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This paper proposes a new fault-tolerant strategy for the purpose of revamping the performance of three-phase multilevel (ML) converters with faulty switches. The proposed fault-tolerant strategy is based on an adaptation of the modified space vector modulation (SVM) technique to the fundamental phase-shift compensation method. The proposed fault-tolerant strategy generates balanced line-to-line voltages with increased voltage levels in the faulty condition. In this paper, first a brief background about cascaded H-bridge (CHB) ML converters and SVM technique is provided. Then the proposed fault-tolerant strategy and the modified SVM technique are presented. Finally, several experimental results are provided to validate operation of the proposed strategy. [ABSTRACT FROM AUTHOR]

This paper presents concepts and results of an investigation of power electronic thyristor-based switched-capacitor voltage multipliers (SCVMs). A concept of the SCVM power converters assumes the utilization of resonant circuits for the zero-current switching operation. The topology makes it possible to apply thyristors as active switches that create the possibility of composing the resonant switch-mode converters for high-voltage gain, high power, and low cost, and opens a huge area of applications. This paper presents an in-depth analysis of the SCVM configured as the resonant high-power thyristor-based converter. The operation with regard to the specific switching conditions of thyristors, as well as efficiency of the converter is analyzed providing the unique relationship important for the converter design, optimization, and efficiency improvement. An experimental validation confirms the feasibility and the operation concept of the SCVM and demonstrates the efficiency range. The SCVM converter can be optimized to the topology with a decreased number of switches. This paper also presents a novel topology of the resonant converter with a reduced number of switches, resonant switched capacitor voltage multiplier (RSCVM), dedicated for thyristor implementation. The RSCVM requires the specific component selection and control. The analysis of the configuration, operation, efficiency, and component selection of the RSCVM converter, as well as simulation and experimental results are presented. [ABSTRACT FROM AUTHOR]

Pulse-width-modulated (PWM) converters have been widely applied for power processing, and they are typically the stems of other types of converters, such as quasi-resonant, Z-source, and switched-inductor hybrid converters. Development of PWM converters has been spanning over a century, starting from the buck converter. The well-known PWM converters include buck, boost, buck–boost, Ćuk, single ended primary inductive converter (SEPIC), zeta, Z-source, quasi-Z source, etc. Many attempts have been proposed to develop these converters based mostly on canonical cell concepts and by introducing extra LC filters to the cells. This paper presents an enhancement to the layer and graft schemes by introducing the ideas of dc voltage/current offsetting, capacitor/inductor component splitting, diode grafting, and inverse operation of PWM converters. The PWM converters, which can be operated in continuous conduction mode (CCM) or discontinuous conduction mode (DCM), therefore can be synthesized systematically according to decoded transfer gains. Decoding and synthesizing PWM converters uniquely bridge transfer gains to converter topologies and provide readers a comprehensive understanding of PWM-converter evolution from the original converter, the buck converter. Additionally, in this paper, the Ćuk, SEPIC, and zeta converters all with the same transfer gain of $D/(1 - D)$ are proved to be equivalent to the buck–boost converter with an extra LC filter. For further illustrating the proposed approaches, various types of Z-source converters, switched-capacitor/switched-inductor hybrid converters, and a single-stage interleaved converter are reviewed, and new PWM converters are developed. [ABSTRACT FROM AUTHOR]

The increasing interest in multiphase drive systems has led to the extension of inverter topologies and pulse width modulation (PWM) methods from three-phase to multiphase occasions. Carrier-based PWM (CPWM) dominates space vector PWM when the phase number increases, because of its simple computation and modular implementation. Although intensive work has been done on modifying PWM methods to reduce the common-mode voltage (CMV), not enough work has been done on CPWM methods with CMV reduction for multiphase drives. This paper extends the phase-shifted sinusoidal PWM (PS-SPWM) method for five-phase and six-phase two-level voltage-source inverters (VSI) and employs the intersection-plotting method and Fourier analysis to reveal the nature of the CMV. Both experiment and simulation results comply with theoretical analysis that compared with the conventional SPWM, the PS-SPWM can effectively reduce the CMV in peak-to-peak value and RMS value, though it leads to a higher phase current distortion. In addition, the hardware realization of PS-SPWM for multiphase inverters by a distributed control system is presented in this paper. [ABSTRACT FROM AUTHOR]

This paper presents a novel interleaved high-conversion-ratio bidirectional dc–dc converter based on switched capacitors and coupled inductors. Series-connected switched capacitor and inductor cells were used to increase the voltage conversion ratio, reduce voltage stresses on power switches, realize soft-charging/discharging of switched capacitors, and achieve autocurrent-sharing in parallel inductors. The interleaved structure combined with switched capacitors was adopted to reduce current ripple at the side having lower voltage, thus enabling applications that require high power levels. In this paper, we first review the status of high-voltage-ratio bidirectional dc–dc converters. Then, the evolution of the proposed extensible topologies and the steady-state operating principle under the inductor current continuous conduction mode is presented. Finally, the performance and features such as voltage gain, voltage and current stress, and the autocurrent-sharing mechanism that are realized by switched capacitors are verified; the optimal design of coupled-inductors, switched-capacitors, and the chip size of switches are given. A specific design of the driving circuit that facilitates actual applications is described. A 1-kW prototype converter, employing a hybrid configuration of SiC and Si mosfets, was constructed to verify the theoretical analysis, and achieved an optimal compromise between conversion efficiency and low cost. [ABSTRACT FROM AUTHOR]

