the paper focuses on two types of range extenders: renewable energy and fuel-based units. The operation strategy is shown to be different for each range extender type. The renewable-energy-based range extender should be operated employing either passive or active maximum power point tracking strategy and hence not be involved in the powertrain energy balancing. It is shown that such a strategy allows the rest of system to perceive the renewable energy range extender (RERE) as a part of the load and act accordingly. Solar array is given as an example of a RERE and the possible connection topologies are discussed. On the other hand, the fuel-based range extender (FBRE) should be operated near the lowest specific fuel consumption point employing maximum efficiency point tracking strategy. Fuel cells and internal combustion engines are specified as examples of FBREs. The complete powertrain is shown to resemble a dc microgrid with source, storage, and load units connected through power management circuitry to a common dc link.

A new method for capacitance increase is proposed, thus allowing for capacitance standards with a sixfold higher value than those currently found in the market. The method can be used for capacitance increase in any standard and provides a solution for calibration problems of high-capacitance four-terminal meters. The increase in capacitance is based on the introduction of inductive coupling between the current and potential circuits in devices with four electrodes. The output capacitance is created by the summation of the capacitive and inductive parameters that were formed in various channels. The operating frequency range resides at the left of the resonant frequency and is separated from the resonance by a range of frequencies called ¿protective band¿. The limitations on the width of this band and the quality factor are considered in this paper and are discussed in depth. It is shown that standards should be calibrated on each operating frequency when using the proposed method. The uncertainties of the method are also analyzed, and the factors that affect the uncertainty increase are clearly indicated. Simulation and experimental results are presented to verify the proposed method and demonstrate its feasibility.

This paper offers a new approach to analyses of cycloconverter operation. The difference equations describing the cycloconverters’ transient and steady-state operating regimes are derived. Theoretical predictions were validated by a computer program which calculated the load current of different cycloconverter topologies using the proposed methodology. The calculated and experimental results are compared and found to be in good agreement.

The paper deals with the general analysis of one part of the electromagnetic compatibility (EMC) problem – the electromagnetic coupling applied in the field of power electrical systems. Theoretical analysis of above mentioned problem, based on the impact investigation of the electromagnetic wave propagation, is described in part I. Obtained results can be used for predictive stating of EMC quality of individual new electrotechnical products.

A method of rapid prototyping of a solar array simulator, based on low cost, off-the-shelf components is proposed in the paper. A commercial constant output voltage switching power supply is utilized as a power stage. It is shown that it is possible to gain control over output voltage of such a device by injecting variable analog voltage into the voltage feedback loop of the supply. As a result, by sensing the power supply output current and varying the injected voltage it is possible to change the output voltage according to a predefined relation and hence any static I-V curve may be emulated by the device. For simulating a solar array output characteristics, the desired I-V curve may be either digitized from a manufacturer provided datasheet, obtained experimentally or estimated from three basic current-voltage pairs (open circuit, short circuit, and maximum power points) using a dedicated algorithm. In order to demonstrate the proposed method, a prototype was designed and built based on available low-cost commercial components. Dynamic characteristics of the prototype were experimentally evaluated and three static I-V curves of a commercial solar panel were simulated. The resulting I-V output characteristics were shown to closely resemble datasheet I-V curves.

Low throttle operation of internal combustion engine-based auxiliary power units is desirable under light load to decrease specific fuel consumption. Unfortunately, sudden load increase may lead to voltage collapse and consequent stability lost due to limited total inertia and slow prime mover dynamics. This letter demonstrates that connecting a supercapacitor across auxiliary power unit output terminals is equivalent to increasing total inertia and may enhance low throttle operational robustness. Proposed findings are validated by experimental results.

The control algorithm based on the uncertainty and disturbance estimator (UDE) is a robust control strategy and has received wide attention in recent years. In this paper, the two-degree-of-freedom nature of UDE-based controllers is revealed. The set-point tracking response is determined by the reference model, whereas the disturbance response and robustness are determined by the error feedback gain and the filter introduced to estimate the uncertainty and disturbances. It is also revealed that the error dynamics of the system is determined by two filters, of which one is determined by the error feedback gain and the other is determined by the filter introduced to estimate the uncertainty and disturbances. The design of these two filters are decoupled in the frequency domain. Moreover, after introducing the UDE-based control, the Laplace transform can be applied to some time-varying systems for analysis and design because all the time-varying parts are lumped into a signal. It has been shown that, in addition to the known advantages over the time-delay control, the UDE-based control also brings better performance than the time-delay control under the same conditions. Design examples and simulation results are given to demonstrate the findings.

