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Incorporating AC-type flying capacitors (FC) between series-connected devices is an effective way to enhance the rated voltage for high-power applications based on current source converters (CSCs). Through appropriate modulation and FC voltage control, it is possible to achieve improved DC bus voltage quality with reduced common-mode voltage (CMV) and low dv/dt. On the other hand, the parallel CSC is a popular choice for increasing the system's rated current to accommodate higher power applications. The use of interleaved modulation techniques can improve the harmonic performance of parallel converters while reducing the need for passive filters. The modular flying capacitor clamped (FCC)-CSC structure can combine these advantages, achieving higher rated power along with improved power quality on both the DC and AC sides. Moreover, the enhanced AC quality contributes to the regulation of FC voltage and further improves the DC-side voltage quality. This paper analyzes the operation principle of the parallel FCC-CSC structure and proposes an interleaved space vector modulation (SVM) method to enhance the harmonic performance of the AC output. Additionally, an optimized zero-state replacement (ZSR) based FC voltage control and a DC-link current balance strategy built on this control are introduced. Simulation and experimental results validate the effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]

To extend the lifetime, improve the power density and reduce the system cost, the film capacitor is applied to replace the large-volume electrolytic capacitor in motor drives. As the dc-link voltage fluctuates periodically, the rotor position estimation error and operation stability are necessary to be concerned in the position sensorless control methods. A cross-decoupling complex filtering-based position estimation method is investigated for the reduced capacitance interior permanent magnet synchronous motor drive system. Harmonic components of the extended back electromotive force (EEMF) caused by the dc-link voltage fluctuation are analyzed to evaluate the additional rotor position error. A cross-decoupling complex filter realized by the multiple first-order complex filters with different center frequencies is designed to improve the position estimation precision. Harmonics of the EEMF are suppressed and the position error can be eliminated. The estimation precision and operation ability are improved. Experimental results are performed to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Sharp LC resonance peak may enlarge inherent harmonics, dominant harmonics of the supply voltage generated by a three-phase diode rectifier, around the resonance frequency, which will intensify fluctuations of the dc-link voltage, and grid currents in motor drives with small dc-link capacitor. In this article, a novel resonance suppression strategy based on inherent harmonics impedance shaping is proposed specially for three-phase input permanent magnet synchronous motor (PMSM) drives with small dc-link capacitor. Instead of increasing the damping of the whole system for resonance suppression, the motor side power disturbance can be reduced by designing the impedance for inherent harmonics around LC resonance frequency based on the new model with the consideration of motor side characteristic. For damping current generation, the angle of the virtual admittance is modified to eliminate the influence of the dc-link voltage sampling delay. Experimental results show the effectiveness of the method on a prototype of electrolytic capacitorless PMSM drive. [ABSTRACT FROM AUTHOR]

Electrolytic capacitorless Vienna rectifiers have many advantages, such as longer lifetime and higher power density. However, the reduced dc-link capacitance aggravates the voltage stress due to the neutral point (NP) fluctuation. In this article, a hybrid modulation strategy combining the modulations of redundant vector and compression vector is proposed, which can realize the NP voltage balance for electrolytic capacitorless Vienna rectifiers. On the basis of analyzing the limitation of NP-balance capability of conventional space vector pulsewidth modulation (PWM) strategy in the region of high modulation index, the negative influence of reduced capacitance on the NP fluctuation and the input current harmonics is revealed. To suppress the NP fluctuation, the compression coefficient is introduced to redistribute the duty cycles of voltage vector, which can reduce the negative effect of medium vector on the NP voltage. In addition, the phase voltage error is modeled to reduce the input current harmonics with the appropriate adjustment factor. The implementation of the proposed strategy is realized by the equivalent carrier-based PWM, which can avoid the sector judgment and angle calculation. By using the proposed strategy, the NP voltage balance and the input current harmonics reduction can be realized simultaneously. The effectiveness of the proposed strategy is verified on an electrolytic capacitorless Vienna rectifier platform. [ABSTRACT FROM AUTHOR]

A 1 MHz active-clamp flyback converter for solar street-lighting applications, featuring a partial power processing, is proposed in this article. The secondary-side resonance between the output capacitor and transformer leakage inductor is utilized to reduce rms current and conduction losses. In comparison with the traditional light-emitting diode drivers based on full power converters (FPCs), the proposed approach that uses partial power converters (PPCs) can significantly improve the overall system efficiency by eliminating the redundant power handling process. The universal schemes are discussed and the optimal solution is eventually determined by the partial power ratio. The advantages of PPC compared with FPC in device stress, losses, and regulation capability are demonstrated by simulation. With GaN devices, a 100 W/1 MHz prototype was built to verify the analysis. The experimental results show that the proposed topology can reduce the power rating of the converter by up to about 80% while increasing the system efficiency by up to 95.8%. [ABSTRACT FROM AUTHOR]