In this paper, a new approach to regulate the output voltage of a resonant, constant voltage transfer ratio 380 V/48 V isolated dc–dc converter is presented. Rather than applying variable frequency control to the resonant converter, which would result in reactive power processing and a more complicated electromagnetic compatibility filter design, the converter remains in its optimal operating point all time and an additional partial-power (PP) processing auxiliary converter is used to tightly regulate the output voltage. The PP converter, supplied through a tertiary winding of the resonant converter's transformer, regulates the output by adding or subtracting voltage from the dc input and has only a marginal impact on the overall efficiency of the dc–dc converter. The principal of operation is explained in detail including Sankey diagrams to illustrate the power processing of the converter and a feedback control system is proposed to tightly regulate the 48 V output voltage. A hardware demonstrator rated at 1.5 kW is implemented to cope with input voltage variations between 340 and 420 V and experimental results are provided showing that the output voltage can be kept within $\pm {1}{\%}$ of the nominal 48 V even under harsh input voltage and load transients. The realized dc–dc converter with PP pre-regulation features an overall efficiency of 97.7 $\%$ at rated power and a power density of 8.6 kWdm $^{-3}$ (141w/ $^{3}$ in). [ABSTRACT FROM AUTHOR]

This paper proposes a topology combination scheme to achieve wide-range operation for LLC resonant converters. Instead of directly adding an auxiliary current injection circuit for each individual LLC converter, the proposed scheme combines two LLC converters through coupled resonance. Then, one LLC circuit can be utilized to adjust the equivalent resonant parameters of the other LLC circuit. By only controlling the phase delay between the mosfet bridges, output voltage regulation is properly maintained without changing the switching frequency. Since the total power rating does not change and each converter can share the load, it does not have any extra cost of power components. The advantages of this design include higher power efficiency, smaller size, and optimized utilization of each converter at different load, since both converters can fulfill isolated power conversion with independent control. Also, by taking the benefit of suppressed frequency variation, a smaller leakage inductance and a lower ratio between the leakage inductance and the magnetizing inductance are allowed, so that the coupling of transformer windings and transformer efficiency just improve. In addition to detailed theoretical analysis, experimental results verify the feasibility and effectiveness of the proposed concept. [ABSTRACT FROM AUTHOR]

This paper presents a design procedure and loss estimation for a high-power, medium-voltage series resonant converter (entitled SRC#), intended for application in megawatt medium-voltage dc wind turbines. The converter is operated with a novel method of operation, entitled pulse removal technique, characterized by variable frequency and phase-shift modulation, below the resonant point of the LC tank. A step-by-step design procedure is proposed and circuit component ratings and efficiency are compared for two variants. The new method of operation reduces transformer size to below 50%, whereas losses are kept below 1.5% from zero to nominal power, due to soft-switching characteristics. An experimental setup, rated for 10 kW and 5 kV output was assembled to extract losses and validate the semiconductor loss model. [ABSTRACT FROM AUTHOR]

High step-down dc/dc converters are widely utilized in telecom and modern industrial applications. Due to the high step-down ratio, conventional Buck converter cannot provide satisfactory performance. To solve this problem, quite a few new topologies have been proposed to improve the performance of high step-down dc/dc converters, such as series-capacitor Buck (SC-Buck) converter, 3-level Buck converters, tapped inductor Buck converters, and LLC resonant converters. In this paper, the twice step-down benefit of SC-Buck converter and the zero-voltage switching benefit of series-capacitor tapped Buck (SC-TaB) converter are combined together to propose a new topology: interleaved series-capacitor tapped Buck (ISC-TaB) converter. To analyze the performance of the proposed ISC-TaB converter, the operation principles are discussed and the voltage conversion ratio is derived. In addition, to guide the design procedure and optimization, the current waveforms and voltage waveforms of the proposed ISC-TaB are derived. In order to verify the performance of the proposed ISC-TaB, hardware prototype of the proposed ISC-TaB converter and conventional two-phase series-capacitor tapped Buck converter (2ph-TaB) are designed and tested. The application is targeted at telecom with 48-V input and 3.3 V/20 A output. The test results are compared between these two converters. A peak efficiency of 95.6% is achieved on the proposed ISC-TaB and the efficiency of the ISC-TaB over all load range is at least 1% higher than that of 2ph-TaB. [ABSTRACT FROM AUTHOR]

This paper proposes a novel modular equalization architecture for series-connected electric double-layer capacitor (EDLC) modules, each consisting of multiple cells connected in series. Cell voltages in a module are equalized by an inductive voltage divider (IVD)-voltage multiplier (VM)-based cell equalizer, while module voltages are unified by switched capacitor converters (SCCs). Square wave voltages generated at switching nodes of the IVD-VM-based cell equalizers are utilized to drive the SCC-based module equalizers, realizing the switchless topology of SCC-based module equalizers. The required switch count of the proposed system can be halved compared to conventional systems, allowing simplified circuit. An experimental equalization test for three EDLC modules, each consisting of six cells in series, was performed from an initially voltage-imbalanced condition. Module and cell voltages were equalized at different rates, and the equalization performance of the proposed modular equalization system was successfully demonstrated. [ABSTRACT FROM AUTHOR]

This paper explores the issue of the neutral-point oscillation in the four-leg neutral-point clamped inverter. Such an issue is closely associated with the neutral-point current, so this study models the inverter on the dc side to clarify its relationship and presents a three-dimension pulsewidth modulation to eliminate the neutral-point oscillation. In addition, an offset-injection approach to reducing the neutral-point oscillation is also investigated and discussed. The laboratory test results will validate the analysis of the proposed approach, and a discussion will be presented to evaluate the effectiveness of eliminating the neutral-point oscillation. [ABSTRACT FROM AUTHOR]

In this paper, a nonisolated high step-up dc/dc converter, belonging to the family of reduced redundant power processing converters (R2P2), is investigated for high-power applications. The selection of this topology as the most suitable for such applications among those belonging to the R2P2 family is justified. Emphasis is given on the theoretical analysis of the real step-up voltage ratio of the converter, and voltage and current stresses under continuous and discontinuous conduction modes of operation, taking into account the nonideality of the topology components, namely the parasitic resistances of semiconductor devices and inductors and the voltage drop of diodes. The theoretical analysis and the behavior of the selected converter are experimentally validated through a 2 kW prototype. Moreover, the overall efficiency of the chosen converter is experimentally investigated for various step-up voltage ratios and for a high-power range, considering a waste heat recovery system for a maritime application. [ABSTRACT FROM AUTHOR]

