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The current-fed isolated dc/dc converters are suitable solutions for applications requiring low high-frequency current ripple and convenient current control, such as fuel cells and Li-ion batteries. The existing current-fed isolated dc/dc converters are combined with a current-fed bridge-type terminal and a voltage-fed bridge-type terminal, which can only partially obtain the merits of the current-fed terminals. In this article, a dual-current-fed dual-active-bridge dc/dc converter is proposed with the inductor connection on both terminals. Hence, low high-frequency current ripple and convenient current control can be realized on both sides. Besides, it can also realize the voltage spike suppression without snubber circuits and has the inherent soft-switching operation and voltage boost function. Then, the operation principle, design process, and loss analysis of the proposed converter are presented in detail. The experimental results based on a proof-of-concept laboratory prototype are given to verify the steady-state and dynamic performance of the proposed converter. [ABSTRACT FROM AUTHOR]

A novel control technique that guarantees a ripple-free output current and voltage of a dc–dc multiphase staked interleaved converter is proposed. The conventional multiphase interleaved converters have been extensively used in various applications. However, ripple cancellation in these converters solely depends on the number of phases and can only be achieved at specific duty cycles. On the other hand, wide-range and ripple-free output are important paramount features for many modern applications. Therefore, the presented converter aims to combine the advantages of both the multiphase interleaved and the stacked converters into a single-unit converter suitable for high-power applications. Ripple-free output current/voltage is always guaranteed regardless of the number of phases and duty cycle values. This feature is accomplished by adding a fractionally-rated phase-leg to the conventional multiphase interleaved converter and modulating it with the proposed control approach. The configurable logic block, a state-of-the-art tool developed by Texas Instruments, is utilized to reduce the hardware size of the entire conversion system while increasing its speed and flexibility. Extensive simulation studies are carried out to confirm the functionality of the proposed control scheme. A laboratory porotype is developed to validate the effectiveness of the proposed control method experimentally. With only a few more components, significant reductions in output ripples are achieved. [ABSTRACT FROM AUTHOR]

Dickson-type dc–dc converters have gained renewed interest in recent years due to their best-in-class volt-amp switch utilization. In addition, “hybrid” switched-capacitor (HSC) structures increase passive component utilization while avoiding the slow-switching limit (SSL), and yet, most HSC work to date has done little to assess large signal voltage ripple behavior and subsequent passive utilization limits. This work contributes a comprehensive review of contemporary Dickson-type HSC converters before introducing eight fundamental reduced HSC Dickson structures, including three that are proposed here. Analysis allowing characterization of large signal operating points, capacitor sizing regimes, switching schemes, and maximum allowable power throughput is introduced. The analysis for “split-phase” switching is also presented in detail, without making small ripple approximations. Furthermore, an expression for large ripple flying capacitor energy density utilization is derived, assisting with optimal topology selection and revealing that split-phase operation may be preferable for conversion ratios greater than 6:1. All analysis is verified in simulation, with an additional discrete hardware prototype further validating a complex case of resonant split-phase timing. The analytical results of 17 distinct Dickson variations are recorded, assisting with topology selection and design. [ABSTRACT FROM AUTHOR]

The dual-active-bridge (DAB) is a typical topology of dc–dc converter for bus connection, voltage conversion, power transmission, and electrical isolation in dc power grids. The open-circuit switching fault (OCSF) may threaten the safe operation of DAB and should be eliminated in time. However, the researches on parasitic parameters mainly focus on traditional dc–dc converters, and there are still few discussions on parasitic parameters in the high-frequency dc–dc converter such as DAB. The power components are usually considered without parasitic parameters in OCSF analysis and tolerant control, leading to deviations in modality analysis and practical control for DAB. To solve this issue, the modality analysis considering parasitic parameters during OCSF in DAB is investigated, and the sneak circuits and electrical characteristics with parasitic parameters are discussed in this article. Besides, to realize fault tolerance for DAB during OCSF considering parasitic parameters, a new fault tolerance control strategy including modeling, topology transformation principle, and practical control architecture are also proposed. Compared with conventional fault tolerance strategy, the proposed strategy will be more efficient, rapid and feasible for DAB during OCSF process. The experimental results in DAB prototype verify correctness and effectiveness of analysis and proposed strategy. [ABSTRACT FROM AUTHOR]

The magnetic coupling of a practical wireless power transfer (WPT) system is greatly influenced by the variations in the alignment of the magnetic couplers. For a given coupling range, a WPT system is expected to output the required rated power with a given load. However, this requirement cannot be easily met by the widely adopted series–series or inductor–capacitor–capacitor compensation topologies in a conventional two-resonator WPT system. This article proposes a design methodology for three-resonator WPT systems to achieve a constant output power in a wide coupling range. The basic characteristics of the three-resonator WPT system are reviewed and the proposed design methodology is presented in detail. A 3.3-kW three-resonator WPT prototype is designed and built, achieving nearly constant output in the given misalignment range. The measured dc–dc efficiency of the prototype reaches 94.47 $\%$ at the rated power. [ABSTRACT FROM AUTHOR]

The three-phase dual active bridge (3ph-DAB) converter is a promising topology attracting increasing attention. However, because it is limited to symmetrical three-phase bridge control, the conventional single-phase-shift control method (SPS) remains the most common method for 3ph-DAB converter. The obvious shortcomings of SPS control include the soft-switching failure, massive circulating energy, and high root-mean-square (rms) current value at the light load, particularly with large voltage variation-ratio conditions. To overcome these drawbacks, this article proposes a novel asymmetrical phase shift (APS) control strategy. Unlike other optimized modulation schemes, this optimized strategy breaks the symmetrical control rules of three-phase bridges by introducing variable phase-shift angles among three-phase legs. The novel APS control strategy can substantially reduce the current's rms value and extend the soft-switching operation range due to these additional phase-shift angles. Further, the analytical solutions for the optimal phase-shift angles are derived by solving the global optimal condition equations. Analytical solutions, compared with complex numerical solutions derived by other optimized schemes, can be easily adopted in digital implementation and perform well under changing parameter conditions. Finally, experimental results verify the outstanding performance of the proposed modulation strategy. [ABSTRACT FROM AUTHOR]