This letter proposes a switched capacitor (SC)-based continuously adjustable modular bidirectional dc–dc converter. The structure of the proposed converter consists of three types of modules, series–parallel SC converter module, regulating module, and resonant SC converters module. A basic configuration of three modules working in buck operating mode is analyzed in detail. The boost mode operation is symmetrical to the buck mode. The regulation module provides all regulation capability, and the other two modules operate at fixed duty cycle and provide the main conversion ratio. A prototype of the basic configuration was built to verify the theory. The peak efficiency of the prototype is 97.15%. [ABSTRACT FROM AUTHOR]

In meshed high-voltage direct current (HVdc) grid, the current flows through the lines cannot be controlled with sufficient freedom without additional power electronics-based devices, namely current flow controller (CFC). In this article, a novel hybrid modular interline CFC is proposed based on H-bridge submodules and thyristor valves. Due to its modularity, the proposed CFC is particularly suitable for applications requiring high voltage and large power capacity. The circuit structure, operation principle, and parameter design are presented. In addition, a control strategy is developed for the proposed CFC. Simulations are carried out using a four-terminal meshed HVdc grid to verify the effectiveness of the topology and its control strategy. A downscaled prototype is built, which further validates the proposed CFC. [ABSTRACT FROM AUTHOR]

In this article, a high-performance modified Y-source dc–dc converter is proposed. Comparing with traditional Y-source dc–dc converter, the proposed converter can achieve soft switching characteristics. Due to the discontinuous conduction mode operation of one of the coupled inductor windings and the resonant cell constructed by switch parasitic capacitor, the switch can operate in zero voltage switching (ZVS) and diodes realize zero current switching. Also, the voltage gain of the proposed converter is greatly improved. Meanwhile, the control strategy of hybrid pulsewidth modulation and PFM is adopted to guarantee the ZVS operation within a wide range. A 160 W experimental prototype based on planar coupled inductor is built to verify theoretical analysis and efficiency is up to 94.45% under full load condition. [ABSTRACT FROM AUTHOR]

Inthis article, a two-phase series capacitor dual-path hybrid dc–dc converter with the step-down ratio of less than 1/6 is proposed for the first time. In this converter, the output current is divided into capacitance- and inductance-path, so the average value and ripple of inductance current are reduced. On the same time, the conduction loss caused by inductance equivalent series resistance (ESR) is also reduced. The addition of series capacitor leads to desirable characteristics, including lower switching stress, switching loss, parasitic output capacitance loss on mosfet, automatic phase current balancing, duty ratio extension, etc. A 120 W prototype has been designed to demonstrate theoretical analysis. Obtained efficiency was up to 93.18% at full load. Experimental results show good agreement with theoretical analysis and high feasibility of proposed converters. [ABSTRACT FROM AUTHOR]

Wireless power transmission technology is used to transmit energy without contact in the field of electric vehicles, consumer electronics, and other industries. Among them, there are some applications with very low coupling coefficient where multilayer coil needs to be wound. Influenced by the parasitic capacitor between layers, the loss of the multilayer coil increases. The improved coil winding method and compensation method are proposed in this letter. Winding coils following the same sequence from outside to inside in each layer and connecting capacitors in series between layers of the coil can significantly reduce the voltage of the layers’ parasitic capacitor, which will decrease the coil loss. Compared with traditional method, the improved method increases the system efficiency at heavy load and light load by 0.74% and 2.48%, respectively. A 1-kW prototype was built with the maximum efficiency of 93.58%. [ABSTRACT FROM AUTHOR]

Beat phenomenon is an important issue for the practical application of electrolytic capacitorless motor drives. In this study, the characteristics of stator current harmonics caused by the voltage sampling delay are analyzed. Further, the beat phenomenon generated from the interaction between the harmonics and the fundamental currents is investigated, and the envelope feature of the stator current is derived mathematically. For the purpose of suppressing the beat phenomenon, a voltage reconstruction strategy is proposed to reduce the influence of dc-link voltage sampling delay at the six times of grid frequency. By utilizing the reconstructed dc-link voltage for calculation of PWM duty ratio, the beat phenomenon can be attenuated significantly. The proposed method can be integrated into motor control system easily. Experimental results show the effectiveness of the proposed strategy in a prototype of electrolytic capacitorless permanent magnet synchronous motor drive. [ABSTRACT FROM AUTHOR]

Modular multilevel converter (MMC) is regarded as an emerging topology in medium-voltage (MV) variable-speed motor drive applications, particularly for driving fan-/pump-like loads. The main challenge is the large capacitor voltage ripple of MMC at low speed with high starting torque. In this brief, a simple and cost-effective modified MMC topology is introduced, which can provide high toque to motor during the zero/low frequency. The topology is particularly suitable for fan-/pump-like loads. Circuit structure and operation principle of this modified topology is explained, and the control schemes are also developed. Validity and effectiveness of this topology are verified by experimental results. [ABSTRACT FROM AUTHOR]

Medium-voltage (MV) dc collection system is a promising solution for future integration of large-scale renewables at remote places. This requires a high-power dc–dc converter to step up the voltage and connect with the high voltage direct current transmission line. In this article, a novel modular high-power dc–dc converter is proposed, with the combination of half-bridge and full-bridge submodules (SMs), as well as thyristors and diodes. It alternatively configures the SMs into parallel connection with the MV side to effectively share high current stress while series connection with the high voltage side to share the high voltage stress. It presents attractive features such as high device utilization rate, low cost, high step-up ratio, high efficiency, and small footprint. The circuit structure, operation principle, and the control schemes are discussed. Simulation results demonstrate the effectiveness, and the experimental results from a scaled down prototype further prove the proposed concept. [ABSTRACT FROM AUTHOR]