This paper presents an improved H8 power converter for common-mode voltage (CMV) reduction and electromagnetic interference suppression. The proposed H8 converter can realize zero CMV variation when entering and leaving the zero state, which is mainly achieved by both the improvement of the structure and the control strategy. For the system structure, two switches are added on the dc bus to float the ac part of the three-phase converter in the zero state. Besides, additional capacitors are used to realize controllable CMV. For the control strategy, a simple control strategy is proposed for the H8 converter. It can automatically adapt to the flowing orientation of the load current to realize synchronous switching of the power switches, which effectively eliminates the impact of the dead time. Through analysis, simulations, and experiment, a comparison between the proposed H8 converter and the conventional H6 converter is performed. Results validate the effectiveness of the H8 topology. [ABSTRACT FROM AUTHOR]

Due to the zero-sequence currents in the four-wire systems, the three-phase currents become more complex on both amplitudes and phases in the unbalanced load conditions, so that the existing open-circuit (OC) fault diagnosis methods of the switching devices cannot be directly used. In this paper, an OC fault diagnosis strategy applied to four-wire T-type converter systems is proposed, which is implemented by decomposing the circuit model into a positive- and negative-sequence model and a zero-sequence model, and locating the OC fault based on the law of positive- and negative-sequence voltage error offsets and zero-sequence voltage error offsets. The proposed diagnosis method is suitable for both unbalanced load and unbalanced input voltage conditions. Meanwhile, the differences of fault-tolerant control between four-wire and three-wire systems are analyzed and compared. An effective fault tolerance strategy for inner OC faults applied to four-wire T-type converter systems is presented, which owns the ability to suppress dc bus imbalance. Simulation and experimental results are presented to verify the correctness of the proposed strategy. [ABSTRACT FROM AUTHOR]

Active pulsating power buffering (PPB) function can effectively reduce the twice-line frequency energy storage requirement in a single-phase rectifier. Existing single-phase solutions with active PPB must utilize more than two active switches in their circuits. Compared with conventional single-active-switch solutions without active PPB (e.g., a boost power-factor-correction (PFC) rectifier), the cost of additional semiconductor switches and gate drive circuitry in an active PPB-based rectifier may not be justified for low-power applications. This paper presents a family of single-switch single-phase rectifier with active PPB. Taking advantage of the on-time and off-time of a single switch, the proposed rectifiers are formulated by merging two converters that are duty and frequency controlled. The steady-state characteristics of these converters are analyzed. A step-by-step design procedure is provided, and an active control method for limiting the maximum switching frequency for wide-load-range operation is presented. A 100-W prototype is built for the demonstration of the proposed single-switch rectifier concept. It is envisaged that this concept, when combined with other circuit formulation techniques, e.g., partial power processing, dc-voltage feedback, may lead to new derivatives of single-switch rectifiers with more advanced features. [ABSTRACT FROM AUTHOR]

This paper presents a new class of switched tank converters (abbreviated as STCs) for high-efficiency high-density nonisolated dc–dc applications where large voltage step down (up) ratios are required. Distinguished from switched capacitor converters, the STCs uniquely employ LC resonant tanks to partially replace the flying capacitors for energy transfer. Full soft charging, soft switching, and minimal device voltage stresses are achieved under all operating conditions. The STCs feature very high efficiency, power density, and robustness against component nonidealities over a wide range of operating conditions. Furthermore, thanks to the full resonant operation, multiple STCs can operate in parallel with inherent droop current sharing, offering the best scalability and control simplicity. These attributes make STC a disruptive and robust technology viable for industry's high volume adoption. A novel equivalent DCX building block principle is introduced to simplify the analysis of STC. A 98.9% efficiency STC product evaluation board (4-to-1, 650 W) has been developed and demonstrated for the next-generation of 48-V bus conversion for data center servers. [ABSTRACT FROM AUTHOR]

Several applications need a high power, high output voltage ac/dc converter. The structure includes a dc/dc resonant stage, which is fed from a three-phase line. Due to standards, rectified dc input voltage varies largely from 400 to 750 V affecting the adversely overall design and current levels. In fact, losses in the inverter become unbearable if both switching frequency and transferred power are desired beyond a certain level. In those cases, it is necessary to connect several switches in parallel. As an alternative, the new switches can configure a new modular structure instead, adding more flexibility in the control to compensate input voltage variations. As a result, the required circulating current is reduced to a half, with benefits in total power losses. Moreover, the nature of the topology allows a reconfiguration of the resonant net (LCC) for low power, reducing even further the minimum circulating current under those conditions (fluoroscopy, for instance). In this paper, the new multilevel resonant topology is mathematically modeled and proposed for radiography and fluoroscopy. An example illustrates the design procedure for a given application at 100 kW, 50–150 kV. [ABSTRACT FROM AUTHOR]

The grounding of low-frequency distribution transformers is a critical concern that ensures the proper operation and protection of the distribution system. The power electronic transformer (PET), as a future alternative low-frequency distribution transformer, also needs grounding. This paper studies PET operation with arc-suppression-coil (ASC) grounding in the Y-connected medium-voltage (MV) stage, focusing on the following two aspects. [ABSTRACT FROM AUTHOR]

In this paper, a developed structure is proposed for high step-up nonisolated noncoupled inductor based multiport dc–dc converters. The voltage gain per number of devices of the proposed topology is higher than that of similar topologies. This means that, by using the same number of devices, the proposed topology can generate higher gains than other structures. In other words, the proposed topology utilizes less number of devices for producing the same voltage gain, which leads to less total cost, size, weight, and complexity. Despite high voltage gain, the normalized peak inverse voltage (NPIV) on switches/diodes is low. Higher number of input ports leads to higher gains and lower NPIVs on devices. The load energy can be absorbed and stored in first input unit. Modularity, simple structure, continuous input currents, and low input current ripple are the other profits of proposed topology. Low/medium power applications are suggested for the proposed structure. Proposed topology has been explained and operational modes along with steady-state analysis have been discussed. For better verification, the proposed topology has been compared with several multiport high gain converters. Comparison results confirm the advantages of the proposed topology. Finally, the proper performance of the proposed topology has been validated by experimental results. [ABSTRACT FROM AUTHOR]

