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This paper presents bidirectional grid-connected modular multilevel converters (MMC) with direct digital control and division-summation processes to achieve power-injection and rectification functions. A direct digital control is developed to track current references, regulate dc-bus voltage and cell voltage, and balance the upper and lower dc-bus voltages. It can accommodate wide filter-inductance variation and take care of source voltage harmonics to achieve tight current tracking and low distortion output current. Based on the power-balance principle, the commands of arm currents can be determined directly. In this paper, the MMC configuration is introduced first, and then the control laws for current tracking and voltage regulation are derived in detail. Experimental and simulated results obtained from two 50 kW MMCs operated in power-injection and rectification modes have verified the analysis and discussion. [ABSTRACT FROM AUTHOR]

This paper presents an interleaved boost converter with a bifold Dickson voltage multiplier suitable for interfacing low-voltage renewable energy sources to high-voltage distribution buses and other applications that require a high-voltage-gain conversion ratio. The proposed converter was constructed from two stages: an interleaved boost stage, which contains two inductors operated by two low-side active switches, and a voltage multiplier cell (VMC) stage, which mainly consists of diodes and capacitors to increase the overall voltage gain. The proposed converter offers a high-voltage-gain ratio with low voltage stress on the semiconductor switches as well as the passive components. This allows the selection of efficient and compact components. Moreover, the required inductance that ensures operation in the continuous conduction mode (CCM) is lower than the one in the conventional interleaved boost converter. The distinction of the proposed converter is that the inductors’ currents are equal, regardless of the number of VMCs. Equal sharing of interleaved boost-stage currents reduces the conduction loss in the active switches as well as the inductors and thus improves the overall efficiency, as the conduction power loss is a quadratic function. In this paper, the theory of operation and steady-state analysis of the proposed converter are illustrated and verified by simulation results. A $\text{200-W}$ hardware prototype was implemented to convert a $\text{20-V}$ input source to a $\text{400-V}$ dc load and validate both the theory and the simulation. [ABSTRACT FROM AUTHOR]

This paper proposes a new class of topologies of single-stage high-frequency ac-link power converters, which is capable of providing both voltage step up/down within a wide frequency and voltage ranges. The proposed family, which supports bidirectional power flow, can interface various single/multi-port dc and/or single/multi-phase ac systems to provide dc–dc, dc–ac, ac–dc, or ac–ac power conversion. In this family of converter, which offers a very modular structure, a small inductor that forms the link exchanges power entirely or partially between the source and load. The proposed family can function in buck, boost, and/or buck–boost modes of operation, and a combination of these modes of operation is also feasible. In comparison to the parallel inductive four-quadrant link converters, the proposed family features a significantly reduced link peak current, reduced switch ratings, and reduced total number of power switches. These features enhance the efficiency, reduce the total cost, and increase the power density of the system. In order to further improve the overall efficiency of the system, minimize the current/voltage stress over all utilized semiconductor devices, and lower electromagnetic interference (EMI), a small capacitor is placed in parallel with the link inductor to realize soft-switching operation for the proposed configurations. Moreover, the proposed converters have the potential to incorporate a lightweight single-phase high-frequency transformer for electrical isolation. The proposed circuit topologies prevent reverse recovery issues and eliminate losses corresponding to body diodes of power switching devices via utilizing power switches in conjunction with external fast recovery diodes. The proposed family offers a very high level of reliability owing to its immunity from short circuit of input and output terminals and open circuit of the link inductor, which may occur in other power converters due to commutation problem resulting from a short deadtime or an overlap time between switches, unwanted control command, delay in electronic circuits, or EMI noise's misgating on or off, in addition to the absence of electrolytic capacitors in the power circuit. A control approach is also developed to regulate input and output currents in one stage of power conversion. A detailed theoretical analysis, operation, design methodology, and control strategy of the proposed family are provided in this paper, and the effectiveness and performance of the proposed converter family are verified via simulation results and experimentally. [ABSTRACT FROM AUTHOR]

In this paper, a novel high-conversion-ratio isolated bidirectional dc–dc converter for distributed energy storage systems is proposed. In the buck mode, the proposed converter is equivalent to that of a cascade consisting of an isolated buck–boost converter and a buck converter, thus achieving a high step-down ratio. Likewise, in the boost mode, the converter is equivalent to the cascaded structure consisting of a boost converter and an isolated buck–boost converter, and then, a high step-up ratio is achieved. Therefore, the proposed topology exhibits a high conversion ratio with low transformer turns ratio, improving the efficiency of high-frequency transformers and the integration and reliability of the control system. In addition, voltage spikes caused by the leakage inductance can be avoided as the leakage inductance energy is released to capacitors in a high-voltage side or a low-voltage side. Moreover, a zero-voltage-switching (ZVS) operation reduces switching losses and improves the conversion efficiency. The operating principles and theoretical derivations of the proposed converter along with ZVS implementations are discussed in detail in this paper. Furthermore, the validity and performance of the proposed converter are verified using a prototype with 600-V high voltage, 48-V low voltage, and 2-kW output power. [ABSTRACT FROM AUTHOR]

In this paper, a new class of bidirectional partial-resonance power converters is presented. The proposed family can be configured to interface single- or multi-port dc, single- or multi-phase ac systems at input-side and/or output-side. The proposed family offers a very modular structure, which can lead to cost reduction from a common designed module. In this converter, which accomplishes power conversion in a single stage, a small inductor placed in series with the input and output switch-bridges forms the link. This small link inductor is responsible for transferring power between different ports of the system. The proposed topologies can operate in buck, boost, and buck–boost modes of operation to step up and/or step down the voltage. In buck–boost mode of operation, the converter is controlled such that the power is entirely transferred through the link inductor; whereas, in buck or boost modes of operation only a fraction of the power is transferred through the link inductor, and the remaining power is directly transferred from input phases to the output phases. Galvanic isolation, which is typically a prominent factor contributing to power density of a converter, can be provided by means of a compact and lightweight single-phase high-frequency transformer added to the link. In comparison with earlier generations of partial-resonance inductive-link power converters, in the proposed converter, the level of link peak current and consequently power-loss, as well as voltage and current stress of switches are dramatically decreased. A very small film capacitor can be placed in parallel with the link inductor to facilitate zero-voltage-switching (ZVS) operation for all the switches/diodes. Apart from increasing the overall efficiency, minimized dv/dt stress and improvement in power density are achieved by adding the link capacitor. The proposed converter employs four-quadrant switches, i.e., bidirectional-conducting bidirectional-blocking switches, and charges the link inductor in both positive and negative directions in each cycle. In view of this, better utilization of the link inductor and lower total harmonic distortion (THD) are offered. Furthermore, two distinct switching algorithms are developed for the proposed family of converters. In this paper, the detailed behavior of the proposed family is investigated analytically, and simulation and experimental results are presented to evaluate the performance and effectiveness of the proposed converter. A low-power proof-of-concept prototype with input voltage of 59 V/161 V, load voltage of 178 V/73.5 V, maximum switching frequency of 4.9 kHz/3.65 kHz at 215 W/450 W in a step-up/step-down operation is considered for the experimental verification. [ABSTRACT FROM AUTHOR]

