In this paper, the control of stabilizing bus voltage and increasing system reliability of electrolytic capacitor-less variable frequency speed control system is investigated. The problems of power coupling and low reliability of electroless capacitor inverter drive under conventional double closed-loop vector control are discussed. By analyzing the DC bus voltage stability, the use of BP neural network PI control in the speed loop is proposed in order to improve the reliability of the motor under speed variation. The proposed method reduces the sensitivity to speed changes by changing the controller parameters according to the speed given and the feedback value, thus preventing the bus voltage overshoot. A simulation model and an experimental platform are built to verify the feasibility of the control strategy of the electrolytic capacitor-less variable frequency speed control system, and it is proved that the proposed control strategy can effectively improve the reliability of the system.

This paper proposes a family of high voltage gain DC-DC converter based on active switched inductor (ASL) and switched capacitor (SC) units. By configuring a set of ASL unit and two sets of SC units, high voltage gain is achieved while maintaining low voltage stress and low current stress of components in the converter. And the external characteristics of the converter are analyzed. At the same time, three extended topologies of this converter have been proposed to further improve the voltage gain. Also, the pros and cons of the three extended topologies and their scope of application are analyzed. Finally, the external characteristics of the proposed converter were verified through experiments, and the correctness of the three extended topology schemes was analyzed through PSIM simulation. The experiment results and simulation results show the converter and its extended topology have good performance in achieving high voltage gain and low voltage and current stress at the same time.

The application scenarios of multi-load magnetically coupled resonance (MCR) wireless power transfer (WPT) are becoming more and more extensive, and the independent control of the voltage of multiple loads is imminent. A two-degree-of-freedom control strategy for a dual-frequency dual-receiving coil system is proposed in this paper. Based on low-frequency SPWM, the frequency of the carrier wave is only three times the frequency of the modulating wave. Fundamental voltage and harmonic voltage at switching frequency are obtained on the primary side. A buck converter is cascaded in front of the inverter. By controlling the two degrees of freedom, the duty cycle α of the buck converter and the modulation degree M of the SPWM, the amplitude of the voltage of the two frequencies at the output of the inverter can be independently controlled. The theoretical results are verified by experiments. The experimental results show that the dual-frequency dual-receiving coil system based on dual-degree-of-freedom control can achieve independent control of the output voltage under different loads.

To suffice the requirement of FCV, a DC-DC converter must have continuous high voltage gain, continuous input current, common grounding between input and output, low electromagnetic interference issues. Besides these, DC-DC converter should be compact with lower voltage stress across different components. A new DCDC converter is proposed which is structured by combining quasi switched boost network and switched capacitor network in this paper to fulfill above requirements. The proposed converter steady state analysis, stress analysis, comparative analysis is presented in this paper. A 200 W power rating converter is validated in experiment.

This paper presents a novel hybrid modulation method based isolated high frequency (HF) bidirectional inverter for AC microgrid application. Bidirectional current-fed converter has been employed to interface the energy storage and intermediate fluctuating dc bus. A new hybrid modulation techniques consisting of fluctuating-dc-modulation (FDM) at low frequency (LF) scale and secondary modulation (SM) at HF scale has been proposed for the current-fed converter. The zero current soft switching (ZCS) of primary side devices and zero voltage soft switching (ZVS) of secondary side devices of front-end current-fed full-bridge converter is realized. The back-end full bridge inverter has been utilized to interface the fluctuating dc bus and AC microgrid. A rotating partial hybrid pulsewidth modulation (RP-HPWM) has been introduced. One leg of inverter is commutated at low switching frequency while the other leg is operated at high switching frequency for partial period of line frequency cycle. Besides the high switching frequency operated switches are only commutated at low value of current flowing through them. Thus, switching losses of the back-end inverter can be considerably reduced. Rotating mechanism is used to equalize the switching losses of four switches of the inverter. The low frequency (LF) fluctuating dc bus allows the reduction of dc-link electrolytic capacitor. This paper presents operation and analysis of the complete inverter topology implementing the proposed hybrid modulation scheme. Simulation results using PSIM9.0.4 and experimental results from a lab prototype clearly validate effectiveness of the proposed modulation scheme.

This paper presents a six-pulse low frequency (LF) fluctuating high voltage dc bus based power system architecture for the fuel cell vehicles (FCVs) application. A novel hybrid modulation techniques consisting of six-pulse modulation (SPM) at LF scale and secondary modulation and 33% sine pulse width modulation (33% SPWM) at high frequency (HF) scale. Three-phase ac waveforms are produced for the propulsion system in FCVs. It significant reduces the switching losses of the bidirectional dual-stage inverter: 1) the zero current soft switching (ZCS) of primary side devices and zero voltage soft switching (ZVS) of secondary side devices of front-end current-fed full-bridge converter is realized. 2) at any moment, only one leg of back-end 3-phase inverter is switched at HF while the other two legs are kept in on or off state. This tremendously reduces the bidirectional inverter's switching losses and improves the system efficiency. Besides, switching loss can be further reduced since all the inverter switches are switched at the low current range. The LF fluctuating high voltage dc bus allows the elimination of large electrolytic dc-link capacitor. This paper presents the operation, analysis, and design of a bidirectional inverter implementing the proposed hybrid modulation technique. Simulation results obtained from power electronics simulation software PSIM and experimental results from the lab prototype clearly validate the effectiveness of the proposed modulation technique.

The proposed converter has the following features: 1) zero current commutation (ZCC) and natural voltage clamping (NVC) eliminate the need for active-clamp circuits or passive snubbers required to absorb surge voltage in conventional current-fed topologies; 2) Switching losses are reduced significantly owing to zero-current switching (ZCS) of primary side devices and zero-voltage switching (ZVS) of secondary side devices. Turn-on switching transition loss of primary devices is also negligible. 3) Soft-switching and NVC are inherent and load independent. 4) The voltage across primary side device is independent of duty cycle with varying input voltage and output power and clamped at rather low reflected output voltage enabling the use of low voltage semiconductor devices. These merits make the converter good candidate for interfacing low voltage dc bus with high voltage dc bus for higher current applications. Steady state, analysis, design, simulation and experimental results are presented.

A novel bidirectional snubberless naturally commutated soft-switching current-fed three-phase DC/DC converter is proposed. This proposed secondary modulation technique naturally clamps the voltage across the primary side devices with zero current commutation (ZCC) eliminating the necessity for active-clamp circuit or passive snubbers. Switching losses are reduced significantly owing to zero-current switching (ZCS) of primary side devices and zero-voltage switching (ZVS) of secondary side devices. Soft-switching and natural voltage-clamping (NVC) is inherent and load independent. The proposed bidirectional converter shows better performance i.e. high efficiency, high density, high reliability, small volume, light weight and low cost. These merits make the converter promising for electric/fuel cell vehicles, front-end dc/dc power conversion for solar/fuel cell inverters and energy storage. Steady state analysis, design, and experimental results are presented.

This paper explains steady-state operation and presents steady-state analysis and design of a three-phase AC link active-clamped zero-voltage switching (ZVS) current-fed dc/dc converter. The proposed converter maintains ZVS of all power semiconductor devices over wide range of load and supply voltage, achieved by the energy stored in the boost inductors for auxiliary clamp devices, and leakage inductance (aided by magnetizing inductance) for main devices. The proposed converter also combines the advantages of three-phase configuration with zero-current switching (ZCS) of rectifier, making it a competitive topology in the area of power supplies/converters especially for low voltage dc sources with high voltage amplification ratio. Simulation and experimental results are illustrated for wide variations in input voltage and load on a tested 300 W prototype.