In recent years, significant progress has been made in HVdc transmission, particularly the voltage-source-converter technology using modular multilevel converters. There is increasing demand to develop high-power dc/dc converters to interconnect HVdc systems with different voltage levels. In this paper, a novel hybrid dc/dc converter topology is proposed by the combination of a new three-switch submodule (SM) circuit and series-connected thyristors and diodes. This topology presents less amount of semiconductors, very attractive capital costs, small footprint, and low power losses. Operating principles of this new three-switch SM and the dc/dc converter are explained, while the modulation and control schemes are also developed. The validity of the proposed topology is verified by simulation results based on a 150 MW, 200 kV/300 kV dc/dc converter. Efficiency estimates indicate that this topology could have power losses as low as 0.3% rated power. A scaled-down prototype has also been built and tested to confirm its effectiveness. [ABSTRACT FROM AUTHOR]

Three-phase dual active bridge (DAB) topology is a potential alternative for high-power applications when a compact and efficient converter with a bidirectional power transfer capability is desired. In a constructed prototype, high-power SiC modules with dedicated drivers are utilized to achieve high-efficiency and compact size. Each module has two interconnected switches with anti-parallel diodes resembling a converter leg. It is observed that the driver halts the module operation as a result of protective actions such as overcurrent, gate undervoltage, or gate overvoltage. In this frozen leg mode, the module operates as a leg with two diodes until an external hardware signal resets the driver. The converter continues operation but with a reduced performance. Analysis, simulation, and verification of a three-phase DAB converter under a frozen leg operation are considered in this paper. The converter with a frozen leg has two different behaviors at light loads and heavy loads. Consequently, two different analysis methods are developed to solve converter operation in different load conditions. Results show that the power transfer capability is reduced, but this fault mode is nondestructive. [ABSTRACT FROM AUTHOR]

Novel single-phase ac–dc converters based on dual-voltage-rectifier (DV-rectifier) and voltage-sigma architecture is proposed in this paper. Dual dc-buses, i.e., a constant dc voltage bus and an adjustable dc voltage bus, are provided by the DV-rectifier. Voltages of the two dc-buses are stacked together on the output port through down-stream dc–dc transformers (DCXs). The dc output voltage is controlled by regulating the voltage of the adjustable dc-bus of the DV-rectifier. Therefore, voltage regulation is not required for the DCXs, which can always operate at their optimized operation point to ensure high efficiency. Since the voltage of the adjustable dc-bus is lower than the constant dc-bus, multi voltage-level characteristics can be obtained with the DV-rectifier, which is benefit for reduction of switching losses and improvement of conversion efficiency. In order to achieve current regulation of ac input port and voltage regulation of the two dc-buses simultaneously, multimode operation, and smooth mode transition strategies are proposed for the DV-rectifier. Operation principles, control strategies, and characteristics of the DV-rectifier and DCX-based ac–dc converter are analyzed in detail. Feasibility and effectiveness of the proposed solutions are verified with experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes a novel four-leg converter topology and the corresponding SVPWM strategy for a reluctance machine with DC-biased sinusoidal winding current. Compared with the traditional open-winding inverter topology, the number of the power devices and gate driver required for the four-leg converter topology are reduced by one-third, and the power loss is reduced. With the proposed four-leg converter, the cost of the motor drive is reduced and the power density is improved. The vector control and modulation models of the proposed four-leg converter are presented to control the winding current with both AC and DC components. With the proposed four-leg SVPWM strategy, the four-leg converter can achieve the same DC voltage utilization as an open-winding inverter. In addition to the ability to generate αβ-axis voltages, as same with conventional SVPWM, the proposed SVPWM can also generate γ-axis voltages without generating additional zero-sequence alternating voltages on the stator windings. The validity of the proposed converter and the corresponding modulation strategy has been demonstrated by simulation and experiment. The power loss and performance of the four-leg converter are compared with the traditional converter. Contrasting experiments show that the proposed topology can reduce power loss by about 15% at rated operation and achieve the same performance as open-winding inverters. [ABSTRACT FROM AUTHOR]

This paper proposes a reconfigurable dual-active-bridge (DAB) converter that is capable of switching between two converter structures for enhancing its performances at different output power levels. For 50%–100% load, the converter operates in full-bridge mode and achieves soft-switching in all switches independently of the input-to-output voltage ratio. Below 50% load, the converter is reconfigured to operate in half-bridge mode for reduced circulating current and improved light-load efficiency while maintaining the desired soft-switching characteristic of full-bridge mode. The achievement of soft-switching is aided by the use of a tuned $LCL$ resonant tank, which enables an accurate prediction of the phases of tank currents with respect to tank voltages, and therefore simplifies the realization of soft-switching. The effects of dead time are discussed and expressions for guiding the selection of appropriate dead time for ensuring soft-switching in practical implementation are derived. The proposed converter and the modulation scheme are experimentally verified with a 1.6-kW converter prototype, which demonstrates their merits in comparison with a nonreconfigurable, full-bridge DAB topology and conventional modulation schemes. [ABSTRACT FROM AUTHOR]

Fault-current handling capability of the modular multilevel converters (MMCs) under dc-cable short-circuit conditions is a major concern for the MMC applications on the high-voltage direct-current (HVDC) transmission systems, where the MMCs based on half-bridge submodules (SMs) cannot block the fault currents to protect the converter devices. In this paper, a comprehensive review for the fault-ride-through capability of the HVDC transmission systems based on the MMCs adopting different SM schemes is presented, where the MMCs can block the fault currents and compensate the reactive currents to the electric grid during the dc faults. An analysis of the dc short-circuit faults in the MMC is introduced and then the operation principle of different SM circuits building the MMC for blocking the fault currents is highlighted. The fault-tolerant operation of these MMC schemes as static synchronous compensator to enhance the ac grid stability during the dc faults is also investigated. A comparison in terms of investment cost, loss, volume, and controllability for various MMC topologies is performed. Comprehensive simulation results for the most promising topologies of the MMC with a capability of fault-ride through under dc-fault conditions are finally presented. [ABSTRACT FROM AUTHOR]