Functional equivalence of three nonmodel-based variable-step-size maximum power point tracking (MPPT) algorithms is revealed in this paper by establishing general closed-loop controller-plant structure of corresponding MPPT control loops, allowing us to formulate the problem as a typical stabilization task. The MPPT loop plants may be separated into three main components, two of which are similar and the third one, namely stabilization function estimator, is the main reason for the performance differences of the discussed methods in case the MPPT loop controllers are alike. It is shown that in case the estimator convergence rate is much faster than the MPPT loop bandwidth, similar low-frequency performance may be expected by utilizing any of the three methods.

This paper presents a method of battery/supercapacitor emulator (BSE) rapid prototyping, based on modified off-the-shelf components. Low-cost commercial constant output voltage switching power supply, transformed into an input-voltage-controlled converter, is utilized as emulator power stage. The control over input voltage of the power supply is gained by appropriately altering the voltage feedback branch of the control circuitry. Consequently, it becomes possible to tightly regulate the input voltage of the device according to a predefined current–voltage relation and hence emulate any static and/or dynamic behavior by sensing the input current of the power supply and varying its input voltage appropriately. For battery or supercapacitor emulation, the desired charging characteristics may be either derived from manufacturer provided datasheet, obtained experimentally or estimated by solving the appropriate electrical equivalent circuit of the emulated storage device. In order to demonstrate the validity of the proposed method, a prototype was designed and built using an off-the-shelf boost dc–dc converter-based low-cost power supply. Dynamic input characteristics of the prototype were experimentally evaluated and two commercial storage devices (namely MR-2791 lithium ion battery and Maxwell BMOD0058-E016-B02 supercapacitor packs) charging sequences were emulated. The resulting I–V input relations were shown to closely resemble the charging behavior of real devices.

Methodology for obtaining realistic supercapacitor (SC) Ragone from manufacturer datasheet only is presented in this letter, allowing to predict long-term wide-temperature SC power and energy performance for given terminal voltage limits. Analytical derivations are based on the simplified RC equivalent SC model, connected to a constant power element, taking into account manufacturer provided age and temperature parameter dependences. The main goal of the proposed approach is to allow practical energy engineer to quickly design a SC pack according to the desired long-term performance without performing further tests or requesting additional data. Simulation and experimental results are presented in order to validate the suggested methodology.

In this paper, design of a capacitor semiactive hybrid source for powering pulsed power loads based on dc power filter principle is presented. The system consists of an energy source connected directly to a load, supported by a bidirectional buck-boost dc-dc converter interfaced supercapacitor (SC). The converter is controlled such that the SC supplies the dynamic component of the load power, leaving the energy source to supply a near-constant power to satisfy average load demand. The control algorithm is adopted from the power filter theory, allowing to reduce the stress of an energy rich source despite operating under a high-power demanding load. Moreover, the SC-load voltage matching is not required and the control algorithm does not require load current sensing. Instead, energy source current of a much lower amplitude is necessary. The SC sizing methodology is proposed, and topology issues aiming to minimize the SC are discussed as well. Compared with a passive hybrid, the proposed system utilizes much lower capacitance at the expense of additional power electronics. Experimental results are presented to demonstrate the feasibility of the approach.

An original ultracapacitor (UC) based compact electric power source is introduced in the paper. The device employs the synergy between rich energy content of vehicle lead-acid batteries and power capabilities of UCs to allow emergency starting of internal combustion engine in case of a weak battery. The UC-based power source is capable of charging at low rate from the battery and then providing current burst required for proper engine starting. A prototype is designed employing original power circuitry, and a dedicated algorithm for optimal UC charging is developed. The device is successfully used for diesel engine starting, as shown by experimental results.

The purpose of the contribution is evaluating the fuel efficiency of gas turbine (GT) engine-based hybrid vehicles, which can be manufactured utilizing modern technologies. An analytical equation for calculating fuel consumption is derived taking into account specific properties of hybrid vehicles. European Union Directives and regulations of the United Nations Economic Commission for Europe are adopted to evaluate the fuel efficiency. The equation is first verified by calculating the mileage of several commercial hybrid passenger vehicles and then applied to GT-based hybrid vehicles. It is revealed that even though GT engine possesses relatively poor efficiency, reduced turbine-generator weight results in a lower overall weight of the vehicle, leading to fuel consumption decrease. The estimated fuel efficiency of GT engine-based vehicles is shown to be on a par with the efficiency of widely employed diesel and gasoline engine-based vehicles.