This paper proposes a high-power-density and reliable inverter topology, which transfers the maximum power of a PV array to the load in one power conversion stage. The single-stage power conversion, along with the soft-switching capability of the proposed three-phase PV inverter promises high efficiency at all operating points. Instead of a capacitive dc link that decouples the dc–dc converter and the voltage source inverter in traditional two-stage PV inverters, a high-frequency capacitive ac link is employed in the proposed inverter, which enables exploiting a very small film capacitor, rather than a bulky electrolytic capacitor, for transferring power. Eliminating electrolytic capacitors prolongs the lifetime of this inverter. Considering the long lifetime of PV modules, this feature is of high importance in PV applications. The high-frequency ac link also allows using high-frequency transformers for providing galvanic isolation. Therefore, this inverter is expected to have a very high power density. This paper presents principles of the operation and control, design, and analysis of this inverter, and verifies the performance of the inverter through two prototypes: a 2-kW Si-based prototype and a 2-kW SiC-based prototype operating at different switching frequencies. [ABSTRACT FROM AUTHOR]

A single-stage three-phase ac–ac converter benefiting from a high-frequency alternating link voltage is proposed in this paper. In this converter, a very small film capacitor can transfer the energy from the input to the output, owing to the high-frequency alternating voltage of the link. This eliminates the need for large electrolytic capacitors that are typically used in dc-link ac–ac converters. Moreover, a compact high-frequency transformer at the link can replace the bulky low-frequency transformers, in case isolation is required. These features increase the power density as well as reliability of the proposed converter in comparison with the conventional dc-link converters. The number of required switches in the proposed converter is 12, which is less than the number of switches needed in matrix converters, leading to lower switching and conduction losses. Despite being single-stage, the proposed ac–ac converter is capable of both stepping up and stepping down the voltage and also frequency transformation. This eliminates the need for using cascaded power converters. In this paper, the operation principles of the proposed ac–ac converter are investigated, and variable switching frequency and fixed switching frequency control methods for operating this converter are introduced. The performance of the converter is verified through simulation and experiment. [ABSTRACT FROM AUTHOR]

In this paper, a new structure for a nonisolated boost dc–dc converter is proposed. The proposed converter generates higher voltage gain than some conventional nonisolated boost dc–dc converters. In this paper, the voltage and current equations of the elements and voltage gain in continuous conduction mode and discontinuous conduction mode are extracted. Then, the critical inductance converter is extracted and the current stresses in the switches are calculated. To achieve high voltage gain, a generalized structure based on the proposed structure generates for dc–dc converters. Meanwhile, the root mean square current relations of devices are obtained for an extended structure. Finally, the results of PSCAD/EMTDC software and laboratory prototype are used to reconfirm theoretical concept. [ABSTRACT FROM AUTHOR]

This paper introduces a new bidirectional single-phase inverter topology. The proposed topology has three ports: a dc port, an ac port, and a ripple port. The ac and dc ports are bidirectional to support rectifier or inverter operation. A small inductor, which is of alternating current, exchanges power between different ports of the single-phase system. The proposed topology is capable of accomplishing voltage step-up or step-down, suppressing the ripple power, and performing inversion or rectification operation in one stage of power conversion. The proposed configuration offers an active decoupling function, which not only eliminates the double-frequency ripple power at the dc port but also achieves minimum capacitance requirements to minimize the size of the decoupling capacitor. This facilitates the use of a very small thin-film capacitor, which offers a much longer life-cycle and higher reliability compared with a bulky electrolytic capacitor. A control approach is also developed to regulate the dc-port and ac-port currents and manage the ripple power through proper distribution of power between each port. Moreover, a very small capacitor can be placed in parallel with the inductor to reinforce the proposed configuration with soft-switching operation, which enhances the overall efficiency and minimizes the voltage stress over the semiconductor devices. This converter is capable of accommodating an arbitrary number of dc or single-phase ac sources and/or loads configuring a multiple-input multiple-output inverter without introducing any additional passive elements or sacrificing the performance of the inverter. The primary focus of this paper is dc-to-ac conversion mode of operation, in spite of the fact that it can easily be configured to serve as a rectifier. Experimental and simulation results are presented to validate the operation of the proposed topology and its control strategy. [ABSTRACT FROM AUTHOR]

Most of the two-stage converters for electric bike battery charging comprise of a boost converter for power factor correction (PFC) followed by a dc–dc converter with universal input voltage. These two-stage conversions suffer from poor efficiency and increased component count. In this paper, a single-stage switched inductor Cuk converter based PFC converter is proposed, which offers high step-down gain, low current stress, high efficiency, and reduced component count. The operational analysis and design equations for various components of the proposed converter are carried out in continuous current mode. This paper presents mathematical modeling, analysis, simulation, and experimentation on the proposed converter rated for 500 W, 48 V/10.4 A. The performance investigation of the proposed converter with respect to power quality indices like voltage total harmonic distortion (THD), current THD, and total power factor is carried out with various types of loads such as resistive load and battery load in both constant voltage (CV) and constant current (CC) mode. Furthermore, the dynamic performance of the proposed converter with battery charging is investigated in CV mode and CC mode with respect to the wide range of supply variations. [ABSTRACT FROM AUTHOR]

