Research Of Bidirectional LLC Resonanton Converter

With the rapid development of technologies such as new energy sources and electric vehicles,high-power power converters that can achieve two-way power flow have become more and more widely used.Among them,the single-phase LLC resonant converter has the advantages of simple structure,low EMI,high power density,etc.The inverter side switch tube can realize the ZVS of the full load range,and is widely used in facilities such as car charging piles.However,due to problems such as large output ripple and high voltage and current stress,single-phase LLC resonant converters are difficult to apply to high-power applications.This paper studies in detail the topological characteristics and working principles of the three-phase LLC resonant converter with △-type connection in forward and reverse operation.Each bridge arm on the inverter side of the converter is conducted with a phase difference of 120° each other.The superposition effect of the current after the phase shift is used to reduce the output ripple,and when the three-phase resonant network parameters are different,the △-type connection can also realize automatic current sharing.While inheriting the advantages of single-phase LLC,it solves the problem of single-phase LLC.Problems in high-power applications.The model of the three-phase LLC resonant converter is more complicated.After analyzing its working mode in detail,in order to simplify the calculation of the model and the analysis of the working characteristics,this paper derives its equivalent single-phase model through analysis,and uses the fundamental wave analysis The method analyzes the operating characteristics of its single-phase model,obtains the operating characteristics of the three-phase LLC resonant converter forward operation and reverse operation modes,summarizes the conditions of the real soft switching,and uses the extended description function method to find the small Signal model,and give the converter closed-loop control system and resonant cavity parameter design method.On the basis of theoretical analysis,simulation software is used to build a model for simulation verification,and the simulation waveforms at different operating frequencies are compared with theoretical waveforms to verify the correctness of the theoretical analysis.Finally,an experimental platform was built to realize the two-way transmission of energy,and the pulse frequency modulation(Pulse Frequency Modulation,PFM)method was used to stabilize the output voltage of the converter.The typical experimental waveforms of different working areas were given to verify the correctness of the theoretical analysis.And the feasibility of the plan.