Multisource switched-capacitor multilevel inverters are proper topologies when multiple dc sources are available as renewable energy sources. However, these multilevel inverters have the main drawbacks of requiring a large number of power semiconductors and capacitors and a low boost factor to achieve a large number of voltage levels, which complicate control, reduce performance, and raise the cost. This article presents two configurations for multisource switched-capacitor multilevel inverters. First, a basic multisource switched-capacitor topology is proposed with a small number of capacitors and semiconductors that produce a zero voltage level and a large number of positive voltage levels. The input dc sources are operated in an asymmetric trinary algorithm, while the capacitors are charged/discharged in a binary algorithm using parallel/series modes (without the need for any circuit balancing). Based on the proposed basic topology, two multilevel inverter topologies are proposed, which create bipolar output voltage levels using two different circuits at the output. The first proposed topology uses a standard H-bridge inverter at the output of the basic topology, while the second topology uses an extra switched-capacitor (self-balancing) circuit. The comparison indicates that both the proposed topologies have advantages over most of the reported multisource switched-capacitor multilevel inverters, such as a small number of capacitors, a small number of power semiconductors, low voltage stress, and high boost factor. Furthermore, the proposed topologies decrease the low cost factor in comparison to other topologies. The capacitors' capacitance, power losses, and voltage ripple losses are all measured and evaluated in detail. Theoretical research is validated with the use of laboratory prototypes to validate the performance of the proposed topologies. [ABSTRACT FROM AUTHOR]

A dual-modular-multilevel-converter (MMC) structure is presented that allows multifrequency power transfer between its ports. By exploiting a three-winding transformer, where the converter-side windings can multitask by accommodating currents with multiple frequency components, the proposed MMC structure can be deployed for two different applications: 1) a dc–ac MMC with independent control of currents in the two dc poles to accommodate unbalanced conditions in bipolar dc systems, and 2) a three-port MMC that can achieve simultaneous dc–dc and dc–ac conversions between an ac grid and two dc systems. DC flux cancellation is imposed in the transformer core by using a center-tapped connection of the converter-side windings. A unified control scheme is developed that independently controls dc and ac terminal power transfers while keeping submodule capacitor voltages balanced. Converter operation and dynamic controls are validated by simulation and experiment. [ABSTRACT FROM AUTHOR]

The star-connected Cascaded H-Bridge (CHB) converter is one of the most attractive multilevel topologies for medium/high-voltage STATCOM. However, due to the fact that CHB has separated dc-links, three-phase unbalanced active powers cannot exchange automatically, which, thus, requires extra zero sequence voltage (ZSV) to eliminate them. Especially when negative sequence current is compensated, the negative sequence current compensation range (NCCR) is seriously limited. To extend the NCCR, this article combines the CHB and the converter with a common dc-link, which is utilized to exchange and eliminate the unbalanced active power generated from CHB. Based on this new active power exchange way and conventional ZSV injection, a novel cluster voltage balancing control method is proposed to eliminate the unbalanced cluster active powers. Moreover, based on the proposed control, the NCCR is identified, which is larger than that based on the conventional control. Finally, the proposed control and the derived NCCR are verified by simulation and experimental results on a 400 V/7.5 kvar Hybrid Cascaded Converter STATCOM. [ABSTRACT FROM AUTHOR]

Modular multilevel converter (MMC) faces challenges ofcost and footprint in medium and high voltage grid applications. By adding a three-phase switching bridge on the basis of MMC, this article proposes a three-phase multiplexing arm modular multilevel converter (TPMA-MMC) with high power density and small volume. The multiplexing principle for TPMA-MMC is investigated, showing the multiplexing arm can be multiplexed for one-third fundamental period. After that, the subsection modulation scheme is further proposed for energy balance purpose. Compared with MMC, the number of submodules (SMs) and power devices are reduced by 22.8% and 13.83%, respectively, resulting in lower construction cost. Meanwhile, the SMs’ capacitance and the total capacitor energy storage of TPMA-MMC reduce greatly with the subsection modulation, which can greatly reduce the footprint and improve the power density. Moreover, the proposed TPMA-MMC outperforms the MMC in terms of efficiency. Finally, the topology and proposed modulation scheme are verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

In undersea long-distance dc power distribution networks, power converters are distributed over the length of the trunk cable carrying constant dc current. Under regular circumstances, these series-connected isolated dc–dc converters deliver power from the constant current feed to their respective loads while regulating their output voltage or current. However, in the event of a cable or other faults, the converters in the string lose power from the source, and hence bidirectional load(s) could be employed for continuing power delivery to the priority loads. In this article, it is shown how a dual active bridge (DAB) based LCL-T resonant converter can be designed to meet the requirements of driving such bidirectional loads to provide constant voltage to the load from a constant current source under regular operation and convert a voltage source to a constant current drive for the priority loads in the event of loss of power from the main feed. Steady-state modeling and analysis are furnished for the DAB LCL-T converter with three-angle modulation to derive all the dc and ac signals of the converter. Detailed design and modulation angle control are presented to minimize the overall VA rating of the resonant tank, transformer, and H-bridges. Experimental validation is provided for a prototype hardware system converting 1-A input current to 150-V output voltage in the forward direction and 1-A current drive from 150-V dc source in reverse power transfer, operating at 250-kHz switching frequency over a 50–500 W load range. [ABSTRACT FROM AUTHOR]

LLC resonant converter has been widely employed in electric vehicle (EV) charging applications. However, conventional frequency-modulated LLC converters generally demand a wide frequency variation range and are difficult to scale up, while the traditional phase-shifted (PS) LLC converters have the issues of ease of losing soft-switching condition and high turn-off current. In response to these challenges, this article proposes a new method for EV charging applications based on the capacitor-clamped LLC converter topology and fixed-frequency PS modulation. Compared with traditional PS LLC converters, the proposed method can achieve 1) smaller phase shift variation range, 2) lower turn-off current, and 3) wider soft switching range, resulting in higher efficiency. An 825-W prototype with 200 V input and 125–210 V output range verified the features of the proposed idea, and the efficiency reaches 97.82% at the maximum output power. [ABSTRACT FROM AUTHOR]