In this article, a soft-switching transformer-less step-down converter based on a resonant current balance module is proposed. An LED driver is taken as an example of the analysis and design of the converter. The converter is made up of a stacked half-bridge, resonant current balance modules, and pairs of light-emitting diode (LED) strings. The resonant current balance modules allow the proposed converter to realize automatic current sharing, soft switching, and extending to a 1/N converter. The proposed converter can operate in discontinuous conduction mode (DCM) or continuous conduction mode (CCM) mode by choosing different operation frequencies, and achieve zero current switching or zero voltage switching (ZVS), respectively. Also, by using frequency doubling technique in the half-bridge, the switching losses are reduced by half under the same conditions. A 15.8-W experimental prototype with 100 V input voltage and 25 V output voltage has been implemented in the laboratory, verifying the feasibility of the soft-switching transformer-less step-down converter. [ABSTRACT FROM AUTHOR]

This article presents a dc solid state transformer based on three-level power module (PM) (TL-DCSST) for interconnection of medium-voltage dc (MVdc) and low-voltage dc distribution system. The proposed TL-DCSST adopts the low-voltage insulated-gate bipolar transistor (IGBTs) with excellent switching characteristics to build medium voltage PM and reduces the number of medium frequency transformer (MFT). This topology features inherent antibias mechanism for MFTs on the primary side, which saves the resonant capacitor at primary side. Meanwhile, the active front end is integrated to realize voltage and power regulation, low voltage ride-through and DC fault handling for MVdc side. In this article, the topology, operation principle, interleaving modulation, circuit parameter design, and control schemes are presented and analyzed comprehensively. At last, a prototype rated at 7 kW has been built and tested, and the experimental results verify effectiveness of the proposed TL-DCSST. [ABSTRACT FROM AUTHOR]

With the rapid development of voltage source converter-based high-voltage direct current (HVdc) transmission, it is an irresistible trend that HVdc grid will come into being. High-voltage and high-power dc/dc converters will serve as dc transformers in HVdc grid to interconnect dc lines with different voltage ratings. This article proposes a monopolar symmetrical dc/dc converter which is composed of cascaded half-bridge submodules and series-connected insulated-gate bipolar transistors. This hybrid topology features low capital costs, high efficiency, small footprint, and bidirectional power transfer capability. Operation principle, parameter design, and the control strategies of this topology are introduced. A 480-MW, ±500 kV/±160 kV monopolar symmetrical dc/dc converter is simulated to verify its performance and evaluate the efficiency. In addition, a downscaled prototype rated at 2.4 kW, ±300 V/±100 V has been built and tested. Experimental results further validate the effectiveness of the proposed dc/dc converter. [ABSTRACT FROM AUTHOR]

Harmonic state space (HSS) is seen as an effective impedance modeling method to precisely characterize the internal harmonic features of the modular multilevel converter (MMC). However, the existing MMC impedance models assume the ideal grid, ignoring the grid impedance, and they also do not incorporate the widely used dual-loop control and phase-locked loop (PLL). In this article, a complete MMC impedance model based on HSS is proposed to reveal the grid impedance coupling effect of MMC. The model analysis results demonstrate that the MMC impedance is coupled with the grid impedance due to the internal harmonics. This coupling causes MMC to be affected by the grid impedance and may cause instability. On the other hand, the proposed model not only consists of the ac current and the circulating current control, but also incorporates dc voltage outer loop and PLL with a clear physical meaning. Based on the proposed model, this article illustrates the factors that will enhance the coupling, which shows that the proposed model has to be used to improve the accuracy of the analysis. Finally, effectiveness of the proposed model is verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

In this article, an ac/dc converter based on the stacked boost circuit and dual-mode LLC circuit is proposed. In the power factor correction (PFC) part, two boost circuits are stacked to halve the input voltage and the inductor can be shared. The stacked boost circuit can achieve PFC and soft-switching characteristics with open-loop control with the complementary driving signal. In the dc/dc part, a dual-mode LLC circuit is adopted based on two stacked half-bridge structure. The proposed ac/dc converter can be utilized in wide input voltage variation conditions. A prototype is proposed in the laboratory and the experimental results verify the feasibility of the proposed converter. [ABSTRACT FROM AUTHOR]

This article proposed a novel scheme integrating full-duplex communication into high-power wireless power transfer systems. The power and data are transferred through the same inductive link. A pair of coupling coils with taps are employed to omit the trap inductors that are widely employed in former simultaneous wireless power and data transfer (SWPDT) systems. The proposed scheme can reduce the system cost and size and improve the power transfer efficiency. The power and bidirectional data are transmitted using carriers of different frequencies. Frequency division multiplexing technique is utilized for full-duplex communication. The duplexer is carefully designed to separate the transmitted and received data signals. The circuit model of the system is built to analyze the power and data transfer performance. The crosstalk between the power and data transfer is also discussed. To improve the performance of data transfer, the method to determine the optimal coil tap position is proposed. A 300-W SWPDT prototype with a full-duplex data rate of 500 kb/s was built to demonstrate the feasibility of the proposed system. [ABSTRACT FROM AUTHOR]