This paper presents a unified framework for the modeling, analysis, and design of load-independent Class E and Class EF inverters and rectifiers. These circuits are able to maintain zero-voltage switching and, hence, high efficiency for a wide load range without requiring tuning or use of a feedback loop, and to simultaneously achieve a constant amplitude ac voltage or current in inversion and a constant dc output voltage or current in rectification. As switching frequencies are gradually stepping into the megahertz (MHz) region with the use of wide-bandgap (WBG) devices such as GaN and SiC, switching loss, implementing fast control loops, and current sensing become a challenge, which load-independent operation is able to address, thus allowing exploitation of the high-frequency capability of WBG devices. The traditional Class E and EF topologies are first presented, and the conditions for load-independent operation are derived mathematically; then, a thorough analytical characterization of the circuit performance is carried out in terms of voltage and current stresses and the power-output capability. From this, design contours and tables are presented to enable the rapid implementation of these converters given particular power and load requirements. Three different design examples are used to showcase the capability of these converters in typical MHz power conversion applications using the design equations and methods presented in this paper. The design examples are chosen toward enabling efficient and high-power-density MHz converters for wireless power transfer (WPT) applications and dc/dc conversion. Specifically, a 150-W 13.56-MHz Class EF inverter for WPT, a 150-W 10-MHz miniature Class E boost converter, and a lightweight wirelessly powered drone using a 20-W 13.56-MHz Class E synchronous rectifier have been designed and are presented here. [ABSTRACT FROM AUTHOR]

To support the development of high-frequency ac microgrids in terms of compact design, high-voltage gain and low total harmonic distortion (THD), a buck–boost dual-leg-integrated step-up inverter is proposed in this paper. The inverter is formed by integrating a buck–boost converter into a conventional single-phase full-bridge inverter by sharing the upper switch and the body diode of the lower switch in both bridge-legs. Consequently, the component count is significantly reduced over the step-up inverter counterparts. In addition, to address the drawbacks of hybrid modulation methods adopted by existing dual-leg-integrated inverters, such as double-variable control, and high THD of output voltage/current at high input voltage and heavy load conditions, unipolar frequency doubling sinusoidal pulse width modulation scheme is adopted in this inverter. As a result, the modulation ratio M becomes the only control variable to regulate the output voltage/current and the control is simplified. The THD of the proposed inverter output can remain low throughout the entire input voltage range and load power range. This paper presents the topology derivation procedure, operation principle, and steady-state characteristics of the proposed inverter. To validate the effectiveness of theory, experimental results of a 400 W hardware prototype, where the output voltage frequency is at 500 Hz, are reported. [ABSTRACT FROM PUBLISHER]

A switched-capacitor-based dual-switch dc–dc converter with a high-boost voltage gain is proposed in this paper. The proposed converter can obtain a high-voltage gain with a small duty cycle, which decreases the voltage stress and the conduction loss on the power switches. This paper presents the key waveforms, the operating principles at the continuous conduction mode and the discontinuous conduction mode, and the parameter design. Moreover, a comparison between the proposed converter and other nonisolated converters has been completed. To verify the operating principle, a 200 W prototype is constructed with an input voltage of 25–50 V and an output voltage of 200 V. The simulation and experimental results are shown. [ABSTRACT FROM PUBLISHER]

This paper proposes a new bidirectional resonant dc–dc converter suitable for wide voltage gain range applications (e.g., energy storage systems). The proposed converter overcomes the narrow voltage gain range of conventional resonant dc–dc converters, and meanwhile achieves high efficiency throughout the wide range of operation voltage. It is achieved by configuring a full-bridge mode and a half-bridge mode operation during each switching cycle. A fixed-frequency phase-shift control scheme is proposed and the normalized voltage gain can be always from 0.5 to 1, regardless of the load. The transformer root-mean-square (rms) currents in both the forward and reverse power flow directions have a small variation with respect to the voltage gain, which is beneficial to the conduction losses reduction throughout a wide voltage range. Moreover, the power devices are soft-switched for minimum switching losses. The operation principles and characteristics of the proposed converter are firstly analyzed in this paper. Then the analytical solutions for the voltage gain, soft-switching, and rms currents are derived, which facilitates the parameters design and optimization. Finally, the proposed topology and analysis are verified with experimental results obtained from a 1-kW converter prototype. [ABSTRACT FROM PUBLISHER]

This paper presents a hybrid nonisolated dc–dc commutation cell, which is generated by the integration between conventional commutation cell and ladder-type passive switched capacitor (SC) cell. From the resulted hybrid cell are derived three different dc–dc converters: a buck-type, a boost-type, and a buck–boost-type. The three structures are analyzed in this paper and are presented the topological stages, static gain characteristics in continuous conduction mode and discontinuous conduction mode, steady-state analysis. The analyses are generalized in relation to the number of switched-capacitor cells employed, which allows the increase of the rated gain of the converters by adding more SC cells. In addition, the proposed hybrid nonisolated dc–dc commutation divides naturally the voltage stress among the semiconductors and capacitors of the power stage. A 1-kW prototype was developed to verify the operation of the three proposed converters and their theoretical analysis. For the buck-type topology, designed with an input voltage of 600 V and output voltage of 450 V, a peak efficiency of 99.2% and efficiency at rated power of 99% were obtained. [ABSTRACT FROM PUBLISHER]

This paper presents a design method for a resonant class-DE rectifier with a shunt inductance input network. The cass-DE resonant rectifier offers numerous advantages at high operating frequencies and high output voltages. For a high-voltage design, the limiting factor has been the absence of a design process incorporating shunt inductance for low-to-high impedance matching as well as nonlinear capacitance from semiconductor devices. To design a rectifier with a specific input impedance at the fundamental frequency of operation, designers have been relying on either parametric variation in iterative simulations that often takes a long time to complete, or simple equations without considering nonlinear capacitances that renders the analysis inaccurate at high frequencies. In this paper, we propose a design procedure that begins with universal design curves that are applicable regardless of the capacitance nonlinearity. This is followed by parameter selection and a convergence check to ensure the rectifier operates at the desired output voltage. Based on the outlined procedure, we design and experimentally verify a 27-MHz 350-V current-driven rectifier, a 25-MHz 500-V voltage-driven rectifier, and a 27.12-MHz 2-kV four-stage rectifier, all of which the resonant capacitor is nonlinear and the input impedance is resistive at the switching frequency. [ABSTRACT FROM PUBLISHER]