High-voltage and high-power dc–dc conversion is key to dc transmission, distribution, and generation, which requires compact and efficient dc transformers with large step ratios. This paper introduces a dc–dc converter with the input-series–output-parallel arrangement of multiple high step ratio subconverter units. Each subconverter unit is an isolated modular dc–dc converter with a stack of half-bridge cells chopping the dc down to low voltage level. The transformer provides galvanic isolation and additional step ratio. The converter achieves a large step ratio due to the combination of the series-parallel configuration, the modular cells, and the isolation transformer. The proposed dc–dc converter is analyzed in a 30 kV–1 kV, 1-MW application to discuss the operation performance, tradeoffs, power efficiency, and selection of components. Finally, the converter is validated through a laboratory downscaled prototype. [ABSTRACT FROM AUTHOR]

This paper presents a modular multilevel series/parallel converter (MMSPC) with intermodule switched-inductor power transfer. The switched-inductor voltage conversion feature allows controllable and efficient transfer of energy between modules with nonnegligible voltage difference, providing both step-down and step-up functionalities. Thus, this converter can accurately control and rapidly adjust the voltage of each module to generate an ac output voltage waveform with a controllable number of levels, increasing the quality of the output. Moreover, the intrinsic dc–dc conversion feature can generate a dc controllable output voltage and enable new applications. In this text, we specifically demonstrate how the flexibility of obtaining both ac and dc output with the same setup renders the topology promising for battery energy storage systems and dc microgrid applications. Experimental results validate the topology and concept of an MMSPC with intrinsic switched-inductor conversion. [ABSTRACT FROM AUTHOR]

This paper presents the analysis, design, and experimental validation of parameter identification of battery/supercapacitor (SC) hybrid energy storage system (HESS) for the purpose of condition monitoring and maximum power estimation. The analytic bounds on the error of battery and SC parameter identification, considering voltage measurement noise, are obtained based on the Fisher information matrix and Cramer–Rao bound analysis. The identification of different parameters requires different signal patterns to ensure high accuracy, rendering tradeoffs in the multiparameter identification process. With an appropriately designed current profile, HESS parameters are identified using recursive least squares with a forgetting factor. The identified parameters are then used to estimate the maximum power capability of the HESS. The maximum power capabilities of the battery and SC are estimated for both 1 and 30 s time horizons. The parameter identification algorithm can be applied to systems including either batteries or SCs when the optimal excitation current can be injected. Experimental validation is conducted on an HESS test-bed, which shows that the proposed algorithm is effective in estimating the HESS maximum power based on appropriate current excitation. [ABSTRACT FROM AUTHOR]

This paper proposes a family of multiport switched-capacitor multilevel inverter (SCMLI) topologies for high-frequency ac power distribution. It employs asymmetric dc voltage sources with a common ground that makes it ideal to be employed in renewable energy farms and modern electric vehicles. The proposed family of step-up SCMLI attains higher number of output voltage steps with optimum component count in comparison to several existing topologies. The problem of capacitor voltage balancing is solved as the capacitors are inherently charged to a finite voltage every half cycle. In-depth study on two staircase modulation strategies, namely, selective harmonic elimination and minimum total harmonic distortion (THD) scheme is presented with study on the variation of switching angles and THD with modulation indices under both schemes. Working principle and analysis are presented for the proposed family of topologies. Simulation outcomes are validated with experimental results under both the aforementioned modulation schemes with equal and unequal output voltage waveform steps. [ABSTRACT FROM AUTHOR]

The highly efficient and reliable inverter concept (HERIC) inverter is a cost-effective topology, which has low leakage currents and a relatively high efficiency. Thus, it is very suitable for transformerless photovoltaic systems. However, with the reported modulation methods, it is difficult to simultaneously maintain the high efficiency, good power quality, and reactive power injection of the HERIC inverter. In this paper, a hybrid unipolar pulsewidth modulation (UP-PWM) scheme is thus proposed to achieve those performances. The hybrid scheme adopts the conventional UP-PWM in the case of generating the positive power. When generating the negative power, a modulation scheme, which only requires the operation of freewheeling switches, is specifically proposed. Additionally, in the region of the output voltage and current zero-crossing points, a UP-PWM with modified deadtime is introduced. In order to validate the effectiveness of the proposed scheme, simulations and experiments are performed on a 4-kW HERIC inverter system with a 20-kHz switching frequency. The results demonstrate that the proposed hybrid UP-PWM method achieves a better performance in terms of reactive power injection than the conventional UP-PWM scheme, and a higher efficiency than the UP-PWM with deadtime. In addition, the proposed UP-PWM scheme also enables a better power quality. [ABSTRACT FROM AUTHOR]

This paper presents new space vector pulsewidth modulation (PWM) strategies for a single-phase three-level buck-boost neutral point clamped inverter coupled with impedance-source (IS) network. These strategies can be implemented for systems with any IS network with neutral point. The case study system is based on the quasi-Z-source inverter with continuous input current. To demonstrate an improved performance, the strategies are compared with a traditional PWM strategy. The advantages lie in reduced switching number, without output voltage quality distortion. The simulation and experimental results confirm the theoretical predictions. [ABSTRACT FROM AUTHOR]

