A Current Weighted Multiple Input High Frequency Resonant Converter With Unified Phase-shift Modulation

Multiple input distributed generation system is widely used in the field of photovoltaic power generation as it has higher reliability than tradi tional single module. However, a multiple input structure leads to a complex control mode. The traditional phase-shift modulation cannot achieve the decoupling between the amplitude and phase of the output voltage. The change in phase caused by voltage regulation will bring circulating current. In view of above problem s, a unified phase-shift modulation and current weighed working mode which is based on multiple input high frequency resonant converter is adopted in this thesis to improve the performance of the system.The multiple input converter operates on high frequency AC bus. A unified phase-shift modulation is adopted to decouple the amplitude and phase of the output voltage and to make them be independently controlled. Two converters of different levels of power share the load current according to certain weight curve, to extend the high efficiency range. The AC working stage is analyzed and a phase sampling method is adopted. The driving circuit, resonant network, and main components are designed as an open loop work. A small signal model is accomplished through the constant frequency approximation, and the voltage feedback loop, current phase and amplitude feedback loop are realized. The working principle and paralleling characteristics are verified through simulation. The phase synchronization, wide-input range, power distribution and redundancy character are verified by an experiment platform.An experimental prototype is designed in this thesis with rated output of 50V/200 W, switching frequency of 100 k Hz, and it is debugged through both software and hardware. The results show that the circulating current is effectively reduced by the unified phase-shift modulation, and the high efficiency range has been extended by the current weighted working mode. The soft switching and a smooth output waveform are obtained to decrease the loss by the resonant network. The constant frequency approximation is used to simplify the modeling process. So the adoption of modified phase-shift modulation and current weighted working mode enhanced the reliability and redundancy, and the performance of the system is improved.