The subject of this paper falls under the development of power electronics for more electric aircraft systems. The study concerns the design of a converter whose function is to generate a 300-V dc bus from a standard 28-V dc avionic network. Various systems, such as motor drives, need to be connected to the 28-V dc network. Their design could be simplified significantly, and standardized, by introducing this intermediate 28–300-V stage. The step-up converter in the proposed configuration is integrated as a part of the system. The power specification is 10 kW, which leads to very high-current values on the 28-V side. The choice of the converter topology, therefore, needs to match this central constraint. The proposed converter uses six boost cells, associated to constitute a series–parallel architecture. This arrangement leads to significantly more optimal sizing for high step-up ratios than conventional boost-cell configurations. Cell interconnection is implemented by means of a monolithic InterCell transformer to reduce the weight of the magnetic part. This paper describes the topology, design, and construction of the lab prototype, as well as experimental results obtained during testing. [ABSTRACT FROM PUBLISHER]

In this paper, a new zero voltage zero current transition (ZVZCT) boost DC–DC converter using a coupled inductor is proposed. This topology provides the main switch ZVZCT for the turn-on and zero voltage switching (ZVS) for the turn-off. Moreover, the auxiliary switch turns on at zero current switching (ZCS) and turns off at ZVS. The main diode turns on with ZVT and turns off with ZCS, and other diodes also operate under soft-switching conditions. Besides, due to the coupling effect, the proposed converter improves efficiency additionally since resonant energy in the resonance tank could be transferred to the output, and the circulating current can be limited as well. The soft-switching can be realized in almost all the load rang. In this design, there always exist energy releasing circuits to conduct magnetic flux leakage currents, such that the surge currents are eliminated and switch current stress can be accordingly reduced. All the devices resonate in a unique direction within less than half of a resonance period, so power losses with respect to the resonance can be decreased. In this paper, the converter design and operation principles of the converter are given. It also has been verified by a 1-kW experimental prototype with switching frequency of 100 kHz, and the related experimental results are presented. [ABSTRACT FROM PUBLISHER]

An extended-duty-ratio (EDR) boost converter is studied extensively in this paper for high voltage gain applications with a wide input (and/or output) voltage range. The EDR is a unique combination of an interleaved, multiphase boost converter and switched capacitor configuration that achieves high voltage gain with significantly lower switch voltage stress and switching losses compared to conventional high-gain solutions. Most of the switches in the multiphase EDR experience only a fixed fraction of the output voltage ($1/M, 2/M$ , etc., where $M$ is the number of phases). Through extensive analysis over a wide operating range, it is shown here that the EDR boost converter has inherent current sharing among the phases only in a limited range of duty ratio— $(M-1)/M \leq D \leq 1$. As the duty ratio reduces beyond this range as required in wide input voltage applications, inherent current sharing property is lost. In this paper, techniques to ensure current sharing under all operating zones without requiring current sensors are presented. Instead of having equal duty ratio for each phase, it is adjusted for each phase according to the operating region of the converter. Extensive analysis is presented to derive the required duty ratio changes for the different phases. The proposed concept is validated with experimental results from a 250 W, 3-phase EDR boost, and GaN-based hardware prototype. [ABSTRACT FROM AUTHOR]

A new static synchronous compensator (STATCOM) based on the diode-clamped modular multilevel converter (DCM2 C) is proposed in this paper. In this converter topology, the capacitor voltage is clamped by using a low power rating diode in each submodule. The quantity of voltage sensors is significantly reduced and is free from the number of voltage levels. Furthermore, the voltage balancing control method becomes very simple and the capacitor voltage balance speed is fast. Based on the structure of modular multilevel converter, the DCM2C-STATCOM has the capability of Var compensation and negative-sequence current compensation. The topology characteristics and compensation control method of DCM2C-STATCOM are investigated in this paper. Experimental results obtained from a laboratory prototype validate that the capacitor voltage of the proposed DCM2C-STATCOM can be well balanced and the Var and negative-sequence current compensations are effective. [ABSTRACT FROM AUTHOR]

Renewable energy generations have been attracting sustained attentions in academic and industry. Current-fed-isolated-bidirectional dc/dc converters (CF-IBDCs) are widely adopted in low-voltage high-current applications such as solar photovoltaic fuel cell with energy storage. This paper gives an overview and a comprehensive comparative evaluation of CF-IBDCs. The active clamped, dual half-bridge, L-L type dual active bridge, resonant-type, naturally clamped, and other type topologies of CF-IBDCs are investigated, analyzed, and compared regarding their circuit topological structures, operation characteristics, modulation methods, and soft-switching technologies. In addition, component cost models and loss models of converters are deduced and presented. On this basis, quantitative and comprehensive performance comparison of seven typical CF-IBDC topologies selected from each type is conducted in terms of costs, losses, weight, volume, and power density for the given system specifications and design constraints. Finally, the application range of different CF-IBDCs and future trend are presented to encourage further development. [ABSTRACT FROM AUTHOR]

In this paper, a novel topology combining reconfigurability and hybridization is presented. Reconfigurability allows the proposed converter to operate in three different operating modes, yielding a wide range of step-up conversion ratios. The combination of two charge-pump cells and an inductor allows to reduce the average inductor current if compared to a standard equivalent boost converter. A prototype with integrated MOS, drivers, and logic but external passives was built. Experimental results show that with $\mathbf {f_{s} }=\text{300}\,$ kHz, $\mathbf {V_{in} = \text{6}}\,$ V, and $\mathbf {I_o = \text{70}}\,$ mA, the converter can cover conversion ratios in the range from $\text {2.5}$ to $\text {10}$ , with a maximum output voltage equal to $\text {60}\,$ V. Peak efficiency is $\text {91}$ %. When the output current is increased to $\text {100}\,$ mA peak efficiency is $\text {92.8}$ %. [ABSTRACT FROM AUTHOR]

This paper presents a new single-phase ac–dc–ac three-level three-leg converter composed of three coupled-inductors and six active switches. The system model, operation principles, and a control strategy are presented and discussed. Additionally, a space-vector pulsewidth modulation technique is developed to double the effective frequency of the grid and load voltages and to reduce the switching losses. The proposed converter is compared to other similar converters in terms of switch count, harmonic distortion, and power losses. The results show that the proposed topology has improved power quality and uses fewer switches and gate drive circuits. These characteristics can potentially reduce the costs and the complexity of the system. In addition, the proposed converter eliminates the requirement for dead time to prevent short circuit of the dc-link. In order to validate the theoretical analysis, simulated and experimental results are presented and discussed. [ABSTRACT FROM AUTHOR]