This paper explores the use of the flying-capacitor multilevel (FCML) topology in high step-up conversion. Compared to the conventional two-level boost converter, the FCML topology utilizes high energy density capacitors to facilitate inductors with storing and transferring energy during the conversion process, which brings features, such as lower voltage stress on the switches, reduced voltage stress on the inductor, and high effective switching frequency at the switching node. As a result, the total volume of the passive components in the converter is greatly reduced while maintaining high efficiency at high voltage gain. To demonstrate the potential high power density and high efficiency, a hardware prototype that converts 100 V to 1 kV with 820-W maximum output power is built. Such specifications require careful optimizations in many aspects of the converter to ensure a high power density and efficiency design. The implemented solutions and associate design process are presented in detail, with comparison with other state-of-the-art solutions. The hardware prototype has successfully demonstrated a peak efficiency of 94.1%, and 329 W/in $^3$ (20 W/cm $^3$) overall power density. [ABSTRACT FROM AUTHOR]

This paper presents a drive system based on a modular multilevel converter (MMC) with high-frequency magnetic channels between adjacent-arm submodules (SMs), suitable for medium-voltage, high-power three-phase variable-speed machines. The configuration employs chains of dual half-bridge (DHB) modules linking adjacent SMs of three-phase symmetrical arms. The DHB modules are operating as power channels enabling energy exchange to restore the power imbalance among the SM capacitors. This allows arms’ ripple-powers to be entirely decoupled through bidirectional power transfer between adjacent-arm SMs, resulting in a near ripple-free SM capacitor voltage profile. Therefore, the MMC common problem of wide voltage fluctuation across SM capacitors is comprehensively solved, independent of the operating frequency. Additionally, a significant reduction in the sizing requirement of SM capacitance is achieved. The configuration is able to drive multimegawatt machines from standstill to the rated speed at the rated torque operating condition. The operating principle of the proposed MMC configuration is explained and necessary mathematical analysis is derived. Features and viability of the proposed drive system are verified through simulation and experimentation. [ABSTRACT FROM AUTHOR]

Cascaded H-bridge (CHB) inverter is the most widely used topology for a medium-voltage drive system due to the high degree of modularity, easier implementation of medium output voltage, and the ability to continuous operation under the cell fault condition. Because each power cell of CHB should have isolated dc source, multiwinding input transformer and three-phase active front end (AFE) are generally used for regenerative applications. The whole system can be simplified by replacing the three-phase AFE with single-phase AFE. However, if the control strategy of normal operation is adopted under the cell fault condition, input power imbalance among three phases inevitably occurs. In that situation, not only faulty cells, but also some unscathed cells should be excluded with giving up the maximum capability of the system, not to deteriorate grid current. This paper proposes a control scheme against the cell fault condition of the single-phase AFE CHB. By applying the proposed control scheme to the system, dc-link voltage of each cell and grid current are well regulated without imbalance even under the cell fault conditions. Finally, it can minimize the number of undamaged cells which should be turned off and maximize the capability of the system under the cell fault condition. Simulation and experimental results are provided to verify the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

Energy balancing of the alternate arm converter (AAC) is a major challenge and overlap period-based circulating current control methods are commonly used. Component parameter variation occurs due to tolerances, component aging, and internal faults leading to stored energy imbalances of modular voltage source converter (VSC) topologies. If not controlled, such variations can severely impact the operation of the AAC. Hence, component parameter variation is a key consideration for energy balancing of all sorts of modular VSC topologies, but has not been addressed in the existing literature for the AAC. This paper investigates the energy balancing capability of the AAC in high-voltage direct current (HVDC) applications under component parameter variations and proposes a compensation method to further improve its energy balancing performance. The effectiveness of the proposed method is verified in a real-time model of an AAC-HVDC transmission system from widely accepted existing CIGRE benchmark models. [ABSTRACT FROM AUTHOR]

In this paper, a nonisolated buck-boost single-inductor multiple-output (SIMO) dc–ac inverter for driving multiple independent high-frequency ac outputs of medium power is proposed. Compared with traditional bridge-type inverters, the proposed buck-boost SIMO inverter achieves 1) a smaller component count, 2) fully independent power control of its outputs, 3) better scalability in increasing the number of ac output channels, and 4) higher power efficiency. Operating in pseudo-continuous conduction mode, the rated power of each output channel of this inverter can be high while attaining zero cross regulation. The scalability factor of the proposed inverter is formally investigated and the theoretical maximum number of ac outputs is analytically derived. The targeted application of this SIMO-based inverter is for driving multiple transmitter coils to realize versatile multidevice medium-power wireless power transfer. A hardware prototype of a single-inductor three-output buck-boost inverter delivering a medium power of 8.4 W per output channel has been constructed. It is experimentally verified that precise and independent current regulation of individual transmitter coil is achievable with the proposed inverter. [ABSTRACT FROM AUTHOR]

The paper presents a new transformerless single-phase single-stage buck–boost grid-connected voltage source inverter (VSI) topology. The topology can achieve efficient power conversion with a wide input voltage range, number of magnetic devices reduction and low leakage current. The proposed VSI topology consists of high frequency semiconductors for shaping inductor currents, and low frequency semiconductors to form grid CL filter structure for different conditions. This CL filter uses the same buck–boost inductor, thus no additional line frequency inductor is required. Besides, common mode voltage, a main problem of transformerless grid-connected VSI, is mitigated, since the capacitor in the CL filter clamps the voltage between the grid and the bus terminal. The performance of the proposed VSI is experimentally verified. The results show that the proposed VSI guarantees sinusoidal output current and wide input voltage range, and has a good agreement with the theoretical findings. [ABSTRACT FROM AUTHOR]

This paper presents three nonisolated high voltage gain dc–dc converters with ripple-free input current. The proposed converters combine coupled inductors and voltage-doubler structure (VDS) to achieve high step-up of input voltage. An active clamp circuit is used to suppress voltage spike of the switch caused by of the leakage inductor of the coupled inductor. VDS is placed in the secondary winding of the coupled inductor that clamps the diodes voltage stress. Working principle and design methodology of the proposed converters are presented in detail. Experimental results for a 300 W laboratory prototype, 48 V input voltage, and regulated output voltage of 400 V, are shown to validate the operation of proposed converters. [ABSTRACT FROM AUTHOR]