In this paper, design process and functionality of a portable single-panel dual-battery solar charger prototype are presented, achieving energy density of 571 Wh/kg during a typical 3-day infantry mission. The device may instantaneously charge up to two Li-ion MR-2791 batteries, supporting plug-and-play operation. The system consists of a lightweight custom solar panel, based on 20% efficient monocrystalline photovoltaics, and an intelligent power processing module. The panel contains eight transparent polymer-encapsulated and camouflaged series-connected six solar cell packs with antiparallel diodes, allowing partial shading operation. The power processing module consists of two synchronous current-mode-controlled buck converters, digital signal processor, and a microcontroller, supporting both maximum power point tracking of the solar panel with partial shading detection and multimode charging of Li-ion packs while instantaneously communicating with the batteries. Power management algorithmic design is presented, based on ensuring system stability while supporting the required operation modes. System implementation stages and underlying issues are thoroughly discussed, and utilized hardware components are presented in detail. Experimental results of system testing under real outdoor conditions are presented to demonstrate the device functionality and energy yield capabilities. Copyright © 2015 John Wiley & Sons, Ltd.

In this paper, instantaneous power and energy capabilities of supercapacitor (SC) connected to a power element are derived for an arbitrary power profile, given either in analytical or statistical distribution form. A class of applications is considered where the device is used as deeply cycled energy storage with significant capacity, absorbing/supplying the whole power flow or its significant component rather than shaving low-energy high-frequency peaks. The analytical derivation of SC behavior is based on simple RC model with parameters taken from a manufacturer datasheet. It is shown that the commonly adopted “state-of-charge” indication based on terminal voltage only is insufficient to reflect the energy balance for both charging and discharging; hence an alternative definition of “state-of-energy” is proposed for each direction of energy flow, depending on both instantaneous power and terminal voltage. A simplified quick noniterative sizing procedure is proposed at the expense of a slightly oversized SC. Comprehensive example is provided in order to reinforce the proposed method of analyzing SC performance and demonstrate sizing procedure.

Analytical description of a constant power fed supercapacitor behavior is revealed in the paper. The derivation is based on a simple RC model with parameters taken from a manufacturer datasheet. Different power and energy-related figures of merit are obtained using the derived expressions. It is shown that some of the performance figures used in datasheets are strictly theoretical and cannot be achieved in practice. The process of Ragone plot construction based on the proposed method is described as well. Moreover, it is shown that the upper limit of a supercapacitor voltage imposes certain limits on power and energy capabilities of the device. Extended simulation and experimental results are provided in order to reinforce the proposed method and justify the selected model for describing supercapacitor performance. Appropriate comparison of simulations and experiments shows that the simple first-order model may be utilized to predict supercapacitor behavior with reasonable accuracy to perform an initial design.

Analytical derivation of constant power loaded supercapacitor behavior is presented in the paper. Simple RC model based on manufacturer datasheet extracted parameters is employed. Power and energy related figures of merit are obtained from the derived expressions and compared to the datasheet provided values. It is revealed that some of the performance characteristics provided in most of the datasheets are theoretical and cannot be achieved in practice. The process of a realistic Ragone plot derivation based on the proposed method is described in the paper as well. It is shown that the lower limit of supercapacitor voltage imposes certain limits on power and energy capabilities of the device. Extended simulation and experimental results are provided in order to reinforce the proposed method and justify the selected RC model for describing the supercapacitor performance. By appropriate comparison of simulations and experiments it is proven that the selected model, while being oversimplified and low order, may be used to predict supercapacitor behavior with reasonable accuracy to perform at least an initial design.

An analytical method of evaluating vehicle fuel consumption under standard operating conditions is presented. In the proposed model, vehicle fuel consumption is separated into two different operating modes: cruising at constant speed and acceleration. In each of these modes fuel consumption is calculated based on the instantaneous engine efficiency, approximated using an analytical function rather than typically considered consumption map. The approximation is based on speed-power decoupling, employing two single dimension polynomials instead of a two-dimensional lookup table. The adequacy and accuracy of the model is verified using experimental calculations. Moreover, it is shown that the effect of various design parameters on vehicle fuel consumption can be studied utilizing the proposed model.