In this paper, a novel topology of modular dc–dc converter has been proposed for medium voltage dc (MVdc) integration of high-penetration distributed PV. The proposed topology is featured with input-independent and output-series connected configuration and intermodule power balancing units (PBUs). A high voltage gain could be achieved with series-connected submodules (SMs), while each SM's input port is connected with PV array to realize the independent maximum power point tracking (MPPT) control function. PBUs with bidirectional power conversion ability are installed between adjacent SMs for the elimination of intermodule power mismatch. The operation principles of the proposed converter have been explained in detail along with the corresponding control strategies. The design principles of major passive components have been investigated on the basis of boundary operation conditions, while a quantitative analysis of steady-state power losses has been performed. Moreover, a comparative study is conducted from the aspects of operation range, topology complexity, component stress, and power efficiency. The theoretical results have been validated by both simulations and down-scaled experiments. [ABSTRACT FROM AUTHOR]

This paper introduces the high-frequency link concept into the modular multilevel converter (MMC) topology, which can totally reduce the individual dc-link capacitors at the high-voltage side. The proposed converter, called isolated MMC, has basic triple ports of medium-voltage ac, medium-voltage dc, and low-voltage dc. Thus, it is especially suitable for hybrid dc and ac applications in power generation and transmission, such as solid-state transformer. The fundamental principle and applied control scheme of phase-shift pulsewidth modulation are presented in detail. The design of the voltage clamping circuit and analysis of duty loss are carried out. The experimental results are given to illustrate the efficient operation characteristics. [ABSTRACT FROM AUTHOR]

In this paper, a dual half-bridge LLC resonant converter with magnetic control is proposed for the battery charger application. The primary switches are shared by two LLC resonant networks, and their outputs are connected in series. One of the LLC resonant converters is designed to operate at the series resonant frequency, which is also the highest efficiency operating point, and the constant output voltage characteristic is achieved at this operating point. The second LLC resonant converter adopts magnetic control to regulate the total output current and voltage during both constant current charge mode and constant voltage charge mode. Meanwhile, the function decoupling idea is adopted to further improve the system efficiency. The significant amount of the power is handled by the LLC resonant converter operating at the series resonant frequency, whereas the second LLC resonant converter fulfills the responsibility to achieve closed-loop control. By carefully designing the resonant networks, the zero-voltage switching for primary switches and zero-current switching for secondary diodes can be achieved for whole operation range. A 320-W experimental prototype is built to verify the theoretical analysis, and the maximum efficiency is measured about 95.5%. [ABSTRACT FROM AUTHOR]

The Cuk dual resonance core (DRC) realizes overlapped dual resonance to regulate its output voltage. However, the DRC configuration was only applied to the Fibonacci switched-capacitor converter (SCC), series–parallel SCC, and voltage doubler. In this paper, the Cuk DRC is modified and then is extended to the Dickson SCC to form a multi-resonance-core-based (MRC) Dickson resonant switched-capacitor converter. All charging and discharging loops achieve soft charging, and so the inherent capacitor charge sharing loss and the high current transient spikes are eliminated. The modular configuration makes the MRC Dickson easy to be extended to a higher voltage level. The on-time fixed frequency modulation is adopted, all transistors being turned on with zero-current-switching (ZCS) operation and all diodes being turned off with ZCS operation. Most importantly, the conversion ratio of the MRC Dickson can be regulated continuously, widely, and efficiently even at light load condition, which is a huge advantage over the traditional Dickson SCC with limited control headroom. A comprehensive analysis of the operation principle, voltage-gain curve, component stress analysis, and output characteristic is provided. The converter operation principle and regulation capability were verified by both simulation and experiment. [ABSTRACT FROM AUTHOR]

Load-independent output characteristics of inductive power transfer (IPT) systems are increasingly popular in battery charging. This paper proposes a novel variable-parameter T-circuit (VT) for an IPT system charging a battery with constant current (CC) or constant voltage (CV) output. The VT can transfer a CC/CV input to a CC or CV output by using an ac switch and a passive component (inductor or capacitor). An IPT system with a VT for CC–CV charging can reduce the number of passive components and ac switches. Besides, the proposed VT merits more design freedom of charge current/voltage with the constraints imposed by the loosely coupled transformer parameters compared to that of the traditional one. In addition, there are three kinds of VTs for various IPT charging systems with different requirements. A 400 W laboratory-scale prototype with a 150 mm air gap was built to verify the theoretical analyses. Both electronic load and lead-acid battery are utilized to verify the charging profile of the proposed method. The experimental results of the IPT system indicate that the fluctuation of the charging current in CC mode is less than 2%, and the change rate of charging voltage in CV mode is within 2.9%. The maximum overall efficiency 93.93% of the charging system is achieved from a dc 110 V input to a dc 100 V output. [ABSTRACT FROM AUTHOR]

In voltage-source converter systems, utilization of filter inductors with deep saturation characteristics is often advantageous because of the improved size, cost, and efficiency. However, with the use of conventional current regulation methods, the inductor saturation results in significant dynamic performance loss and poor steady-state current waveform quality. This paper proposes the saturation compensation with resistive decoupling (SCRD) method to overcome these performance issues. The method converts the nonlinear inductor of the plant to a fictitious linear inductor such that linear current regulators can perform satisfactorily. The steady-state and dynamic performances of SCRD are investigated in detail in comparison with other methods and advantageous performance attributes of SCRD are demonstrated on a 1.5-kW grid-connected system via simulations and laboratory experiments. In addition, identification of L–R parameters is performed, parameter sensitivity issues are addressed, and satisfactory performance is demonstrated. [ABSTRACT FROM AUTHOR]

