Resonance Parameter Optimization And Switching Control Strategy Of Wide Output Resonant Converter

New energy vehicles are beginning to be favored by consumers due t o their environmentally friendly and non-emission characteristics,and the per capita ownership of electric vehicles in my country is also increasing year by year.However,the insufficient number of public charging piles on the market and the different nominal voltage levels of power batteries of various models have seriously affected the convenience of charging new energy vehicles.Therefore,an isolated DC-DC converter with a wide voltage output range is of great significance to the development of chargi ng equipment.LLC resonant circuit has the characteristics of soft switching,high powe r density,etc.,and is widely used in electric vehicle charging.This thesis proposes a wide voltage output range LLC resonant converter with four operating modes for the needs of wide output voltage,and analyzes the working principle of the converter in detail in each mode.The fundamental wave analysis method and the time domain analysis method are used to determine the gain range of the converter in each mode to ensure the theoretical validity of the wide output characteristics.The resonant parameters of LLC resonant converter with wide voltage output range are optimized.Because the quality factor Q and the inductance ratio h in the resonance parameters not only det ermine the gain characteristics of the topology,but also affect the loss of the circu it.After using the platform approximation method to approximate the resonant current,the effective value analytical expression of the resonant current in the frequency modulation control and the phase shift control is calculated,and the relationship bet ween Q and h and the circuit loss is obtained.Through the input impedance model,the analytical expression of the peak gain of the topology is calculated,and the influence of the resonance parameters on the peak gain is clarified.Under the three conditions of meeting the minimum loss,realizing zero voltage turn-on,and meeting the gain requirements,the appropriate Q and h parameters are optimized.According to the gain range of the four operating modes in the new topology,the appropriate mode switching point is selected,and the control strategy for multi-mode switching is formulated to achieve the purpose of wide output voltage.And the introduction of hysteresis swi tching to avoid the slight disturbance of the input voltage from affecting the output.The steady-state state trajectory of the electrical quantities in working mode 2 and working mode 3 is explored,and the optimization period is inserted in the mode swit ching with reference to the state trajectory control method,which improves the speed of the circuit to re-enter the steady state after switching.Based on the above theoretical analysis,an experimental prototype was designed and built,and the correspond ing experimental verification was completed.Experimental results show that the propos ed topology can achieve the design requirements of a wide output voltage range under the premise of ensuring soft switching characteristics.The closed-loop load cut experiment shows the stability of the circuit output,and the work mode switching experiment proves the effectiveness of the proposed optimization method.