The paper presents a topological overview of hybrid powertrains for battery-powered vehicles reinforced by range extenders. First, tradeoffs of employing high energy versus high power battery are revealed. Then, different topologies of battery-ultracapacitor hybrids are discussed, highlighting pros and cons of each configuration. The superiority of fully active hybrids is indicated, obtained at the expense of increase of power electronic circuitry, control effort, and efficiency. The second part of the paper focuses on two types of range extenders: renewable energy and fuel-based units. The operation strategy is shown to be different for each range extender type. The renewable-energy-based range extender should be operated employing either passive or active maximum power point tracking strategy and hence not be involved in the powertrain energy balancing. It is shown that such a strategy allows the rest of system to perceive the renewable energy range extender (RERE) as a part of the load and act accordingly. Solar array is given as an example of a RERE and the possible connection topologies are discussed. On the other hand, the fuel-based range extender (FBRE) should be operated near the lowest specific fuel consumption point employing maximum efficiency point tracking strategy. Fuel cells and internal combustion engines are specified as examples of FBREs. The complete powertrain is shown to resemble a dc microgrid with source, storage, and load units connected through power management circuitry to a common dc link.

Battery versus hybrid power sources performance is examined in the manuscript. Passive, semi-active and fully active battery–ultracapacitor hybrids show obvious superiority over battery only powered pulsed current loads. Passive hybrid is the most simple and cheap arrangement, however its uncontrolled nature results in several drawbacks during the operation. On the other hand, the fully active hybrids achieve superior performance at the expense of two DC–DC converters and the corresponding control circuitry. The trade off between the topologies is the semi-active hybrid, employing only one DC–DC converter and attaining a compromising performance. The thorough characterization of each topology and sub-topology is presented in the manuscript and design methodology is derived for a particular case of pulsed current load.

A Fourier-based analysis of passive battery–ultracapacitor hybrid sources is introduced in the manuscript. The approach is first introduced for a general load, and then is followed by a study for a case of periodic pulsed current load. It is shown that the ultracapacitor branch is perceived by the battery as a low-pass filter, which absorbs the majority of the high frequency harmonic current and letting the battery to supply the average load demand in addition to the small part of dynamic current. Design requirements influence on the ultracapacitor capacitance and internal resistance choice are quantitatively discussed. The theory is enforced by simulation and experimental results, showing an excellent agreement.

In this paper, analytical investigation of an actively balanced open-loop operated supercapacitor bank is presented. Supercapacitor unit is utilized for 28 V auxiliary power unit diesel engine starting, allowing relieving the battery from multiple starting stresses. Dynamical equations of the system based on a synchronous bidirectional buck-boost converter are developed by splitting the solution into zero-input and zero-state responses. It is revealed that the system, which is typically nonlinear because of buck-boost converter presence, becomes linear when operated in open loop. Moreover, natural balancing is achieved when the converter is operated with 50% duty cycle. It is shown that balancing time is independent on initial conditions while system damping strongly depends on parasitic resistances especially in practical case of large capacitors and small inductance. Inductor current peak value and balancing time are obtained analytically and validated by simulations. It is revealed that while natural balancing is always achieved, excessive currents may arise when the initial voltage misbalance is significant. In addition, it is shown that one-switching-cycle averaged model is in close agreement with detailed switched model. The presented findings are fully supported by extended simulations

In order to optimize the performance of direct (or perturbative) fixed-step maximum power point tracking algorithms (e.g., perturb and observe and incremental conductance), two design parameters-perturbation frequency and step size-must be selected. The main requirement for perturbation frequency design is ensuring the period between two successive perturbations is longer than settling time of photovoltaic generator power transient. According to existing design guidelines, perturbation frequency should be selected at maximum power point, corresponding to standard test conditions. However, due to finite resolution of digital controllers, maximum power region rather than single maximum power point exists in practice. Therefore, operating point can arbitrarily reside within this region, belonging either to constant-current or constant-voltage I-V curve parts. It is shown that the photovoltaic generator power transient settling process is significantly slower in constant current than maximum power region due to increased value of dynamic resistance. Consequently, perturbation frequency design should be carried out in constant-current region rather than at maximum power point. Short-circuit condition should be selected as worst-case design operation point, where photovoltaic generator dynamic resistance obtains highest value. Then, perturbation frequency design becomes photovoltaic generator independent, influenced only by interfacing converter component values. Experimental results validate presented findings successfully.