Improving the power density of a power converter has many benefits for systems integration. Aspects such as thermal management, weight, conformation to mounting locations, and the footprint of the converter all become critical factors as systems continue to scale down in size. The flying capacitor multilevel converter topology is of interest because it has characteristics which contribute to high power density. This paper presents a quasi-square-wave zero-voltage switching (ZVS) multilevel dc–dc converter. ZVS greatly reduces switching losses and enables high-frequency operation of the converter. A hardware prototype is implemented, built on a flexible polyimide substrate circuit board. Experimental results show a peak system efficiency above 98.1%, an effective switching frequency of up to 3 MHz, and a power output of 250 W. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) systems having rechargeable batteries are prone to be complex and costly because multiple converters are necessary to individually regulate a load, PV panel, and battery. This paper proposes novel nonisolated multiport converters (MPCs) integrating a bidirectional pulsewidth modulation (PWM) converter and phase-shift-switched capacitor converter (PS-SCC) for standalone PV systems. A PWM converter and PS-SCC are integrated by reducing the total switch count, realizing the simplified system and circuit. In the proposed MPCs, two control freedoms of duty cycle and phase shift angle are manipulated to individually regulate the load, PV panel, and/or battery. The detailed operation analysis was performed to mathematically derive gain characteristics and zero voltage switching operation boundaries. For the battery discharging mode, in which the PV panel is not available and the MPC behaves as a single-input–single-output converter with two control freedoms available, the optimized control scheme achieving the lowest rms current is also proposed to maximize power conversion efficiencies. Various kinds of experimental verification tests using a 200-W prototype were performed to verify the theoretical analysis and to demonstrate the performance of the proposed MPC. [ABSTRACT FROM AUTHOR]

This paper presents a new bridgeless buck–boost power factor corrector with the use of the active virtual ground technique, which is named as the Manitoba Rectifier. The proposed topology can convert the grid ac voltage into a wide range of voltage outputs within a single-stage circuit. It is in a bridgeless structure and simple in design. During the operation, an LC filter is generated at the system input, where continuous grid current is guaranteed in a buck–boost characteristic topology. In addition, the filter capacitor helps to clamp the voltage ripple between the grid and the output bus terminal. Both leakage current and common mode noise are kept in a relatively small value. Thus, a single-stage and low common-mode buck–boost converter system is built. The proposed topology is successfully implemented on an 800 W prototype, and the performance is experimentally verified, which shows good agreement with the theoretical findings. [ABSTRACT FROM AUTHOR]

The three-level full-bridge (TLFB) dc−dc converter has been widely used in high-voltage, high-power applications. In the experimental test, the neutral-point voltage deviation appears; moreover, it has also been found out that if the flying capacitors are introduced, the input capacitor voltages could realize self-balance even if no active balancing solutions are adopted. In the previous publications, the role of flying capacitors is generally considered to extend the range of soft switching; however, the self-balance ability has not been mentioned or investigated in any publications thus far. In order to fill this gap, this paper provides the detailed mode operation analysis of the TLFB converter and reveals the cause of the imbalance. In addition, the mechanism of the self-balance ability provided by the flying capacitors is explained in detail, which gives a deep insight into the converter. At last, the influence factor of the voltage error in steady state has been analyzed, and the specific expression of the voltage error is also derived. The feasibility of the theoretical analysis is verified by the simulation and experimental results. [ABSTRACT FROM AUTHOR]

In this paper, a family of three-port three-level converters (TPTLC) composed of asymmetrical bidirectional half-bridge modules is proposed, which offers the benefits in terms of a simple control scheme, extended soft switching over a wide range of operating conditions, and reduced voltage stress across switches. The proposed converters take advantage of a pulsewidth modulation plus phase shift control technique to regulate the output voltage as well as to control the power flow between different ports independently. A stacked TPTLC is taken as an example to be introduced in detail to gain a thorough insight into the proposed family of converters. The stacked TPTLC can provide a high voltage gain along with a wide voltage gain range without using any transformer, resulting in the improvement in the power density. In order to minimize the conduction loss and reduce the current stress of switches, the root-mean-square current of the inductor and the boundary condition of the phase-shift controller in different operation scenarios are studied. Finally, the feasibility of the proposed concept and effectiveness of the design approach are validated based on the experimental results of a 1-kW, 100-kHz prototype of the stacked TPTLC using gallium nitride switches. [ABSTRACT FROM AUTHOR]

Due to its simplicity, the hard-switching boost converter is widely used in many applications, such as renewable energy and power factor correction. The power density of the converter can be increased with smaller magnetics; however, this requires an increase in the switching frequency. Therefore, it is necessary to provide soft-switching conditions to minimize the switching losses. In this paper, a new resonant step-up converter and the associated analysis are presented. The proposed interleaved LC resonant boost converter provides soft switching for all of the semiconductor elements even under light loading conditions. Small inductors with discontinuous conduction mode (DCM) currents can be used because the interleaving behavior ensures a continuous input current with low ripples. The interleaving also reduces the output capacitor ripple current. Burst mode operation has been applied to improve the efficiency of the converter during light loading conditions. Detailed design methodology and the control strategies are provided. To show the validity of the theoretical analysis, experimental results are provided for a 400-W prototype, and are compared to a benchmark conventional interleaved boost converter with the same components. Substantial efficiency improvements are achieved for different loads and voltage gains, particularly under light loading conditions. [ABSTRACT FROM AUTHOR]

This paper describes a theory to synthesize nonisolated dc–dc converters. It uses the fundamental flux balance equation across the inductors of a converter as a starting point in this synthesis process. The flux balance equations are the linear equations of the input voltage, capacitor voltages, and duty cycle (D). The coefficients of these linear equations can be selected from a finite set of choices. These choices define the converter topologies that are subsequently used to synthesize a converter. The synthesis procedure applies to a converter of multiple order. All the possible converters are identified for a first-order topology. In the case of second-order converters, all the choices of the flux balance equation are defined. Based on these choices, three new quadratic topologies are derived and verified to demonstrate the effectiveness of the theory. The procedure to synthesize a converter from a given voltage conversion ratio is also outlined. [ABSTRACT FROM AUTHOR]

High step-up boost converters with coupled inductor have attracted much attention in the fuel cell or photovoltaic grid-connected generation system, however, there are few literatures elaborated on the construction ideas and derivation methods of them. Accordingly, in order to obtain a clear roadmap on the derivation and inner connection of these converters, a comprehensive review and analysis are presented in this paper. First, the basic boost converter with coupled inductor is regarded as the basic topology, and its merits and demerits are analyzed in detail. Then, in order to address these demerits, various step-up techniques are introduced, such as the rectifier circuit, the active-clamped circuit, the multi-winding coupled inductor, and the voltage doubler rectifier; and numerous new topologies are continuously proposed by combinations and equivalent simplifications. In addition to a detailed synthesis of each topology, a comparative and quantitative analysis among some important converters is presented, and the optimal one is chosen to build a 250 W prototype. Finally, based on comparisons and analysis, the main characteristics and inner connections of these high step-up boost converters with coupled inductor are identified and clarified. [ABSTRACT FROM AUTHOR]