Modularity in hardware improves the manufacturability of power electronics systems and reduces maintenance costs. By paralleling modular ac–dc converters, the current capacity of SiC-based power conversion systems can be easily expanded. However, it is questionable which filter topology can be chosen for an arbitrary number of the converters ($N$). Considering interleaving, filters without any coupling may result in an overdesign. Meanwhile, filters that magnetically couple the paralleled converters may suffer from complexity in mechanical structure and $N-1$ redundancy. Based on these observations, this article proposes a filter structure that can be easily scaled to any number of converters. The proposed structure is comprised of a coupled inductor (CI) forming a loop of secondary windings, a single boost inductor on that loop, and a normally on normally closed (NONC) contactor per converter. Circulating currents are attenuated by the CI for any $N$. A single inductor rated for each channel realizes a boost inductor for a whole $N$ -converters, which can bring a significant benefit on power density and cost. When one of the converter faults, the faulty converter can be easily isolated from the system by the NONC contactor, thus achieving $N-1$ redundancy. The proposed filter topology is experimentally verified with a 20-kW full-SiC modular ac–dc converter. [ABSTRACT FROM AUTHOR]

Bidirectional capacitive power transfer technology makes it possible for energy sharing among multiple electronic devices. This article proposes an asymmetrical bidirectional power conversion topology to satisfy different input and output characteristics’ requirements and increase load variation tolerance. A π–T (CLC–LCL) resonant topology is designed for this bidirectional conversion mode with constant output voltage characteristics in both directions. A hybrid power flow regulation strategy is proposed by integrating multiple zero-voltage switching soft-switching operating points switching and phase-shifted mode. This method overcomes the problem of mixing two different type topologies (push–pull and full bridge) with two different power regulation modes (switch soft-switching operating points and phase shift), which provide a way to make two different chargers compatible. Simulation and experimental results verified the proposed method. [ABSTRACT FROM AUTHOR]

Based on the unipolar-duty-cycle (UDC) modulation technique, this article presents a hybrid control strategy for a series–series compensated inductive power transfer (IPT) system. By adjusting the duty cycle and the operating frequency, zero-voltage switching (ZVS) and constant-current output (CCO) can be achieved with varying coupling coefficients and load. Furthermore, as the proposed strategy enables the IPT system to lower the frequency of operation, it provides higher efficiency in the overall output power range than the conventional variable-frequency control methods. The basic principle of the UDC control strategy and its characteristics are introduced, and the system performance under UDC is analyzed and compared with the performance achieved by conventional control methods. Based on this, the UDC closed-loop control scheme, which combines PI control and hysteresis control, is proposed for the dynamic tracking of the ZVS and the CCO under a wide range of coupling coefficients and load. To validate the practicability of the proposed control strategy, a 500-W experimental prototype is configured. The simulation and experimental results indicate that the proposed scheme can stably and accurately track the ZVS and the CCO under varying parameter conditions, and it significantly improves the system efficiency. Especially, the system efficiency is improved by approximately 1.75% under light-load conditions as compared with that of the conventional control method. In addition, since the proposed method employs only one control loop, the cost and complexity of the IPT system are reduced. [ABSTRACT FROM AUTHOR]

The common inductor and common capacitor current sharing technologies with excellent current sharing capabilities and low cost have attracted a lot of attention in recent years. However, these methods have certain limitations when dealing with multiple resonate parameters mismatches of multiphase LLC converters. To solve this problem, this article proposes a unified common inductor and common capacitor scheme. First, the existing common inductor and common capacitor methods are reviewed. Based on the first harmonic approximation (FHA) analysis method, the limitations of these schemes are analyzed, and we find that the current sharing performance is not well when the multiresonant parameters are mismatched, which will cause the one-phase to bear more power, even overpowered and damaged. To realize a better current sharing of multiphase LLC modules, a unified common inductor and common capacitor method is proposed in this article, where the series resonant inductors and resonant capacitors in each LLC converter are connected in parallel. The current sharing performance of the proposed method is analyzed by the FHA analysis method, and the proof-of-concept prototype with a 480 W 24 V two-phase LLC converter was built to verify the effectiveness of the proposed method. Simulation and experimental results show that the current sharing error of the proposed method is 2.1% under half load and 0.9% under full load. [ABSTRACT FROM AUTHOR]

New emerging power inverter topologies are aiming at high-power density and efficiency with reliable performance. The recently proposed family of single-phase single-stage buck–boost inverters with output unfolding circuits have promising features for application in different fields. Nevertheless, the incapacity of injecting reactive power by the classical unfolding inverters has been assumed as its main drawback. Thus, our focus is on the reactive power injection capability of the single-stage buck–boost inverters with unfolding circuits. This attribute enables the converter to provide some extra ancillary services for friendly integration of the renewable energy resources and energy storage systems, providing support to the smart grid/microgrid, thus contributing to its power quality welfare. By means of a comprehensive analysis and implementation of proper closed-loop model predictive control, together with an adequate selection of the output capacitor, the single-inductor unfolding buck–boost inverter is capable of delivering reactive power to the utility grid. We used the simulation and experimental tests to validate the theoretical aspects. [ABSTRACT FROM AUTHOR]

In order to increase the power density and the lifespan of light-emitting diodes (LED) drivers, several studies have proposed active ripple compensation (ARC) techniques for minimizing the converter bulk capacitance. However, a common side effect of the ARC method is the increase in the total harmonic distortion (THD) of the converter input current. In this context, a frequency-based ARC technique is proposed as an alternative to the conventional ARC methodology, in which the duty cycle is modulated. The analyses presented in this article show that the frequency-based ARC approach applied to resonant converters has a better performance than the one used in hard-switching converters, since it allows for a huge capacitance reduction with a small THD increase. Furthermore, this article presents a generalized analysis of ARC techniques applied to integrated offline LED drivers, which reduce the number of components and the overall LED driver cost. The input current harmonic content and the output ripple reduction have been theoretically predicted for several converters. Experimental results gathered from a 96-W laboratory prototype supplied from a 127-V 60-Hz grid attested the superior performance of the frequency-based active ripple compensation, since a capacitance reduction of 66.6% has been obtained with an increase of only 0.9% in the THD. [ABSTRACT FROM AUTHOR]