A novel discontinuous conduction mode (DCM) soft-switched single ended primary inductor converter (SEPIC)-based high-frequency converter is presented in this article with the advantages of high voltage gain and low voltage stress. In order to achieve higher voltage gain, it integrates a switched inductor with a coupled inductor–based modified SEPIC converter, and a resonant cell is built with integration of a resonant capacitor, which enables the switches to work under zero voltage switching (ZVS). Therefore, the working principle is changed and better performance is obtained. The proposed converter can operate in both continuous conduction mode (CCM) and DCM, but ZVS can only be achieved in the discontinuous mode; hence, DCM is more suitable for high-frequency applications. Mode analysis, parameter design, and boundary of the two working modes are all presented in detail. For higher efficiency, a 500-kHz/54-W DCM prototype with 15 voltage gain has been designed to demonstrate theoretical analysis. Obtained efficiency was up to 93.4% at full load. Experimental results show good accordance with theoretical analysis. [ABSTRACT FROM AUTHOR]

Three-phase input diode rectifier interior permanent magnet synchronous motor (IPMSM) drives with small-volume film capacitors have many merits, such as high reliability, high power density, and low cost. However, in regenerative braking mode, the dc link may suffer from overvoltage due to the application of slim film capacitors. In this paper, a novel antiovervoltage strategy is proposed by controlling the motor voltage using stator current vector orientation. The relationship among the braking torque, the dc-link capacitance, and the antiovervoltage ability is analyzed quantitatively. Based on the analysis of principle, a closed-loop antiovervoltage regulation scheme is presented, which is easy for applications. Additionally, this method has the merit of low motor parameter dependence. Meanwhile, the small signal model of the electrolytic capacitorless IPMSM drive is derived for the coefficient design of the voltage controller. The proposed algorithm is finally implemented on a 2.2-kW electrolytic capacitorless IPMSM drive platform to verify the effectiveness of the antiovervoltage control scheme. [ABSTRACT FROM AUTHOR]

Recently, remarkable progress has been made in the voltage-source-converter-based high-voltage direct current (HVdc) transmissions. For the upcoming need to interconnect multiple dc transmission lines with different voltage levels, high-voltage and large power dc/dc converters are necessary. This article investigates a nonisolated bidirectional dc/dc converter that is composed by cascaded half-bridge submodules, series-connected diodes, and mechanical disconnectors. This hybrid topology presents very attractive features, such as low cost, high efficiency, and light weight. Operation principle, parameter design, and dedicated control strategies are developed. Simulation of a 150-MW, 200 kV/300 kV dc/dc converter has been performed to verify its performance and evaluate the efficiency. Moreover, a downscaled three-phase prototype rated at 500 V/300 V 4.5 kW has been built and tested. The experimental results further confirm the effectiveness of the proposed dc/dc converter. [ABSTRACT FROM AUTHOR]

Electrolytic capacitorless vector-controlled interior permanent-magnet synchronous motor (IPMSM) drives have many advantages, such as higher reliability, longer lifetime, and lower cost. However, the dc-link may suffer from the overvoltage during motor transient process due to the use of slim film capacitors in the diode rectifier front end. The conventional antiovervoltage method by controlling the quadrature axis current will lead to energy control error, which causes large dc-link voltage control error. In this paper, a novel antiovervoltage control scheme with coefficient autoregulation is proposed based on the concept of system loss. A dual antiovervoltage controller is designed to enhance the voltage control performance by controlling both the direct and quadrature axis currents to achieve more effective active braking. The coefficients of the dc-link voltage controller are autoregulated to maintain the enough stability margin during the regenerative braking. By using the proposed method, the dc-link overvoltage phenomenon can be avoided while guaranteeing the maximum copper loss during the braking process. The proposed algorithm is ultimately verified on an electrolytic capacitorless IPMSM drive. [ABSTRACT FROM AUTHOR]

This paper proposes a 20 MHz low-profile dc–dc converter with magnetic-free characteristics based on aircore planar inductors. The switch and diode of the proposed converter operate in soft-switching modes, which significantly reduces the switching loss. Furthermore, the parasitic capacitances are taken as part of corresponding resonant capacitors. A high-performance aircore inductor with a variable width and an optimal connecting angle is analyzed. The optimal parameters design method to achieve minimum winding resistance is derived in detail. The resonant driving method is adopted to reduce driving loss in a high-frequency condition. A 20 MHz prototype is built to verify the feasibility of the proposed converter. [ABSTRACT FROM AUTHOR]