The application of constant power control and inclusion of energy storage in grid-connected photovoltaic (PV) energy systems may increase the use of two-stage system structures composed of DC–DC-converter-interfaced PV generator and grid-connected inverter connected in cascade. A typical PV-generator-interfacing DC–DC converter is a boost-power-stage converter. The renewable energy system may operate in three different operation modes—grid-forming, grid-feeding, and grid-supporting modes. In the last two operation modes, the outmost feedback loops are taken from the input terminal of the associated power electronic converters, which usually does not pose stability problems in terms of their input sources. In the grid-forming operation mode, the outmost feedback loops have to be connected to the output terminal of the associated power electronic converters, and hence the input terminal will behave as a negative incremental resistor at low frequencies. This property will limit the operation of the PV interfacing converter in either the constant voltage or constant current region of the PV generator for ensuring stable operation. The boost-power-stage converter can be applied as a voltage or current-fed converter limiting the stable operation region accordingly. The investigations of this paper show explicitly that only the voltage-fed mode would provide feasible dynamic and stability properties as a viable interfacing converter.

Voltage-type sources have dominated as an input source for power electronics converters for a long type. The existence of duality implies that there are also current-type sources. The growing application of renewable energy sources such as wind and solar energy has evidently shown that the current-type input sources exist in reality such as photovoltaic (PV) generator or the feedback technique used in controlling the power electronics converters in the renewable energy systems changes the power electronic converters to behaving as such. The recent research on renewable energy systems has indicated that the current-type input sources are very challenging input sources affecting the dynamics of the interfacing converters profoundly. This paper provides a comprehensive survey of the effects of the PV generator on the dynamic behavior of the corresponding interfacing power electronic converters.

Uninhabited electric vehicle typically utilize batteries as an exclusive power source. In order to remedy the limited energy density and thus operation time of the battery-powered unmanned vehicles, fuel based range extenders are often utilized. The operation strategy for the range extender is to maximize the mission endurance therefore it should operate at minimum specific fuel consumption point. Furthermore, the source and load voltage level may differ, hence non-inverting Buck-Boost converter (NBC) is conjoint them while keeping the desire operation point. This paper proposes a fuel cell (FC) based range extender, interfaced to the main power bus by cascade output power regulation strategy for NBC. The NBC is based on unique modulator that produces switching sequence for both converter legs. The modulator receive single control input from the dual loop regulator, inner inductor current loop and outer output power loop, which is common for energy management strategies of hybrid energy sources. System design commences with regulator design based on small signal analysis of NBC, and then it is shown that the suggested control architecture allows tight output power control throughout the entire operating range despite various plants. Finally a case study is presented, in which the converter operates as power processing interface of a fuel cell, operating as range extender in an all-electrical aircraft. The revealed findings are well-supported by simulation and experimental results.

Functional equivalence of three nonmodel-based variable-step-size maximum power point tracking (MPPT) algorithms is revealed in this paper by establishing general closed-loop controller-plant structure of corresponding MPPT control loops, allowing us to formulate the problem as a typical stabilization task. The MPPT loop plants may be separated into three main components, two of which are similar and the third one, namely stabilization function estimator, is the main reason for the performance differences of the discussed methods in case the MPPT loop controllers are alike. It is shown that in case the estimator convergence rate is much faster than the MPPT loop bandwidth, similar low-frequency performance may be expected by utilizing any of the three methods.

In this paper, design process and functionality of a portable single-panel dual-battery solar charger prototype are presented, achieving energy density of 571 Wh/kg during a typical 3-day infantry mission. The device may instantaneously charge up to two Li-ion MR-2791 batteries, supporting plug-and-play operation. The system consists of a lightweight custom solar panel, based on 20% efficient monocrystalline photovoltaics, and an intelligent power processing module. The panel contains eight transparent polymer-encapsulated and camouflaged series-connected six solar cell packs with antiparallel diodes, allowing partial shading operation. The power processing module consists of two synchronous current-mode-controlled buck converters, digital signal processor, and a microcontroller, supporting both maximum power point tracking of the solar panel with partial shading detection and multimode charging of Li-ion packs while instantaneously communicating with the batteries. Power management algorithmic design is presented, based on ensuring system stability while supporting the required operation modes. System implementation stages and underlying issues are thoroughly discussed, and utilized hardware components are presented in detail. Experimental results of system testing under real outdoor conditions are presented to demonstrate the device functionality and energy yield capabilities.