This article proposes a multiport modular single-stage current-source solid-state transformer (SST) for applications like photovoltaic, energy storage integration, electric vehicle fast charging, data center, etc. The 7.2 kV 50 kVA current-source SST consists of five input-series output-parallel modules, each based on 3.3 kV SiC reverse-blocking mosfet-plus-diode modules. The proposed SST has some unique features. First, compared with the voltage-source or matrix converter-based SSTs, the current-source SST has a unique advantage of single-stage isolated ac/dc or ac/ac conversion with an inductive dc link, but no medium-voltage (MV) ac experiments have been reported. This article for the first time demonstrates MV ac current-source SST up to 7.5 kV peak. Second, the multiport SST has a buffer port for active power decoupling (APD) or energy storage integration. The double-line-frequency power ripple from single-phase ac grid normally results in a large capacitor size in MV SSTs. The APD scheme is proposed in MV applications for the first time to enable a reduced dc link and the electrolytic capacitor-less SST with high reliability. Third, for a direct grid-connected converter without line-frequency transformer, insulation and protection are critical. A medium-frequency transformer design passes 55 kV basic-insulation level (BIL) and 60 kV high potential dielectrics withstand test with only 0.09% leakage inductance. Importantly, a lightning protection scheme is presented to protect the SST itself from 90 kV BIL impulse. Fourth, the proposed current-source SST topology is a modular soft-switching solid-state transformer (M-S4T) with full-range zero-voltage switching and controlled dv/dt for low electromagnetic interference. These concepts are verified in a three-port M-S4T prototype with forced oil cooling under single-module, stacked-module, steady-state, and dynamic operations. [ABSTRACT FROM AUTHOR]

The double-sided inductor capacitor capacitor topology has been proposed in some national standards for wireless charging systems. However, misalignment between the transmitting and receiving coils usually leads to detuning and weak coupling, resulting in low output power and inefficiency. To improve power output under weak coupling, this article proposes a control method based on the variable inductor and capacitor (VLC). First, it is deduced that the zero phase angle input and full output power can be achieved by VLC regulation under certain misalignment. Second, the variable inductor using an EE-shaped core and pulsewidth modulation controlled capacitor are applied to achieve VLC regulation, and the principles and implementation of VLC are analyzed. Third, as the coupling coefficient k can be identified through the primary electrical parameters, a convenient and accurate coupling coefficient identification method is utilized to help VLC regulation. Finally, a prototype with a 3.3 kW output power and an 87.5% maximum system efficiency (dc–dc) is built to validate the proposed method. The experimental results are consistent with the theoretical analysis, proving that the output power is almost constant when k varies from 0.08 to 0.18. [ABSTRACT FROM AUTHOR]

The small satellite (SmallSat) industry has recorded incredible growth recently. Within this class, among mini-, micro-, and nanosatellites, the cube satellite (CubeSat) is primed for an explosion of growth. These satellites are fascinating for remote sensing, Earth observation, and scientific applications. Remarkable attention from the space operators makes it valuable because of its low cost, cubic shape, less manufacturing time, lightweight, and modular structure. Among the various subsystems comprising the SmallSat, the electrical power system (EPS) is the most crucial one because unreliable power supply to the rest is most of the time detrimental to the mission. The EPS is formed by electrical sources, storage units, and loads, all interconnected via different power converters, the operation of which must be closely orchestrated to accomplish efficient use of photovoltaic power, optimal battery management, and resilient power delivery. At the same time, the EPS design must address a series of challenges such as size restrictions, high power density, and harsh space environments (e.g., atomic oxygen, radiation, and extreme temperatures), which significantly impact the EPS electrical and electronic equipment. In terms of power systems, a SmallSat EPS can be considered a space microgrid owing to coordination and control of distributed generation, storage, and loads in a small-scale electrical network. From this point of view, this article reviews and explores SmallSat microgrid's research developments, energy transfer and architectures, converter topologies, latest technologies, main challenges, and some potential solutions, which will enable building a more robust, resilient, and efficient EPS. The research gaps and future developments are underlined before this article is concluded. [ABSTRACT FROM AUTHOR]

The single-switch topologies, e.g., the Class E topology, have the advantages of low component count, no shoot-through problem, simple driving circuit, which make it more suitable for high frequency low/medium-power wireless power transfer (WPT) applications. However, due to the high switch voltage stress, narrow soft switching range, bulky input choke, or ac inductor, its power delivery capability and applications are limited. In order to solve these problems, this article proposed a novel active clamp topology for high cost-performance medium-power WPT systems. The proposed topology offers low component count with no bulky inductor and low switch voltage stress, leading to high power-density, low cost, and compact size, i.e., high cost-performance for WPT applications. And the switch peak voltage can be adjusted and the soft switching operation can be achieved in a wide load range by designing the compensation capacitor and clamp capacitor. In this article, the detailed theoretical analysis and parameter design are discussed and the proposed topology is compared with the existing single-switch topology in terms of voltage stress, cost, and component count. A 120 W and 1 MHz active clamp WPT system is built and a 92.4% system efficiency is achieved with high cost-performance, which validate the feasibility of the proposed topology and the theoretical analysis. [ABSTRACT FROM AUTHOR]

A passive current sharing method for a two-phase common inductor LLC resonant converter is proposed in this article, and the relative mathematical analysis of current sharing error is carried out. The concept of a common inductor comes from the introduction of coupled impedance, where the resonant inductors of two phases are connected, which means that the separated two phases are coupled by an additional impedance. Obviously, there are four cases of coupled impedance, which are infinite impedance, infinitely small impedance, inductive impedance, and capacitive impedance, and they are all analyzed in the article. In addition, for different inductor and capacitor parameter differences, the two-phase common inductor LLC resonant converter has different current sharing characteristics, and there is an optimal solution for different coupled impedance for each difference. However, under each parameter difference, when the coupled index g is a negative number, there is generally a better current sharing effect. At last, simulation and experimental results have proved the correctness of the theoretical analysis. [ABSTRACT FROM AUTHOR]

