Research On Three-phase Multi-resonant Converter With Wide Gain Range

With the shortage of energy and the aggravation of environmental problems,the development and utilization of new energy is becoming more and more important,and the promotion of electric vehicles driven by electric motors is also imperative.The charging power of electric vehicles is relatively large,and the voltage variation range is relatively wide.Therefore,it is necessary to study a DC/DC converter with wide gain and high efficiency applied to on-board chargers.Firstly,after analyzing the current status of LLC resonant research,a three-phase multi-resonant resonant converter(LLC-LC)is studied by introducing a trap into the three-phase LLC converter.The three-phase converter has a symmetrical structure,and a relatively wide gain range can be achieved only by frequency modulation.The transformer adopts a star-connected structure with self-current sharing capability,which can effectively avoid the three-phase current imbalance caused by mismatched resonance parameters.In addition,the three-phase drive signals of the converter have a mutual difference of 120 °,which effectively reduces the ripple of the output current and is beneficial to the realization of the converter’s compactness and high power density.Secondly,the working principle of the three-phase multi-resonant converter is introduced in detail.The equivalent circuit of one phase of the three-phase converter is obtained by the fundamental wave analysis method.The gain characteristics of the converter are derived from the equivalent circuit.In order to optimize the performance of the converter,the influence of the resonant network parameters on its gain,resonant current and excitation current is analyzed.At the same time,the gain curve is spaced and the ideal working range that can realize soft seitch is selected.Then,based on the analysis results and combined with the performance indicators,the parameter design of the three-phase LLC-LC multi-resonant converter and the selection of the device are completed.The hardware design and software design of the converter are completed by selecting the TMS320F28035 as the digital control chip of the system.Finally,the PSIM simulation software was used to verify the principle of the three-phase multi-resonant converter.At the same time,two experimental prototypes of three-phase LLC-LC converter and three-phase LLC converter with input 400 V,output250V-450 V and power of 3.3k W were built,and the experimental results were compared.An experimental prototype was set,and the experimental results were compared.Experiments show that although the efficiency of the three-phase LLC-LC converter is slightly lower than that of the three-phase LLC converter,the efficiency is still high in the entire output voltage range,with a maximum efficiency of 97.9%.When the voltage of the same width is output,the three-phase LLC-The frequency change range of the LC converter is smaller,which effectively broadens the gain of the converter,and solves the problem of difficulty in adjusting the voltage of the LLC converter at light load or no-load.