Nonlinear characteristics of photovoltaic generators were recently shown to significantly influence the dynamics of interfacing power stages. Moreover, since the dynamic resistance of photovoltaic generators is both operating point and environmental variables dependent, the combined dynamics exhibits these dependencies as well, burdening control challenge. Typically, linear time invariant input voltage loop controllers (e.g. Proportional-Integrative-Derivative) are utilized in photovoltaic applications, designed according to nominal operating conditions. Nevertheless, since actual dynamics is seldom nominal, closed loop performance of such systems varies as well. In this paper, adaptive control method is proposed, allowing to estimate photovoltaic generator resistance online and utilize it to modify the controller parameters such that closed loop performance remains nominal throughout the whole operation range. Unlike previously proposed method, utilizing double-grid-frequency component for estimation purposes and suffering from various drawbacks such as operation point dependence and applicability to single-phase grid connected systems only, the proposed method is based on harmonic current injection and is independent on operating point and system topology.

This paper investigates the dynamic properties of the photovoltaic-generator-interfacing voltage-controlled buck power stage operating in both the maximum and limited power point tracking modes. The photovoltaic generator (PVG) is known to possess both current- and voltage-source properties with respect to its maximum power point. While voltage-fed operation is conventional, current-fed action is nontrivial and is thoroughly analyzed in this paper. The photovoltaic-generator-interfacing converter is formed by adding a capacitor at conventional voltage-fed converter input terminals, turning it into a current-fed power stage. During the maximum power point tracking phase, converter input voltage is regulated, possessing nontrivial dynamics. The situation is burdened further when output-voltage control should be alternatively realized to limit the voltage of the converter terminating the energy storage element. It is shown that both the photovoltaic generator and the terminating energy storage greatly affect the combined system dynamics. Parallel as well as cascaded control arrangements are proposed to support dual-mode system operation. Extended experimental results are shown to enforce presented theory and reveal nontrivial dynamics-related issues.

The letter reveals that when low-frequency dynamics of a wind turbine generator are reflected to the load side, the resulting electrical equivalent circuit is similar to a typical solar generator equivalent circuit. The finding allows drawing a parallel between the corresponding energy conversion processes, as well as applying advanced methods of analyzing and controlling photovoltaic generators to interfacing wind turbine generators.

In transformer-less grid-connected renewable energy systems, interfacing of photovoltaic (PV) generators is typicallyimplemented by means of DC–DC boost-power-stage converter, mainly because of its voltage-boosting capability. In order totrack the maximum power point of a PV generator, input voltage of the converter is usually feedback controlled, forcing theconverter to operate as a current-sourced rather than voltage-sourced converter. Nevertheless, PV generator interfacing powerstage is commonly assumed to possess the same dynamic properties as corresponding voltage-sourced power stage.Investigations presented in this study reveal explicitly that the dynamics of PV generator interfacing DC–DC boost powerstage resembles conventional buck power stage behaviour with duty-cycle independent resonance and additional right-half-plane zeros. In addition, the duty cycle has to be decreased for increasing the corresponding output variables (i.e. inputvoltage and output current). Extended experimental results are given to support the theoretical findings.

In this paper, design process and functionality of a portable single-panel dual-battery solar charger prototype are presented, achieving energy density of 571 Wh/kg during a typical 3-day infantry mission. The device may instantaneously charge up to two Li-ion MR-2791 batteries, supporting plug-and-play operation. The system consists of a lightweight custom solar panel, based on 20% efficient monocrystalline photovoltaics, and an intelligent power processing module. The panel contains eight transparent polymer-encapsulated and camouflaged series-connected six solar cell packs with antiparallel diodes, allowing partial shading operation. The power processing module consists of two synchronous current-mode-controlled buck converters, digital signal processor, and a microcontroller, supporting both maximum power point tracking of the solar panel with partial shading detection and multimode charging of Li-ion packs while instantaneously communicating with the batteries. Power management algorithmic design is presented, based on ensuring system stability while supporting the required operation modes. System implementation stages and underlying issues are thoroughly discussed, and utilized hardware components are presented in detail. Experimental results of system testing under real outdoor conditions are presented to demonstrate the device functionality and energy yield capabilities. Copyright © 2015 John Wiley & Sons, Ltd.

