Research On High Efficiency Resonant Bidirectional DC-DC Converter

With the intensification of energy crisis and environmental problems,the DC microgrid based on distributed power supply and energy storage system has been widely concerned for its superior performance.As the load fluctuates constantly,an efficient Bidirectional DC-DC converter is needed to connect the energy storage device to the DC microgrid bus to maintain constant bus voltage.Aiming at the problem that the existing Bidirectional DC-DC converter is easy to lose the soft switching characteristics in the wide load range.In this paper,a high-efficiency resonant Bidirectional DC-DC converter is proposed.And carrying out in-depth research,from the realization conditions of the soft switching,the resonant cavity structure and the control strategy.The main contents are as follows:1.This paper summarized the research background and research status of Bidirectional DC-DC converter at home and abroad,discussed the essence of soft switching technology,and mainly introduced the technical points involved in this paper.The voltage regulation characteristics and power transmission capacity of different resonators are compared.The control strategy of the converter is analyzed,and it is decided to adopt the mixed control strategy of Phase-shift and Frequency-modulate(PSFM).This paper introduced the main modeling methods of Bidirectional DC-DC converter,analyzed in detail the fundamental wave component method based on Fourier decomposition,and decided to model the converter with different frequency-doubling components.2.In order to solve the problem that series resonant bidirectional DC-DC converter is difficult to realize Zero Voltage Switch(ZVS)in a wide load range,which leads to low operating efficiency,a high efficiency series resonant bidirectional DC-DC converter(HE-SR-BDC)topology is proposed.The realization condition of ZVS when parasitic capacitance of switch tube is taken into account is derived,and the resonance parameters are calibrated,so that the energy stored in the resonator can discharge the parasitic capacitance completely.By adopting the hybrid control strategy of shift plus frequency modulation,the implementation range of ZVS is widened by increasing the switching frequency and phase shift angle when the converter is running lightly.The fundamental wave analysis method is used to model the system in time domain and phasor domain.The working characteristics of the converter are analyzed.Finally,the system parameters are given and the positive andnegative operation effect is verified.3.A high efficiency multi-resonant bidirectional DC-DC converter(HE-MR-BDC)is proposed to solve the problem of low energy transfer efficiency of series resonant converter and the difficulty of ZVS implementation caused by low switching current.On the basis of series resonance,a parallel resonance structure is introduced.The LCLC resonator has three resonant frequencies,which can transmit fundamental frequency and triple frequency energy,reducing the resonator circulation.The resonant cavity current is the superposition of fundamental frequency and triple frequency components,which increases the zero-crossing slope of the resonant current,increases the turn-off current,and further broadens the implementation range of ZVS.The fundamental frequency and tri-octave components after Fourier decomposition are considered to model the system,analyzed its working characteristics,and deduce the realization conditions of soft switch with parasitic capacitance.Finally,the parameters of the High-Efficiency Multi-Resonant Bi-directional DC-DC converter are designed,and a simulation system is built for verification.And compared with the running effect of series converter.