This paper proposes a novel unified expandable low switch power electronic converter architecture for grid integration of direct drive variable speed wind turbine (VSWT) system using permanent magnet synchronous generator (PMSG). The proposed unified expandable power converter can interface two or more bidirectional output ports, such as wind generators, energy storages, and grid. The size of the power converter is compact because of fewer number of power electronic switches and protection devices, and its architecture is easily expandable to accommodate more outputs, i.e., in this case, the wind turbines. A generalized sequential space-vector modulation technique is developed based on the operational principle of the proposed converter to control the outputs autonomously in order to track the maximum power point for individual VSWTs-driven PMSGs. It is expected that the proposed approach will reduce the cost of power electronic converters in a wind farm, compared to both ac- and dc-link-based topologies, which are available for the moment. [ABSTRACT FROM AUTHOR]

This paper proposes an enhanced hybrid modular multilevel converter (MMC), which utilizes a combination of half-bridge submodules (HBSM) and at least one full-bridge submodule (FBSM). In the proposed structure, FBSMs work with half of the HBSMs nominal voltage in each arm. Due to the presence of FBSMs, HBSMs switching frequency drops significantly, which reduces the converter power loss compared to half-bridge based MMCs. Furthermore, because of redundant FBSMs, (2N + 1)-modulation can be employed to generate the output voltage without increasing the circulating current, thus, the converter performance is improved notably. Besides, with the redundant FBSMs, the converter can continue its operation even if a fault occurs in one of HBSM switches. All the control procedure is accomplished using model predictive control strategy and performance of the proposed converter is verified by several simulation and experimental studies. The obtained results confirm the feasibility of the proposed scheme in reducing the converter loss, improving its performance and fault-tolerant operation. [ABSTRACT FROM AUTHOR]

The central inverter topology based on three-level converters is widely used in large-scale photovoltaic (PV) power plants because of its simple and reliable structure and high efficiency. However, when two PV arrays are connected in series for higher dc-link voltage, the single maximum power point tracking (MPPT) operation cannot function properly when there is partial shading between the arrays. This paper presents a configuration where the two PV arrays are connected in series together with an auxiliary power converter feeding a neutral-point-clamped central inverter. This configuration ensures maximum power production from both PV arrays during partial shading conditions, achieving the MPPT operation for both PV arrays. The proposed converter together with their controls are verified by simulation and experiment. [ABSTRACT FROM AUTHOR]

LEDs have finally emerged as the dominant lighting technology. As such, the lighting industry values power converters that have high efficiency, unity power factor, minimal flicker, dimming, low cost, and a small form factor. This paper presents an integrated circuit (IC) LED driver that is designed to achieve these goals. It introduces multilevel converters with sigma–delta modulation to the power IC space. The driver features a pair of sigma–delta-controlled multilevel converters. The first is a multilevel rectifier responsible for power factor correction and dimming. The second is a bidirectional multilevel inverter used to cancel ac power ripple from the dc bus. The system also contains an output stage that powers the LEDs with dc and provides for galvanic isolation. The IC LED driver has been simulated and prototyped on a silicon fabrication process. Its functional performance indicates that integrated multilevel converters are a viable topology for lighting or other similar applications. [ABSTRACT FROM AUTHOR]

Multileg Class-D amplifiers (CDAs) with phase-shifted carrier modulation can increase the equivalent switching frequency and reduce the output current ripples, which further reduces the size of the output filter. However, these benefits are degraded by the tolerances in the phase inductance values. The phase inductance mismatches impact the ripple cancelation effects (the harmonic contents at switching frequency and its harmonics appearing in the output current ripple). Therefore, the quality of the output waveform can further be impacted. Current research works dealing with this issue mainly focused on the interleaved dc–dc converters, which does not cover the analysis in multileg CDAs or inverters, especially for the full-bridge configuration. This paper proposes a general analytical method to characterize the steady-state phase and the total current ripple in the multileg CDAs with full-bridge configuration under inductance mismatches. Monte Carlo simulation is used to study the impact of inductance mismatches on the harmonic contents of the total current ripple, and the distribution law of the inductances at the worst case is revealed. The analytical method is verified by simulation and experimental results of a four-leg full-bridge CDA. A design guideline is given to optimize the filter design based on the analytical method. [ABSTRACT FROM AUTHOR]

In this paper, a grid-tied residential smart microgrid topology is proposed, which integrates energies of a photo-voltaic (PV), a fuel cell, and a battery bank to supply the local loads through a combination of electric and magnetic buses. In contrast to multiple-converter-based microgrids with a common electric bus, using a multiport converter with a common magnetic bus can effectively reduce the number of voltage conversion stages, size, and cost of the renewable energy system and isolates the conversion ports. The resultant topology utilizes a centralized system level control that leads to a faster and more flexible energy management. The proposed microgrid is able to operate in multiple grid-connected and off-grid operation modes. A fuzzy controlled energy management unit (EMU) is designed to select the appropriate operation mode considering both real-time and long-term predicted data of the energy generation and consumption. A mode transition process is designed to smooth the mode variation by using a state transition diagram and bridging modes. To improve the microgrid operation performance, appropriate control techniques, such as synchronized bus-voltage balance, are used. A prototype of the proposed microgrid and the EMU are developed and experimentally tested for three different energy management scenarios. Energy distribution and energy cost analysis are performed for each scenario to validate the proposed control method. [ABSTRACT FROM AUTHOR]

The capability of misalignment tolerance is vital for an inductive power transfer system. This paper proposes a novel unsymmetrical coupling structure that can remarkably enhance the output voltage stability with respect to the horizontal, vertical, and angular displacements. The core of this structure is concentrated magnetic field. The optimization method to derive the optimal loosely coupled transformer providing the strongest tolerance to misalignment and fulfilling the requirement of the minimum coupling coefficient is presented. The proposed structure is compared with planar circular and square coils and double-D (DD) coupler from the perspectives of magnetic coupling and anti-misalignment capability. A 200-W prototype is finally fabricated, where the primary series, secondary series-parallel compensation topology is employed to further improve the system's tolerance to misalignment. A maximum output voltage ripple factor of 2.83% and a minimum system efficiency of 91.9% are achieved when the horizontal displacement is as high as one-third of the coupling coil. [ABSTRACT FROM AUTHOR]