This paper presents a single-stage single-switch soft-switching (S6) power factor correction (PFC) converter to enhance the current shaping performance and reduce the total harmonic distortion. This improvement is achieved by the aid of an auxiliary winding which is used to lower the input current harmonics and also achieve soft-switching condition. As a result, the switching losses are reduced and harmonic content of the input current is improved noticeably in comparison to the conventional S6 PFC converter. Also, the total number of semiconductor elements is reduced in the proposed topology which results in lower cost and higher efficiency. The operating modes of the proposed converter are discussed in detail and the design procedure is presented. A 200-kHz prototype of the proposed converter is implemented and the obtained results are provided to verify the converter theoretical analysis and operation. [ABSTRACT FROM AUTHOR]

In order to provide high and extendable power levels for inductive power transfer (IPT) system, a parallel multi-inverter system based on modular inverter is presented. Various power requirements can be implemented by an adjustment of the number of paralleled inverters, which provides a high modularity. A master−slave scheme is employed for the switching-driver signals of parallel inverters, where one acts as a leader while others act as followers. Despite the master−slave scheme, the proposed circuit topology has natural robustness because of the equality in terms of the hardware configuration of each modular inverter. For proper parameters, the output phase (current lagging corresponding voltage) of an inverter is lower than the average of output phase of all inverters, when its output voltage lags behind others, and vice versa. Based on this approach, PI controllers are designed to implement phase synchronization for output voltages of all inverters. An IPT prototype supplied by the proposed parallel multi-inverter with three inverters was designed, built, and tested. Experiments show that the proposed parallel multi-inverter system has not only good circulating current suppression capacity but also excellent performance of phase synchronization. The maximum dc−dc efficiency was 94% at a 35.1 kW receiving power. This paper is accompanied by a Matlab/Simulink file demonstrating phase synchronization control. [ABSTRACT FROM AUTHOR]

This paper contains a comparison between three topologies of a three-phase two-level inverter: A quasi-Z-source inverter (qZSI), a voltage-source inverter with a boost converter and a voltage-source inverter with an interleaved boost converter. experimental results obtained from laboratory tests of equivalent 6-kW 100-kHz inverters based on SiC mosfets and Schottky diodes are provided. The following parameters are compared: Quality of input inductor current and output phase voltage as well as total power losses in the inverters. The results for these parameters are obtained for input voltage ranging from 325 V to almost 600 V (where feasible), for two sets of equivalent modulation methods (two regular methods and two reduced-loss methods), for a couple of characteristic values of deadtime and for the operation both at the maximum value of modulation index and at equal values of voltage across the inverter bridge. Results of the experiments show that the qZSI topology may, at certain conditions, surpass the traditional two-stage inverter topologies in the areas of input inductor current quality, output voltage quality and also power losses (at high values of input voltage). What is needed to obtain that is a careful examination of operating conditions, applied modulation method and deadtime value. [ABSTRACT FROM AUTHOR]

This paper discussed an active-bridge-active-clamp (ABAC) topology that is suitable for highpower more-electric-aircraft applications. Though conventional modulation techniques can be applied to ABAC converters, they present drawbacks, such as increased low-voltage (LV) current ripple and limited power transfer capability. To address these problems, a phase-shift-modulation (PSM) scheme is proposed to provide clean dc terminal current at the LV side while maintaining high power transfer capability and efficiency in a wide operating range. The proposed PSM has a complete switching harmonics cancellation on the LV terminals independent of the operating conditions. This results in high quality power without any ac components, thus minimizing passive filtering. In addition, when terminal voltages vary from their nominal values, the proposed PSM can improve the maximum power transfer capability of the ABAC converter compared to the conventional approach. The theoretical claims are validated by both simulation and experimental results on a 10-kW 270-V/28-V ABAC converter. [ABSTRACT FROM AUTHOR]

In this paper, a new zero-voltage zero-current transition (ZVZCT) boost converter using coupled inductors is proposed. The feature of this topology is: the main switch can be switched on with ZVZCT, and off with zero-voltage switching, without any voltage and current stress. The auxiliary switch is turned on with zero-current switching. Other semiconductor devices can also achieve soft switching (SS). Due to the existence of the coupling effect, the current impact of the auxiliary switch is completely suppressed when it is turned off. Lower input current and output voltage in the interval of the switch-off for the auxiliary switch are just equivalent to running at a low power level, which is an additional advantage of the coupled inductor ZVZCT solution. Another advantage of the topology is that the SS condition of the main switch for each specific load can be effectively optimized just by setting the ratio of coupling inductance corresponding to the circuit design and application load. Thus, the topology design can be improved to adapt to different load types. A 100 kHz experimental prototype has been verified, different load for 1 and 0.4 kW optimization comparison has been presented, and the case without optimization is also observed. [ABSTRACT FROM AUTHOR]

Modules with series and parallel connectivity add new features and operation modes to modular multilevel converters (MMCs). Compared to full- and half-bridges, the series/parallel modules allow sensorless module balancing and reduce conduction loss with the same semiconductor area. However, in high-voltage applications with limited switching rates, the sensorless operation of the series/parallel modules suffers from large charge-balancing currents. This paper introduces a series/parallel module variant with a small port inductor. The port inductor suppresses the charge-balancing current despite low switching rates. We also propose a carrier-based modulation framework and show the importance of the carrier assignment in terms of efficiency and balancing. The proposed module and the modulation method are verified on a lab setup with module switching rates down to 200 Hz. The module voltages are kept within a narrow band with the charge-balancing currents below 5% of the arm current. The experimental results show practicality and advantages of the new series/parallel modules in high-voltage MMC applications. [ABSTRACT FROM AUTHOR]