In this paper, many impedance-source inverters with coupled inductors have been investigated to obtain a high step-up boost ratio. However, the leakage inductors in these topologies induce great voltage spikes at the dc link, which will increase the voltage stress of switches. Thus, the power level of inverters is limited. Furthermore, the efficiency of the inverters can be degraded by the losses associated with leakage inductors. To address abovementioned issues, this paper proposes a family of low-spike high-efficiency Y-source inverters. The proposed inverters have the ability of eliminating voltage spikes at the dc link and recycling the leakage energy via the additional diode and capacitor. In order to show the excellent characteristics of the proposed topologies, this paper compares the performances of the proposed inverters and the improved-Y-source inverter in many aspects. Simulation and experimental results have verified the abilities of the proposed inverters. [ABSTRACT FROM AUTHOR]

With the increase in demand for high voltage gain characteristics, traditional Boost circuit is no longer suitable because of the extreme duty ratio. In this brief, with the integration of two diodes, three capacitors, and a transformer, a 1 MHz transformer-based modified SEPIC circuit is presented. Planer magnetic components are adopted, and therefore the core volume does not increase. Higher voltage gain and lower voltage stress are obtained simultaneously. Moreover, zero voltage switching is achieved at the same time, which reduces the switching loss caused by the increment of switching frequency. The operational principle and parameter design process are introduced in detail. An 80 W prototype is designed to demonstrate theoretical analysis. Obtained efficiency was up to 92.6% at full load. [ABSTRACT FROM AUTHOR]

With the rapid development of photovoltaic and fuel cell stacks, high voltage gain converters are urgently demanded. Conventional boost is limited by the exaggerated duty cycle, it is impossible to obtain a high voltage gain while ensuring efficiency. Therefore, a zero-voltage switching (ZVS)-modified SEPIC converter that combines a voltage multiplier cell with traditional SEPIC is proposed in this paper. With detailed parameters design process, this presented converter works at zero voltage switching (ZVS), while obtaining high voltage gain without extremely high duty cycle. Besides, voltage stress is also reduced and low-voltage component with lower parasitic parameters can be used, thus efficiency is maintained. In order to further improve the power density, an integrated inductor scheme is adopted in this paper without changing intrinsic working states of the two inductors. A 36-W prototype is built, and experiments are conducted to verify the advantages of the proposed converter. The efficiency is up to 91.5% at full load. [ABSTRACT FROM AUTHOR]

This paper presents a novel integrated-stage light-emitting diode (LED) driver based on Flyback and resonant converters. The Flyback converter realizes power factor correction in the discontinuous conduction mode. The resonant converter is operated as a dc–dc converter to support the LED loads. Moreover, the resonant converter can clearly decrease the drain–source voltage of the active switch and exhibits zero-voltage-switch characteristics. Therefore, a cost-effective MOSFET can be chosen as the main control component that can decrease the cost of the whole system. Compared to a single-active-switch converter (such as Class-E converter), the number of passive components in the resonant converter can be limited to four. Therefore, the power density of the system can be improved drastically. In this paper, a 100-W prototype is presented under the experimental condition to validate the proposed integrated-stage LED driver. [ABSTRACT FROM AUTHOR]

Beat phenomenon is an important concern in the reduced dc-link capacitance motor drive system. In previous research works, the topic is mainly concentrated on the beat phenomenon caused by the interaction of the fluctuated dc-link voltage and the motor phase voltage. In this paper, another form of the beat phenomenon generated by the fluctuated dc-link voltage and the severely fluctuated load torque is investigated. The effect of the beat phenomenon on the grid current and the motor speed is analyzed, which fluctuate with the low-frequency oscillation. In order to improve the drive system performance, a power balancing controller is proposed to suppress the grid current fluctuation, and a resonant controller is utilized to regulate the periodic power signals. Meanwhile, the applied fluctuated torque suppression method could improve the performance of the motor speed, which is only sensitive to the frequency of the fluctuated load torque. Experimental results are provided to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

A high-frequency high voltage gain discontinuous conduction mode coupled-inductor boost LED driver based on planar component is presented in this paper. GaN switch is adopted with lower conducting resistance and higher switching speed. Zero voltage switching (ZVS) is achieved at the same time to reduce high switching loss caused by high switching frequency. Compared with the previous work, the voltage gain is higher and efficiency is higher because of ZVS. This paper focuses on high efficiency; therefore, resonant gate driver is adopted and efficiency is increased by 0.6%. In terms of the coupled-inductor, planar component is used and parameter optimization is also proposed to realize lower loss, including wingding loss and fringing loss caused by the air gap. A 500 kHz 36 W prototype has been designed to demonstrate theoretical analysis. In addition, comparison of drive loss between the resonant gate driver used in this paper and conventional driver implemented by Si8271 is made, revealing advantages of the resonant driver. Obtained efficiency was up to 92.1% at full load. [ABSTRACT FROM AUTHOR]

The modular multilevel converter (MMC) has attracted extensive research in recent years. An appropriate model is necessary to analyze stability or to design MMC controllers. Several published MMC models have been derived in single-phase form to simplify the modeling mathematics. However, little attention is given to the zero-sequence voltage, which introduces coupling in the single-phase model and leads to significant error. In this paper, after revealing the mechanism behind the zero-sequence voltage, a more accurate generalized single-phase MMC model is proposed, which eliminates the zero-sequence voltage coupling effect and is linearized based on harmonic state space (HSS) theory to precisely characterize the internal harmonic features of MMC. A systematic HSS modeling process is presented for both open-loop and closed-loop conditions. And the proposed model is generalized as it can incorporate different control strategy by controller transfer function substitution. Hence it is valuable to analyze MMC stability and dynamics. Model effectiveness is verified by simulation results. [ABSTRACT FROM AUTHOR]