This article proposes a single-ended hybrid resonant converter (SEHRC) for wireless charger to provide a cost-effective solution with high misalignment tolerance. A comprehensive characteristics analysis of the proposed converter is performed in both of time and frequency domain. The analysis discloses that the hybrid compensation performs impedance transformation which maintains the input impedance nearly constant. As a result, the optimum operation of SEHRC, including zero-voltage-switching, low voltage stress, high power transfer capability, and high efficiency can be maintained within a wide range of coupling coefficients. Also, it ensures a stable output current for both load and coupling variations. The design constraints and procedure are given. Furthermore, a zero-voltage-switching and zero-voltage-derivative-switching control scheme is proposed to achieve a higher efficiency and smaller output current fluctuation, as well as reduced peak switch voltage. Finally, a 1.3 kW prototype is built to verify the theoretical analysis. The test results demonstrate that the peak voltage of the proposed SEHRC is less than 2.7 times the input voltage. When the coupling coefficient varies 2.7 times, the output current changes by 1.16 times. [ABSTRACT FROM AUTHOR]

The proposedisolated buck–boost series resonant dc–dc converter contains two full-bridge hybrid switching cells capable of half-bridge operation. This feature is regarded as topology morphing control. Voltage buck regulation requires special modulations applied to the primary-side hybrid switching cell. In contrast, voltage boost regulation requires special modulations for the secondary-side hybrid switching cell. Combining the topology morphing control with the buck–boost regulation capability, a novel dc–dc converter operating in six different modes was derived. Moreover, the converter is capable of bidirectional operation. This article describes the influence of the topology morphing control on the dc voltage gain of the converter, which results in three boost and three buck modes. The six modes are described, and equations for the converter's dc voltage gain are provided. Based on the selected design guidelines for the power part and the control system, a 350-W prototype was designed and built. Experimental results confirm the theoretical expressions for the converter's dc voltage gain. Experimental efficiency is provided in a wide input voltage range for both energy transfer directions. Operating points with the highest thermal stress of components are analyzed with corresponding power loss breakdown calculations, confirming the measured thermal results. [ABSTRACT FROM AUTHOR]

Transformerless inverters, most of which are H-bridge inverters, have been widely used and studied in grid-connected power systems in the last decades. However, the H-bridge inverter is affected by the low- and high-frequency common-mode voltage between the input and output terminals, resulting in a large common-mode leakage current. An alternative solution is to connect the ground of the input terminal to the output load or grid, that is, the dual-grounded inverter. In this case, the low- and high-frequency common-mode voltages can be mitigated or eliminated. As a matter of fact, scholars have made several research results on dual-grounded inverters. However, as of now, there is still no literature that comprehensively and systematically summarizes these research results. To fill this gap, this article classifies different types of dual-grounded inverters from the perspective of topology for the first time, and compares and summarizes their advantages and disadvantages. More than 60 works of literature have been reviewed to identify the practical implementation challenges and research opportunities in the application of dual-grounded inverters. [ABSTRACT FROM AUTHOR]

Inductive power transfer (IPT) has been widely applied in various applications such as electric vehicles and consumer electronics. In this article, a voltage controller base on an improved pulse density modulator (IPDM) for H-bridge active rectifier in IPT is proposed. To reduce the power loss caused by the pulse sequence of the traditional pulse density modulation (PDM) controller, a general optimization method of the pulse sequence is given and proved in detail. More importantly, an analytical model, which illustrates the relation between interharmonics and power losses of the system, has been derived. Compared with traditional PDM, the stress on switching devices is reduced under various load resistance, and the overall system efficiency can be improved. The experiment results based on a 1-kW laboratory prototype demonstrate the proposed IPDM design method. Under different load conditions, ranging from 22.6–102 Ω, the overall system efficiency could reach up to 96%. Compared with phase-shift modulation and PDM, the efficiency is at most improved by 3.508%. [ABSTRACT FROM AUTHOR]

In the last thirty years, the integrated gate-commutated thyristor (IGCT) has been employed in medium voltage $\,\mathrm{M}\mathrm{W}$ power level converters and has demonstrated some of the lowest conduction losses of any actively controlled device in traditional hard-switched, sub- $\,\mathrm{k}\mathrm{Hz}$ applications. Extending the use of the device to medium frequency applications, such as dc transformers is possible through soft-switched operation, where low turn-off current and zero-voltage turn-on significantly reduce switching losses. For this purpose, this article explores the tradeoffs in the transition between zero-voltage and zero-current switching conditions of reverse conducting IGCTs. Switching conditions resulting in minimal switching loss are identified for standard commercial devices and engineering samples subjected to increased electron irradiation to reduce switching energy at the expense of on-state voltage. The operation of the IGCTs at the record frequency of 5 $\mathrm{k}$ $\mathrm{Hz}$ is thermally validated under load in the identified switching conditions. [ABSTRACT FROM AUTHOR]

This article proposed a self-adapted model predictive current control (SA-MPCC) method to reduce the switching loss of the five-phase open-end winding permanent-magnet synchronous motor (OW-PMSM). The proposed SA-MPCC method regards the OW-PMSM drive system as two separate parts by utilizing the flexibility of the OW-PMSM system, thus generating and applying the phase voltage to armature winding independently. The virtual voltage vectors and multivector duty cycle modulation strategy is adopted to maintain a good steady-state and dynamic behavior. Then, the self-adapted decision is generated to choose one inverter work solely, or two inverters work cooperatively. When one inverter is used, another inverter is closed. The first inverter is clamped to optimal virtual voltage vectors when two inverters work together. The clamping to virtual voltage vectors or zero vectors can reduce the switching loss in both sides of the dual inverter. Finally, the experimental results verify the effectiveness of the proposed SA-MPCC method. [ABSTRACT FROM AUTHOR]