The manuscript reveals combined source-converter-load dynamics of interfacing renewable energy generators by means of terminal voltage control, aimed to track a Maximum Power Line. Control-toinput voltage transfer functions are calculated for three basic DC–DC converters based power electronic interfaces operating in both current and voltage control modes; respective stability assessment is performed as well for each arrangement. In order to generalize the derived dynamics, it is shown that photovoltaic and wind generators may be represented by similar electrical equivalent circuits, possessing comparable small-signal dynamics. It is exposed that dynamic impedance of renewable energy generators is both operating point and environmental conditions dependent and hence plays a crucial role in the combined source-converter-load dynamics from affecting system damping to causing openloop instability in particular arrangements. Consequently, special care must be taken when designing power electronic interface intended to operate as a renewable energy generator power processor while at the same time the controller must be robust enough to ensure system stability for all expected environmental conditions. In addition, in case fixed closed-loop behavior is required through the whole operating range of the system, some kind of adaptive mechanism is required to estimate the dynamic impedance online. Several particular case examples of the proposed method presented in the literature are reviewed.

This paper presents a method for estimating the fixed and variable speed turbine performance index. The approach is based on Weibull wind probability distribution function and manufacturer-provided power curve. It is further shown that the existing turbine performance index formulation is only valid in case of variable speed turbines. A general approach to calculating the turbine performance index is derived, suitable for both fixed and variable speed wind turbines. Instead of choosing a particular model for approximating the power curve, commonly used polynomial fitting is employed. It is suggested to determine the best site for a given off-the-shelf turbine rather than finding the best theoretical turbine for a given site.

In this paper, the applicability of the well-known single-diode equivalent circuit to modeling amorphous silicon photovoltaic modules is questioned. It is shown that, unlike in mono- and polycrystalline modules, all of the equivalent circuit parameters are irradiation dependent. This dependence may be derived from either manufacturer-provided or measured I– V curves for different irradiation levels. In order to extract the equivalent circuit parameters, the suggested approach combines numerical solution of two transcendental and two regular algebraic equation systems with single-parameter fitting procedure. Two additional parameters are introduced to describe temperature dependence of photocurrent and diode reverse saturation current. As result, a set of seven parameters is obtained, comprehensively describing the panel performance for arbitrary ambient conditions. It is shown that characteristic curves obtained using the proposed approach match well the manufacturer-provided data for various values of temperature and irradiation.

The paper focuses on the quantitative analysis of Israeli Government’s targets of 10% renewable energy penetration by 2020 and determining the desired methodology (models) for assessing the effects on the electricity market, addressing the fact that Israel is an electricity island. The main objective is to determine the influence of achieving the Government’s goals for renewable energy penetration on the need for backup in the Israeli electricity system. This work presents the current situation of the Israeli electricity market and the study to be taken in order to assess the undesirable effects resulting from the intermittency of electricity generated by wind and solar power stations as well as presents some solutions to mitigating these phenomena. Future work will focus on a quantitative analysis of model runs and determine the amounts of backup required relative to the amount of installed capacity from renewable resources.

The paper offers a novel approach to parameter estimation of a single-diode solar cell/panel equivalent circuit, based on analysis of either technical characteristics supplied by the manufacturer or userobtained experimental I–V curve. The derived model allows predicting the solar cell/panel output for arbitrary environmental conditions. The method combines a solution of an algebraic equations system with an optimization algorithm. The main advantage of the proposed method is that in order to obtain the required parameters of the model, minimal set of experimental data is required. In order to validate the feasibility of the proposed approach, several solar panels of different types from several manufacturers were analyzed. The results demonstrate 0.1–0.5% estimation precision when the Standard Operation Conditions data from the manufacturers’ datasheets are employed.