Reduced dc-link capacitance interior permanent magnet synchronous motor (IPMSM) drives have many advantages, such as longer lifetime, reduced cost, and higher power density. However, due to the dc-link voltage fluctuation, the dc-link voltage utilization rate and the torque ripples are two major issues in flux-weakening operation region. It is important to consider these two issues comprehensively when a flux-weakening control method is adopted. In this paper, the IPMSM torque ripples caused by the dc-link voltage fluctuation and the overmodulation are analyzed in depth. In order to reduce the torque ripples and increase the utilization rate of the dc-link voltage, a novel adjustable maximum voltage based voltage closed-loop flux-weakening method is proposed. By switching between the minimum dc-link voltage control mode and the extended dc-link voltage control mode, the torque ripples can be reduced effectively and a nearly maximum utilization of the dc-link voltage can be realized. The proposed flux-weakening control method only depends on the dc-link voltage and the stator current vector reference. Experimental results on a 2.2-kW IPMSM drive platform are provided to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

A three-port converter (TPC) as a compact dc/dc energy conversion unit can effectively integrate renewable energy sources (RESs) and energy storage units (ESUs) into dc microgrids (MGs). In this paper, a series-resonance-based isolated TPC is developed to integrate photovoltaic (PV) and ESUs into dc MGs. A hardware decoupling approach using a series-connected capacitor in the half-bridge of the isolated TPC is proposed and studied. The decoupled power flow model among different ports is derived based on the equivalent circuit model of the converter, and the power transmission principle of the resonant circuit is analyzed. On this basis, considering the characteristics and operation modes of PV and ESU, which are connected at the two input ports of the TPC, a unified autonomous control method based on minimum value competition logic is proposed to coordinate the operation of PV and ESU, and achieve voltage regulation of the common bus in dc MGs. Simulation and experimental results are obtained in different test scenarios to demonstrate the effectiveness of the power decoupling effect and the proposed control method. [ABSTRACT FROM AUTHOR]

This paper proposes a high-frequency isolated dc/dc converter, whose switching frequency is 20 MHz. Meanwhile, the switch voltage stress is reduced based on optimal switch impedance. In the proposed converter, the switch can operate in ZVS condition, which can help to reduce the switching loss. A mathematical model of the proposed high frequency converter is built, which provides an effective design method for the system parameters. Meanwhile, the design method for PCB air-core transformer has been proposed and depicted. To verify the feasibility of the proposed converter and mathematic model, a 10 W prototype is built. [ABSTRACT FROM AUTHOR]

In this paper, a high step up converter consisting of an integrated quadratic-boost converter and a voltage doubler is proposed. The integration of the quadratic-boost converter makes the system easier to lift up its voltage gain through slightly increasing the duty ratio of the single switch. The voltage doubler further increases the voltage gain of the system as the turn ratio rises. The voltage stresses on the switch and the diodes are decreased for such cascaded topology. Different operation modes are analyzed and mathematical analysis of the converter is presented in detail. The leakage inductance contributes to realizing zero current switching of the diodes in the second boost stage and the doubler and the energy can be recycled to the load. A 38-W prototype is built to work as a vehicle LED driver. Experiments are conducted to verify the advantages of the proposed converter and the efficiency is 90% at the nominal operating point. [ABSTRACT FROM AUTHOR]

Inductive power transfer (IPT) systems designed with conventional methods offer optimum performance only at specific operational points. These methods are not applicable for dynamic IPT systems where both the coupling and load change throughout the operation. This study proposes a novel particle swarm optimization (PSO)-based parameter design method and aims to obtain a steady output voltage regardless of the coupling and load. The proposed method addresses the constraints of the conventional methods where the compensation capacitors/inductors are designed to resonate with certain other inductors/capacitors at the system's operational frequency. The S/CLC (primary series, secondary capacitor–inductor–capacitor) compensation topology is chosen in this research as it offers many appealing characteristics. The procedure to design an IPT system using the proposed method is presented. Two IPT systems, one designed with the proposed scheme and the other using conventional methods, are theoretically and experimentally compared in terms of fitness, voltage variation ripple (VVR), and power transfer efficiency (PTE). It is demonstrated that the fitness and the VVR of the conventional system are 1400.8% and 372.3% higher than those of the proposed system. [ABSTRACT FROM AUTHOR]

Impedance-source inverters using coupled inductors have been investigated as alternatives for providing high step-up voltages. However, leakage inductances of the coupled inductors have commonly led to lower overall effectiveness, in addition to generating high dc-link voltage spikes. The latter raises voltage stresses of switches, which in turn, may reduce the power levels of the inverters. A high step-up Y-source inverter has therefore been proposed in this paper to provide a high boost with a smooth dc-link voltage ensured by proper recycling of the leakage energy. These features have been verified by comparing simulation and experimental results of an existing Y-source and the proposed inverters. Factors compared are their respective boost ratios, voltage stresses, current stresses, and dc-link voltage spikes. [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]