This article addresses the design of reconfigurable single-inductor multiport converters with bidirectional power flow, no cross regulation, and simple control. The design uses both the voltage-source-mode and current-source-mode cells, thus allowing a full range of connectivity. The proposed single-inductor converters offer high modularity and scalability while offering bidirectional power flow and no cross regulation. The single-inductor structure reduces the overall size. The adoption of voltage-source-mode and current-source-mode cells leads to high modularity. High scalability is achieved due to arbitrary ports being allowed to the derived converters. Moreover, the topology inherently achieves no cross regulation among the output ports. The ports of the derived converters are reconfigurable, permitting transformation among single-input multi-output mode, multi-input multi-output mode, and multi-input single-output mode. Through the transformation of operating modes, bidirectional power flow is achieved. Thus, regenerative loads can be integrated seamlessly. In terms of control, the absence of cross regulation permits the adoption of very simple control design, leading to high flexibility. Thus, the derived converters can integrate multiple and various kinds of terminating sources and loads simultaneously with simple control methods. A reconfigurable single-inductor four-port converter is presented for illustration. Finally, experimental results are presented to verify the analytical findings. [ABSTRACT FROM AUTHOR]

This article puts forward a hybrid model predictive control (H-MPC) for an inner-interleaved hybrid multilevel converter (IHMC). The sign patterns of the original and shifted reference vectors in the original and virtual space vector diagrams (VSVDs) are used, respectively, to realize the phase-disposition pulsewidth modulation (PWM) and determine the low-frequency switching states. Then, the three adjacent vectors are selected in the second-layer VSVD and the optimal current tracking is safeguarded by the duty cycle optimization of the three adjacent vectors. Finally, through applying the phase-shifted PWM to the two interleaved legs, a constant and doubled equivalent switching frequency can be achieved, which further paves the way for dc-link and floating capacitor voltages balancing and circulating current mitigation with the use of the straightforward duty cycle adjustments. The proposed H-MPC enables the decoupling of the low- and high-frequency stages in the IHMC and also reduces both output current ripples and computational burden while achieving a constant switching frequency simultaneously. Comprehensive simulation and experimental studies on an all silicon carbide prototype verify the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

Unbalanced dc-link voltages occur when five-level flying capacitor (5L-FC) rectifier has dual dc loads of different rated voltages. Compared with traditional continuous pulsewidth modulation (CPWM) strategies, discontinuous PWM (DPWM) methods have more advantages in high-frequency and high-power applications for less commutation and higher efficiency. Therefore, this article proposes a carrier-based DPWM method for 5L-FC rectifiers with unbalanced dc-link voltages. The proposed method is first analyzed in the revised space vector diagram considering unbalanced dc voltages to divide subsectors and find available clamping modes, then it is implemented by applying carrier-based PWM with injecting clamping compensation component, which greatly reduces the implementation complexity. There is a pair of redundant clamping modes with opposite effects on the neutral-point (NP) in each subsector. Thus, the NP voltage can be actively controlled by selecting suitable clamping mode in each subsector. In addition, the allowable ranges of unbalanced voltage degree and unbalanced power degree are investigated in detail. Simulations and experiments verified the effectiveness and performance of the proposed method. [ABSTRACT FROM AUTHOR]

This article presents a self-configurable and self-poweredactive rectifier that operates from 0.25–20 V for energy harvesting applications. The proposed circuit self-startups from a low voltage using a charge pump and amplifies the voltage with a voltage doubler topology to provide succeeding circuits such as boost converters with a higher voltage. When the voltage of the energy harvester reaches a high threshold, the circuit switches its topology to a full-wave rectifier that does not amplify the voltage. The start-up circuit can limit its voltage intake to prevent boosting the high voltage, which may damage the whole circuit. Comparators with a maximum operating voltage of 5.5 V used in the implementation of the rectifier are protected by a diode and resistor based circuit. A piezoelectric energy harvester (PEH) that has a wide open-circuit voltage of 0.4–15 V under the acceleration of 0.04–0.3 g was used to test the circuit. The experiment results showed the rectifier can startup from 0.25 V and switch its topology according to the PEH voltage. The voltage and power conversion efficiencies are over 90% in most cases. [ABSTRACT FROM AUTHOR]

Variable speed drives (VSDs) for electric motors are a foundational component of global electrification, with electric motors consuming 45% of global electricity. Conventional three-phase buck–boost inverter topologies have substantial low-frequency current stresses in the buck–boost inductor, driving size, losses, and cost in VSD systems. In this letter, we propose a novel circuit topology for phase-modular three-phase buck–boost inverter systems based on the four-switch noninverting buck–boost concept, which we call the return path inductor Y-inverter (RPI-YI). By relocating the buck–boost inductors from the forward current path to the return path, the RPI-YI concept reduces the inductor rms and peak current stresses by up to $90 \%$ compared to a conventional topology, resulting in a potential magnetics volume reduction of $80 \%$. The RPI-YI concept, therefore, supports more compact, efficient realizations of modular buck–boost VSD systems. [ABSTRACT FROM AUTHOR]

Multilevel inverter are popular solutions in photovoltaic power station, wind farm, and other renewable energy generation. This article presents a three-phase five-level inverter with high dc voltage utilization. A significant feature of the inverter is that its maximum dc voltage utilization is twice that of the traditional three-phase inverters such as neutral point clamped, flying capacitor (FC), cascaded H-bridge, and active NPC. What is more, the inverter can realize the self-starting and self-balancing of the FC, and the self-balancing of the dc-link capacitors, so the complex FC voltage balancing strategy and bus midpoint voltage control method are not needed anymore. The voltage and current stresses analysis and the design guidelines of components are discussed in detail. A comparison with some existing topologies has also been made to highlight its performance. Taking one phase as an example, both the simulations and experiments are carried out to verify the validity of the proposed inverter and modulation strategy. [ABSTRACT FROM AUTHOR]

This article is devoted to developing a unique series-winding drive (SWD) topology, analyzing and implementing its control schemes for asymmetrical multiphase permanent magnet synchronous motor (PMSM). Proposed SWDs have higher voltage utilization than ordinary wye or delta connection, but vary with the number of inverter legs and connection sequence. Also, they have a simpler topology, fewer inverter legs, and power modules than the open-end winding drives. The article selects the typical asymmetrical six-phase (ASP) PMSM as the target. The complex space vector mapping is screened and simplified by unified hexadecimal coding for both eight-leg and seven-leg drives. Given the multiple suspaces in ASP-PMSM, a multistage decoupling space vector modulation scheme is proposed and improved for SWDs. It incorporates the processes of vector synthetization, cost function minimization, and zero-sequence compensation. Prototype fabrication and control experiments are carried out. Results show that the proposed MSD SVM is applicable to all connection sequences. It can suppress the harmonic current to a quite low level, in both steady-state and dynamic states. Also, this article discusses the current burden of the inverter and provides suggestions. [ABSTRACT FROM AUTHOR]