Three approaches to calculating capacity factor of fixed speed wind turbines are reviewed and compared using a case study. The first “quasiexact” approach utilizes discrete wind raw data (in the histogram form) and manufacturer-provided turbine power curve (also in discrete form) to numerically calculate the capacity factor. On the other hand, the second “analytic” approach employs a continuous probability distribution function, fitted to the wind data as well as continuous turbine power curve, resulting from double polynomial fitting of manufacturer-provided power curve data. The latter approach, while being an approximation, can be solved analytically thus providing a valuable insight into aspects, affecting the capacity factor. Moreover, several other merits of wind turbine performance may be derived based on the analytical approach. The third “approximate” approach, valid in case of Rayleigh winds only, employs a nonlinear approximation of the capacity factor versus average wind speed curve, only requiring rated power and rotor diameter of the turbine. It is shown that the results obtained by employing the three approaches are very close, enforcing the validity of the analytically derived approximations, which may be used for wind turbine performance evaluation.

The manuscript presents a method of interfacing renewable energy generators by means of Maximum Power Line tracking rather than Maximum Power Point tracking. The maximum power line connects the maximum power points of output I–V curves of a source for different values of power producing parameter (wind, solar insolation etc.) and may be estimated offline with moderate accuracy. As a result, during the online operation, the maximum power point tracker only has to compensate for maximum power line inaccuracy and changes caused by slow temperature variations and system parameters drift. The approach allows reducing dramatically the bandwidth of the MPP tracking algorithms and simplifying the implementation, making analog MPP trackers a viable choice. The proposed method is shown to be a generalized version of the well-known loss-free resistor concept, referred to as loss-free load in the manuscript. Several particular case examples of the proposed method presented in the literature are reviewed.

In this paper, a method of designing an optimally arranged solar array for converterless matching to a known linear load is proposed and compared to the classical Maximum Power Point Tracking method. Long-time performance of both methods is examined for three common types of loads under real weather conditions. Test results indicate that only in case of a pure resistive load the Maximum Power Point Tracking-based solar system advantage is undisputed. In case of a load represented by a voltage source with internal resistance, the long term energy productions of the system employing a practical Maximum Power Point Tracking operated converter is on a par or lower than the converterless system energy yield.

The paper presents a simple approach to deriving IV curves of photovoltaic panels and small arrays for arbitrary environmental conditions on the basis of three points of a single operating curve data and short current temperature coefficient only. The proposed method does not employ fitting of any type and is solely based on a numerical solution of a system of transcendental equations. The equations are expressed in a dimensionless form, simplifying both the solution and photovoltaic panel parameters’ representation. The solution is used to find the values of normalized equivalent circuit elements for the available data and then perform an appropriate adjustment to obtain the operating curves for arbitrary conditions. The proposed method was applied to monocrystalline and polycrystalline commercial solar panels and was compared with both manufacturer-provided and experimentally measured operating curves to analyze the approach applicability and accuracy.

This letter presents a method for estimating the capacity factor of stall regulated wind turbines, based on the wind probability distribution function and manufacturer-provided power curve. It is further shown that the existing capacity factor formulations, e.g., for pitch regulated wind turbines, are a specific example of the derived method. Rather than using a particular model for approximating the power curve, polynomial fitting is employed in order to preserve the generality.

A method of rapid prototyping of a solar array simulator, based on low cost, off-the-shelf components is proposed in the paper. A commercial constant output voltage switching power supply is utilized as a power stage. It is shown that it is possible to gain control over output voltage of such a device by injecting variable analog voltage into the voltage feedback loop of the supply. As a result, by sensing the power supply output current and varying the injected voltage it is possible to change the output voltage according to a predefined relation and hence any static I-V curve may be emulated by the device. For simulating a solar array output characteristics, the desired I-V curve may be either digitized from a manufacturer provided datasheet, obtained experimentally or estimated from three basic current-voltage pairs (open circuit, short circuit, and maximum power points) using a dedicated algorithm. In order to demonstrate the proposed method, a prototype was designed and built based on available low-cost commercial components. Dynamic characteristics of the prototype were experimentally evaluated and three static I-V curves of a commercial solar panel were simulated. The resulting I-V output characteristics were shown to closely resemble datasheet I-V curves.

In the paper “An Analytical Solution for Tracking Photovoltaic Module MPP” by Farivar et al. (IEEE J. Photovolt., vol. 3, no. 3, pp. 1053–1061, Jul. 2013), a new method for approximating the maximum power point of a solar panel that is based on a single-diode equivalent circuit characteristic equation was proposed. The technique was shown to be computationally efficient and capable of retrieving the maximum power point in one step. The purpose of this note is complementing the method proposed by Farivar et al. by analytically demonstrating its validity.