A 1-MHz-modified single-ended primary-inductor converter (SEPIC) circuit is presented in this paper as an LED driver for automotive headlights. On the basis of traditional SEPIC, only a diode and two capacitors are added; therefore, the circuit structure is relatively simple and the volume is relatively small. High step-up capability is obtained with moderate duty cycle. Compared with traditional step-up circuit such as boost, low-voltage stress is gained which is beneficial to device selection. Zero-voltage switching is achieved at the same time to reduce switching loss. Planar inductors are used with the advantages of low profile and good thermal characteristic. Operational principle and parameters design process are introduced in detail. A 36-W prototype has been designed to demonstrate theoretical analysis. Obtained efficiency was up to 90.91% at full load. [ABSTRACT FROM AUTHOR]

The LC resonance between the line inductor and the dc-link film capacitor is an important concern in the reduced dc-link capacitance interior permanent magnet synchronous motor drive system. In this paper, an active damping method based on the virtual damping resistor is applied to suppress the LC resonance and improve the drive system stability. The performance of the damping resistor is analyzed in a systematic level, and possible configurations have been analyzed to obtain the optimal solution, which is proved to be the inductor current feedback (ICF) damping method. In order to realize the equivalent damping effect, the dc-link voltage feedback is applied to emulate the ICF-based active damping method by a step-by-step approach. Meanwhile, the grid voltage distortion will stimulate additional harmonics of the grid current in the reduced dc-link capacitance motor drives. Hence a feedforward compensation method is applied to suppress the grid current distortion arising from the distorted grid voltage, which has not been investigated in the previous related researches. Harmonics of the grid current are reduced and requirements of EN61000-3-2 can be satisfied by applying the proposed method. Experiments on a compressor drive platform equipped with the reduced dc-link capacitance are performed to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

A high-performance impedance-source converter utilizing switched inductor is proposed in this paper, which can be adopted in the applications demanding high-voltage conversion. The proposed converter not only retains the advantage of quasi-Z-source of sharing common ground between the input and output but also possesses the superiorities of enhanced boost ability and lower stresses as well as higher efficiency. Mathematical analysis of the converter and its performance comparison with other converters are presented in detail. Finally, a 100 W prototype is built and the experimental results are provided to verify the feasibility of the proposed converter. [ABSTRACT FROM AUTHOR]

Modular multilevel converters (MMCs) represent an emerging topology in medium-voltage (MV) and high-voltage applications. But for MV variable-speed motor drives, the MMC faces the challenge of large capacitor voltage ripple at low speeds. Delightfully, a hybrid MMC (HMMC) has proved to be potential in MV motor drives, since this topology has a lower capacitor voltage ripple and does not introduce any common voltage to the motor. This paper proposed a method to decrease the average capacitor voltage of the HMMC, which can effectively drive the motor at very low speeds without significantly increasing the submodule (SM) capacitance. Moreover, the selection of average capacitor voltage and the dimension of the SM capacitance are presented. Simulation and experimental results verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Wireless power and data transmission (WPDT) is required in many scenarios. This paper proposes a novel WPDT scheme based on capacitive coupling. The power transfer is analyzed, and the power circuit is equivalent to a double-sided LCC compensated wireless power transfer system. The modulation, injection, extraction, and demodulation circuits for data transfer are introduced. The function of each element in the proposed system is explained in detail. In order to facilitate the design of a practical WPDT system, the specific steps are summarized. Theoretical analysis on the interferences between the power transfer and data transfer indicates that the interferences can be significantly diminished by proper design. A 100-W WPDT prototype is built. The measured power transfer efficiency, from dc input to dc output, is 90.5%. The transferred data are correctly recovered in the receiver side at a data rate of 119 kb/s. The data circuit works well even though the coupling coefficient is decreased by 60.2%. The practically measured interferences between the power transfer and data transfer are quite small. The power transfer and data transfer are not affected by these interferences. [ABSTRACT FROM AUTHOR]

By using coupled inductors, impedance-source inverters can greatly increase their voltage step-up abilities at the expense of high voltage spikes at their dc-links due to leakage inductances. These voltage spikes can then cause damages and greater power losses. Therefore, to better clamp their dc-link voltages, various absorbing circuits have been proposed in this letter for forming a unique family of impedance-source inverters with even higher gains. The abilities of these inverters in clamping their dc-link voltages have been verified by experimental results presented at the end of the letter. [ABSTRACT FROM AUTHOR]