There have been several advanced topologies proposed by the community for micro-inverter applications. However, many such applications suffer from unwanted second-order harmonic current ripple at dc input. Moreover, in the absence of suitable passive filter or ripple compensator, the second-order harmonics ripple may propagate into the dc source. This results in several problems to the system, related to system efficiency, life, cost, size, reliability, and stability. This paper proposes an adaptive sliding-mode controller to shape the output impedance of the boost-circuit of quasi-switched boost inverter such that the propagation of the ripple from dc link to the dc-input source is resisted. The quasi-switched boost inverter is one of the advanced and suitable topologies for the micro-inverter applications. The adaptive nature of the proposed controller improves the transient performance of the system at the line–load transients unlike some existing solutions, which affects dynamics adversely to achieve ripple mitigation objective. The controller ensures voltage regulation within ${5\%}$ at dc link. The proposed control technique is verified using a lab-prototype of 500 W quasi-switched boost inverter. [ABSTRACT FROM AUTHOR]

In the context of reducing total CO $_2$ emissions as well as reducing the total copper cable length and weight on cars, automotive manufacturers propose to derive all the supply voltages from a single $\text{48 V}$ bus through high step-down ratio dc–dc converters. The series capacitor tapped inductor (SCTI) converter is a promising topology for efficient single-stage step-down conversion from the $\text{48 V}$ bus. In the synchronous version of the SCTI, however, turn-off of the synchronous rectifier at positive drain-to-source current leads to a voltage spike and to a potential catastrophic failure of the converter. In this paper, a simple control technique is proposed, which prevents the foregoing condition to occur. The approach enables a reliable operation of the synchronous SCTI topology without disrupting its main features and advantages, and eliminating the need for additional snubbers, voltage clamps or auxiliary windings. The approach is validated via computer simulations and experimental tests on a $\text{48}$ -to- $\text{1.5}\;\text{V}$ , $\text{4 A}$ SCTI converter prototype. [ABSTRACT FROM AUTHOR]

In this paper, a technique of variable-turns-ratio high-frequency link inverter is proposed to provide a simple method to achieve multi-level outputs for the isolated single-stage high-frequency link inverters. By dynamically adjusting the turns ratio of transformer, five-level (±2, ±1, and 0) outputs can be achieved to improve the current quality. The single transformer, compared with the existing two-level high-frequency link inverter, is employed in the structure and only a few auxiliary devices are added, where the added circuit operates at low frequency and the power density is refined. Based on this technique, the single-stage active clamped forward grid-connected inverter with variable turns ratio is taken as an example to better illustrate the analysis process and a 1000-W prototype is designed and established to evaluate the output performance. The conducted simulation results and prototype tests verify the feasibility of the proposed single-stage variable-turns-ratio high-frequency link grid-connected inverter. [ABSTRACT FROM AUTHOR]

This paper investigates basic stability properties of the three-level flying-capacitor Buck converter when operated under current-mode control (CMC). The proposed analysis is developed for both peak CMC (P-CMC) and valley CMC (V-CMC), and addresses both the static instability of the inductor current and the flying capacitor (FC) voltage runaway phenomenon. Conditions for avoiding current subharmonic oscillations are derived first, along with the expressions of the minimal compensation ramp, which guarantee current stability throughout the entire operating range. As for the stability of the FC voltage, P-CMC results to be inherently unstable unless the converter operates with a relatively large peak-to-peak inductor-current ripple, a feature not yet recognized in the literature. However, V-CMC results to be inherently stable once the static instability of the current is eliminated with an external compensating ramp—a property that has been highlighted in the literature but never formally proven. The proposed analysis is verified both using a simulation model and experimentally using a 3.3-V, 500-mA, 500-kHz prototype. [ABSTRACT FROM AUTHOR]

For the conventional PFC rectifiers, the high efficiency cannot be achieved over a wide input range, and the efficiency will be greatly decreased at low-input voltages. In order to overcome the efficiency bottleneck under low-line input, a flexible mode bridgeless boost power factor correction (PFC) rectifier is proposed in this paper. According to the input voltage, the proposed rectifier can be flexibly adapted to the suitable operating mode to obtain the maximum efficiency. Meanwhile, the circuit components can be reused by different operating modes, so the extra cost is low. In the proposed rectifier, a back-to-back bridgeless boost PFC topology is adopted at high-line conditions and a three-level bridgeless boost PFC topology is rebuilt to reduce the switching losses at low-line conditions. Compared with the traditional bridgeless boost PFC rectifier, an extra low-voltage bidirectional switch (usually composed of two switches) is added, so the increased cost is low. In addition, the low common-mode noise can be achieved at both high- and low-line conditions due to the direct connection between the input mains and the output electrolytic capacitor. The detailed principle analysis about the proposed rectifier is presented in this paper. Finally, an experimental prototype is built to verify the feasibility and the effectiveness of the proposed topology. [ABSTRACT FROM AUTHOR]

Impedance-source networks are an increasingly popular solution in power converter applications, especially in single-stage buck–boost power conversion to avoid additional front-end dc–dc power converters. In the survey papers published, no analytical comparisons of different topologies have been described, which makes it difficult to choose the best option. Thus, the aim of this paper is to present a comprehensive analytical comparison of the impedance-source-based buck–boost inverters in terms of passive component count and semiconductor stress. Based on the waveform of the input current, i.e., with or without a transformer, and with or without inductor coupling, the impedance-source converters are classified. The main criterion in our comprehensive comparison is the energy stored in the passive elements, which is considered both under constant and predefined high frequency current ripple in the inductors and the voltage ripple across the capacitors. Two-level and multilevel solutions are described. The conclusions provide a “one-stop” information source and a selection guide of impedance-source-based buck–boost inverters for different applications. [ABSTRACT FROM PUBLISHER]

In this paper, the Z-source converter is introduced to power factor correction (PFC) applications. The concept is demonstrated through a wireless power transfer (WPT) system for electric vehicle battery charging, namely Z-source resonant converter (ZSRC). Due to the Z-source network (ZSN), the ZSRC inherently performs PFC and regulate the system output voltage simultaneously, without adding extra semiconductor devices and control circuitry to the conventional WPT system such as conventional PFC converters do. In other words, the ZSN can be categorized as a family of the single-stage PFC converters. In addition, the ZSN is suitable for high-power applications since it is immune to shoot-through states, which increases reliability and adds a boost feature to the system. The ZSRC-based WPT system operating principle is described and analyzed in this paper. Simulations and experimental results based on a 1-kW prototype with 20-cm air gap between the system primary and secondary sides are presented to validate the analysis and demonstrate the effectiveness of the ZSN in the PFC of the WPT system. [ABSTRACT FROM PUBLISHER]