A charging strategy that transitions from constant current (CC) mode to constant voltage (CV) mode is typical for lithium batteries. This presents design challenges for inductive power transfer (IPT) chargers to achieve high efficiency. In this article, a multiband frequency tracking control is proposed to match CC and CV modes and to mitigate misalignment. As in prior work, two load-independent frequencies fCC and fCV are used for respective CC and CV outputs. Unity power factor can be achieved when fully aligned. For misalignment cases, two narrow frequency bands around fCC are selected for control to deliver target output currents and limit reactive power. The duty ratio of the inverter is controlled to set target output voltages. A single-stage IPT system with a series LCC topology is analyzed. The proposed control has advantages of narrow operating frequency ranges, high misalignment tolerance, direct design procedures, and high efficiency in both CC and CV modes. The method is verified on a 4.4 kW prototype with a 150 mm air gap. Experimental results show that the target CC and CV charging profile can be achieved with up to 120 mm of lateral misalignment. When fully aligned, the maximum system conversion efficiency reaches 97.5%. It stays above 95.5% and 93.3% over the entire CC and CV mode ranges. [ABSTRACT FROM AUTHOR]

Hybrid and resonant switched-capacitor (SC) convertersenable efficient utilization of both active and passive components, and have the potential to achieve higher efficiency and higher power density than conventional SC and magnetic-based converters. One or more added inductors offer an additional degree of freedom in the design space. It is of great interest to understand the tradeoffsbetween capacitor and inductor size and volume allocation. In this article, we analyze the reactive energy processed by the passive components and use it to calculate the total passive component volume. It is shown that the total passive component volume of resonant SC (ReSC) converters can be expressed as a function of flying capacitor voltage ripple, and the optimized capacitor voltage ripple that minimizes the total volume is dependent on topology specific parameters and the relative energy density ratio between capacitors and inductors. Moreover, we also demonstrate through theoretical analysis and experimentation that ReSC converters use significantly less passive component volume than conventional SC and buck converters for the same amount of power converted. Next, to compare different ReSC topologies, a normalized passive volume parameter is proposed for simple and fair comparison. This can be used along with a normalized switch stress parameter (based on switch VA ratings) to create a framework to showcase the relative performance of different topologies. This framework can be used to visualize and compare the passive and active component utilization among different topologies. Additionally, the proposed reactive power analysis is extended to hybrid converters with regulation capability. [ABSTRACT FROM AUTHOR]

Active magnetic bearing (AMB) technology has been widely used in high-speed electrical machines. Power electronics controller amplifier is an important segment in AMB system. Failure of power electronics device is a common threat to the reliability of AMB amplifier and can cause serious damage. In order to improve the robustness of the amplifier, this article proposes open-circuit fault-tolerant control strategies based on different topologies. For single-axis systems, a pair of windings with a single degree of freedom can work in four different working modes based on the three-phase full-bridge structure. It can detect and locate the open-circuit fault of a power electronics switch in operation. After promotion to multiaxis systems, a novel kind of topology for amplifier with fault tolerant strategy has been proposed that can also detect the open-circuit fault of power electronics switch and switch to fault tolerance mode for a multiaxis system. Fault tolerant experiments verify the feasibility and rapid response of different fault tolerance strategies with an AMB testbed in this article. [ABSTRACT FROM AUTHOR]

Recent developments of fast-charging power delivery protocols are driving ac–dc adapters to 100-W power ranges. Conventional solutions in this power range employing a two-stage topology and a big twice-line frequency buffer capacitor are generally costly and bulky. This article presents a patent-pending modulation method for an active-clamp flyback converter, allowing for a single-stage adapter design with reduced capacitance requirements and higher efficiency. This is achieved by exploiting the inherent energy storage capability of the clamping capacitor while turning it into an active power buffer. No hardware modifications are needed, while all salient features of active-clamp flyback converter, i.e., soft switching and leakage recycling, are retained. Operating principles and detailed controller design are discussed, and a 100-W laboratory prototype is built. The prototype achieves 94% peak efficiency and up to 92% size reduction of the buffer capacitor. The experimental evaluation shows that the new single-stage solution enabled by the proposed modulation method is superior to the conventional two-stage and single-stage solutions in terms of cost, conversion efficiency, and power density. [ABSTRACT FROM AUTHOR]

Given the telecom base transceiver station (BTS) load mission profiles, a mixed conduction mode (MCM) control for a bridgeless boost PFC converter (IPOS boost) is proposed to mainly improve its power factor and reduce the input current total harmonic distortion (THD ${_{\mathit{i}}}$) in the light-load conditions. The principle of the MCM control and the efficiency analysis are introduced. Then, the experimental verification is performed to show the control effectiveness and performance improvements. Furthermore, a mission profile-based reliability assessment for the PFC converter is presented to analyze the IPOS boost under the classical average current (AVC) control and the proposed MCM control, along with its conventional boost counterpart under the AVC control. Considering the measured efficiency data and BTS typical mission profiles in a rural area, the analysis results indicate that given 20 years of operation, the accumulated failure of the IPOS boost under the AVC controls is 0.27%, and is further decreased to 0.24% by just the software update with the proposed MCM control. By contrast, the accumulated failure of the conventional boost counterpart under the AVC control is 2.06%, much higher than the IPOS boost. [ABSTRACT FROM AUTHOR]

This article proposes an optimized design for a wireless power transfer converter serving as an auxiliary power supply in a medium-voltage, high $\mathrm{d}v/\mathrm{d}t$ modular conversion system. A CLLC-CL circuit topology is implemented to generate a load-independent output voltage with a coupling-coefficient-independent resonant frequency. The output voltage of the circuit can be tuned by changing one pair of resonant LC parameters, which decouples the circuit gain from the coil design. Essential parameters of coil and magnet are extracted analytically or numerically to avoid time-consuming 3-D finite element analysis simulations for the subsequent optimization. After the design of the circuit and coil, a multiobjective optimization is carried out with objectives being efficiency, isolation capacitance, and insulation rating of the converter. Finally, experiments demonstrate a 48- to 48-V dc–dc converter with 100 W output power, 92.78% efficiency, 2.78 pF isolation capacitance, and 27 kV insulation rating to validate the optimization result. [ABSTRACT FROM AUTHOR]