The capability of misalignment tolerance is vital for inductive power transfer (IPT) systems. S/SP compensation topology can provide a strong capability of misalignment tolerance if it is properly designed. This paper presents a detailed deduction process to acquire the optimal coupling coefficient, tuned at which the system can achieve minimum output voltage fluctuation. The impact of primary and secondary coupling inductance on output voltage fluctuation versus load variation was also analyzed. The output voltage fluctuation is not affected by the primary coupling inductance, but it decreases when the secondary coupling inductance is increased. Theoretical analysis was validated by both simulation and experiment. Three 200-W IPT prototypes were built. An overall efficiency of 94.1% was achieved when the coupling coefficient was 0.1733. The output voltage fluctuation was as low as 1.5% when the coupling coefficient increased by 34.5%, from 0.1288 to 0.1733. With a 900% rise in load resistance (from 80 to 800 Ω), the output voltage fluctuation decreased from 5.8% to 4.0% when the secondary coupling inductance increased from 136.3 to 250.0 μH. [ABSTRACT FROM AUTHOR]

Wireless power transfer (WPT) has attracted a large amount of attention owing to its inherent advantages such as convenience, safety, low maintenance, being weather proof, etc. A parameter tuning method is crucial for a WPT system due to its function of reducing reactive power and improving system efficiency. Three deficiencies of the conventional double-sided inductor–capacitor–inductor (DS-LCL) compensated system, i.e., low design freedom, weak high-order harmonic suppression capability, and discontinuous input current of a full-wave diode rectifier (FDR), are first analyzed by means of theoretical derivation, numerical calculation, and Pspice simulation. In order to overcome these disadvantages, a novel parameter tuning method is proposed. The characteristic of constant current output of the proposed DS-LCL system is analyzed, followed by a detailed derivation about secondary compensation inductance. Theoretical analysis indicates that the proposed system has four attractive characteristics: higher design freedom, reduced coil current, enhanced high-order harmonic suppression capability, and continuous input current of the FDR. The overall efficiencies of two comparative WPT prototypes, tuned by conventional and proposed methods, are 87.3% and 90.2%, respectively. Experimental results show great coincidence with theoretical analysis, demonstrating the superiority of the newly proposed parameter tuning method. [ABSTRACT FROM AUTHOR]

This paper presents a single-stage light-emitting diode (LED) driver based on a bridgeless power factor correction (PFC) converter and a half-bridge CLCL resonant converter for street lighting applications. The proposed single-stage topology integrates the PFC converter and the CLCL resonant converter by sharing active power switches. The bridgeless PFC converter adopts two buck–boost circuits operating in discontinuous-conduction mode to achieve input-current shaping. It uses two diodes instead of a rectifier bridge to reduce the power loss caused by the diodes. Owing to its superior soft-switching characteristics, the CLCL resonant converter is used. The proposed LED driver has superior features, such as high efficiency, near unity power factor, low total harmonic distortion, and relatively few diodes. A 100-W lab prototype is successfully implemented, and the experimental results verify the effectiveness and feasibility of the proposed LED driver. [ABSTRACT FROM AUTHOR]

In order to mitigate harmonics of the grid input current, passive filters are applied widely in the power electric systems. The LC resonance and the negative input impedance are important concerns in the reduced dc-link capacitance motor drive system. In this paper, an active damping control method is proposed to suppress the LC resonance by the direct damping current approach, which can formulate the pole distribution of the drive system. Different control laws have been analyzed, and the stability analysis is evaluated by the Routh–Hurwitz criterion. Meanwhile, the active damping control method is realized by the voltage command, which can overcome the limited bandwidth of the current controller. Since the generation of the direct damping current only depends on the dc-link voltage, the proposed active damping control method is robust. Compared with the virtual impedance methods, parameters can be accurately optimized by Bode diagrams after adopting the proposed active damping method. Simulation and experimental results are provided to verify the effectiveness of the proposed method. [ABSTRACT FROM PUBLISHER]

Circulating current is an undesirable phenomenon in modular multilevel converter which should be attenuated to reduce current stress and power losses. This letter presents a comparative study of the active and passive circulating current suppression methods. Voltage penalty of the active circulating current control is derived, and design of the passive circulating current filter parameters is provided. Simulations and experiments are performed to validate the analysis. [ABSTRACT FROM PUBLISHER]

Wireless power transfer (WPT) has attracted a lot of attention these years due to its convenience, safety, reliability, and weather proof features. First and foremost, the consistency of mutual model and T model of loosely coupled transformer (LCT) was deduced. The application scenarios of these two models were then concluded so as to choose suitable model in circuit analysis. Then, a new WPT compensation topology, which is referred to as LC /S compensation topology and consists of one inductor and two capacitors, is proposed. The constant-current-output (CCOut) characteristic of the newly proposed topology is analyzed in detail on the basis of the discussion about LC and CL resonant tank. The equivalent resistance of the rectifier, filter, and resistor circuit is also analyzed to simplify circuit analysis. Then, the current and voltage stress on each component and the system performance under imperfect resonant condition are studied with the help of MATLAB. The LCT is deliberately designed by the finite element analysis software ANSYS Maxwell as well because the coupling coefficient, primary, and secondary self-inductance have a significant impact on system efficiency, power level, and density. The LCT design approach employed in this paper can be extended to magnetic design of almost all WPT systems. Theoretical analyses are verified by both Pspice simulation and practical experiments. Practical output currents with transient loads show an excellent CCOut characteristic of LC/S compensation topology. [ABSTRACT FROM PUBLISHER]