Applications such as renewable energy generation, electric vehicles, and low-power UPS require single-phase ac/dc conversion. However, this conversion introduces a considerable amount of second-harmonic ripple on the dc link. If not filtered, this distortion hinders the converter's performance as well as the energy quality on both the ac and dc side. To mitigate this problem, a large electrolytic capacitor is usually the solution of choice, which mitigates the voltage ripple, but has drawbacks of its own, including the increased size and cost associated with the large capacitance and the limited lifespan of electrolytic capacitors. Alternative solutions to the problem include integration of an active filter circuit to the converter, which can utilize a storage element with the objective of mitigating power ripple. Such solutions have often been proposed alongside a control system, which is either highly complex or relies on open-loop feedforward techniques. This paper presents a control system, which adapts the single-input space vector concept for a single-phase application and leverages its simplicity and closed-loop architecture, allowing the controller to perform well in the presence of disturbances and parameter uncertainty. Experimental results are provided to elucidate the controller's performance on a single-phase grid-connected photovoltaic array application. [ABSTRACT FROM AUTHOR]

This paper presents a novel step-up dc to ac converter with only one power supply. These types of converters are suitable for renewable and sustainable energy applications with low input dc sources. The proposed topology has the ability of self-voltage balancing and does not apply end side H-bridge to produce a bipolar staircase waveform. Consequently, switching losses and voltage stress of semiconductor components are reduced to a great extent. A small dc voltage source can be used to achieve a high voltage high quality ac waveform through switching the precharged capacitors in series and in parallel. Circuit configuration and its operation principle, capacitors’ charging process, thermal model, capacitances, and losses calculations are discussed in details. Moreover, the comparison of the proposed circuit with the other single source multilevel converters shows that the proposed topology reduces the number of circuit elements. Finally, a laboratory nine-level prototype is built to verify the theoretical analyses and feasibility of the proposed topology. The experimental results show that the converter efficiency at 1 KW output power is 92.75%. [ABSTRACT FROM AUTHOR]

A fast modularized multiwinding transformer balancing topology (MMTBT) for series-connected supercapacitors is proposed in this paper. With the proposed MMTBT, the voltage balancing inside modules and between modules are completely decoupled and the degree of modularization is high. This is different from the existing MMTBT, with the existing MMTBT, different modules share the same PWM drive. While with the proposed MMTBT, different modules can be driven by different PWM, then the variable frequency control strategy can be used to realize a fast balancing speed. With the proposed variable frequency control strategy, the average balancing current will be large and the balancing speed inside modules will be fast. With the proposed MMTBT, the balancing between modules is realized by discharging the higher voltage modules. The MMTBT of the higher voltage modules will act as a fly-back converter and the excitation current is in continuous current mode (CCM) to realize a great discharging power. First, the extra energy from the higher voltage module is transferred to the filter capacitor of the half-bridge converter. Then, the outputs of the half-bridge converters are connected in series to form a multilevel converter to act as the input of a boost converter. At last, the energy is transferred back to the supercapacitor energy storage system by the boost converter. The higher voltage module will be discharged with a great discharging power, then the balancing speed between modules will be fast. The fast balancing speed is realized inside modules and between modules, then the balancing speed of the whole system will be fast. The variable frequency control strategy and the control strategy of boost converter are analyzed in detail and the fast balancing speed of the proposed balancing topology is proved by experimental results. [ABSTRACT FROM AUTHOR]

High-brightness light-emitting diode (LED) is next generation of green lighting. However, the bulky electrolytic capacitor is required to compensate the difference of pulsating power, thereby restricting the lifetime. Meanwhile, the existing drivers based on pulse frequency modulation (PFM) is bound to arouse heavy electromagnetic interference. In this paper, the series resonant converter based LED drive is proposed to overcome the shortcomings of electrolytic capacitor and PFM control. The proposed method is to attenuate the low frequency ripples delivered from the power factor correction (PFC) to LEDs; therefore, the capacitance is reduced for energy storage of offline LED drivers. On account of the adoption of the switching controlled capacitor (SCC), the constant frequency control is achieved by the regulations of the equivalent capacitance. Half-bridge switches are shared by the bridgeless PFC and the resonant unit, therefore, single-stage LED drive is realized with high efficiency. In addition, SCC is simultaneously shared for the upper and lower half-bridge to reduce the cost and improve the power density. Operating principle, design considerations, and performance comparisons are examined in detail. Finally, all the superior performances of proposed LED driver are verified by simulation and experimental prototypes with two-channel LEDs, and rated output power of 80 W. [ABSTRACT FROM AUTHOR]

Thanks to the advantages of high fuel efficiency and low emission, more electric aircraft (MEA) has attracted increasing attention in recent years. For MEA, high reliable power converters which can keep working after multiple unexpected faults, are highly desired in the electrical power system to guarantee safety. In order to fulfill the high reliability requirements, a novel fault-tolerant LLC converter is proposed for MEA in this paper, which can keep working after two ideal shorted-circuit faults occurred on switches with a redundant circuit and topology reconfiguration. The redundant circuit is employed to achieve the first fault-tolerant ability, and when the second switch failure occurs, the proposed converter would be auto-reconstructed with the aid of two additional diodes to ensure uninterrupted operation. Because only two extra diodes are added to achieve the second fault-tolerance, the system reliability is significantly enhanced with low additional cost. Moreover, both the voltage/current stresses and the small-signal models of proposed converter are approximate in all prefault and postfault modes, contributing to simplified circuit design and reliable control system. Finally, a 500 W prototype is designed and built to experimentally verify the advantages of proposed fault-tolerant LLC converter. [ABSTRACT FROM AUTHOR]