A novel three-port cascaded multilevel solid-state transformer (CM-SST) is proposed in this article, which is based on modular multilevel converter submodules (SM) interconnected by high-frequency link (HFL), forming a decoupling channel to SMs and a low-voltage dc port. The common high-frequency bus in HFL helps to reduce the numbers of secondary full bridges in the form of multiplexing. The decoupling channel achieves the automatic balancing of capacitors voltage and natural elimination of SM ripple power, so the arms second-order circulating current can be eliminated from the root cause. Therefore, the CM-SST can simultaneously realize the switches decreasing, capacitance size reducing, arms circulating current elimination, and control simplification. In this article, the topology, equivalent model, HFL design, ripple-power decoupling, power loss, and control scheme are analyzed in detail. In addition, an evaluation of CM-SST compared with the traditional methods is provided, including sizing, components count, control, and efficiency. Finally, the correctness and effectiveness of the proposed scheme are verified by the simulation and experiment. [ABSTRACT FROM AUTHOR]

In wireless power transfer (WPT) system, the information of mutual inductance and load resistance is usually needed for the front-end to regulate power and efficiency. To acquire the values of these two parameters without wireless communication system and without affecting the output power, this article proposes an identification method based on the pulse density modulation (PDM) technique. The underlying principle is to obtain a range of interharmonics by altering the sequence of PDM. First, the PDM strategy brings in interharmonics, which can be identified through fast Fourier transmission (FFT). Then, these interharmonics are used to established multiple sets of equation related to front-end impedance and the two unknowns. Finally, with the least-square approximation, mutual inductance and load resistance can be estimated. This article notices that the sequence of PDM strategy could affect the amplitudes of interharmonics, and selects the sequences to maximize the magnitudes for less sensitivity to measurement errors. Experimental results show that the relative errors of identification are less than 5% when the nominal values of capacitors are the same as actual values, and reach 7.40% when considering the nominal values may deviate from the actual values. Besides, the output power and efficiency are not affected during the identification process. This proposal requires only magnitudes of voltage and current in the transmitter side, no other hardware is needed, and works with the fixed frequency, which is suitable for any frequency range. [ABSTRACT FROM AUTHOR]

The open-circuit (OC) faults for T-type three-level inverters often share similar distorted output features, which are usually distinguished by adopting invasive methods. The purpose of this article is to locate the OC fault by rebuilding the established phase voltage model according to the hypothesis method. Based on the vector decomposition principle and voltage-second balancing theory, the output phase voltage model is established considering neutral point voltage unbalance and time-offset injection. The hypothetical phase voltage vector and residual for fault reasoning can be obtained by inputting the suspected OC faults positions to the model. The hierarchical fault diagnosis scheme involves two steps. First, the group-level fault can be located according to voltage residual vector amplitude and angle. Considering the impact of parameter error, dead time, and delay time, an adaptive residual vector amplitude threshold is designed. Next, the device-level fault can be located by building two suspected phase voltage models to approximate the real system. Furthermore, the fault location rules under zero-crossing (ZC) and non-ZC conditions are summarized. Especially, the proposed hypothesis method has correctness verification ability to avoid misdiagnosis. Experimental results show the robustness and effectiveness of the proposed low coupling fault diagnosis method. [ABSTRACT FROM AUTHOR]

Since LLC converter is capable of naturally creating the soft-switching condition to improve the overall efficiency, it is widely used in dc–dc applications. Using LLC resonant tank to realize soft switching for three-phase ac–dc converters would be a very promising solution to high efficiency and low cost ac–dc conversion, an LLC-based three-phase single-stage ac–dc converter was configured by taking advantage of three-phase voltage feature $ u_{\mathrm a}$ + $ u_{\mathrm b}$ + $ u_{\mathrm c}$ = 0 and incorporating three bidirectional switches. Because of time-varying feature of three-phase voltages, the input voltage of the converter to the LLC resonant tank is no longer a symmetrical square wave, but a time-varying and asymmetrical three-level waveform, which makes the analysis of the resonant circuit behavior much complicated. Some traditional analysis methods, such as fundamental harmonic approximation and its variants, are impossible to deal with. To overcome this analysis obstacle, this article proposes a numerical analysis method to analyze the time-varying three-level LLC resonant tank for this converter. According to the monotonous change of LLC input voltage in one fundamental cycle, it calculates and determines the time durations of three phases and the corresponding operation modes in each switching cycle. And this numerical analysis method is used to calculate the numerical relationship between the two control variables (switching frequency $ f_{\mathrm s}$ and duty cycle $ D_{\mathrm M}$) of this converter and the voltage gain and power level, which is a guideline for the design of the resonant tank parameters and control strategy of the LLC-based three-phase single-stage ac–dc converter. Finally, the time-varying waveforms of $ f_{\mathrm s}$ and $ D_{\mathrm M}$ obtained by numerical calculation well match the PSIM simulation results, and a 3.3-kW three-phase 220Vac input and 48Vdc output prototype was built to verify the effectiveness of the proposed numerical analysis method and the feasibility of the control strategy. [ABSTRACT FROM AUTHOR]

In this article, a novel electric-drive-reconstructed onboard charger (EDROC) is proposed for the solar-powered electric vehicle that incorporates a six-phase machine drive. The power traction inverter and the machine are re-leveraged to implement charging operation, further minimizing the incremental mass accordingly. In particular, charging and driving operations can be simultaneously carried out via the vehicle-roof photovoltaic panels, significantly expanding EV mileage range. First, the operation scenario and the topology of the proposed EDROC are introduced. Next, the operational principle is analyzed, as well as the indispensable conditions for safe and stable operation are studied. Thereafter, control schemes are designed and elaborated in terms of the simultaneous driving and charging mode and the dc charging mode. To this end, a 2-kW laboratory prototype is conducted, and experimental results are presented to verify the steady-state and dynamic behavior of the proposed EDROC system under different operation modes. [ABSTRACT FROM AUTHOR]