Structure-Reconfigurable Wide Gain Series Resonant Converter For On-Board Charger

To deal with a series of issues such as energy crisis and global warming,more and more countries are adopting the solution of replacing traditional fuel vehicles with electric vehicles.As an important charging equipment for electric vehicles,on-board charger is attracting more and more attention and study.In the process of charging the power battery of electric vehicle,it is necessary for the on-board charger to maintain high efficiency while maintaining a wide output voltage range.Therefore,it is significance to study a DC/DC converter with wide gain and high efficiency for the development of vehicle charger.To meet the requirement of wide output voltage range and high efficiency,a structure-reconfigurable wide gain series resonant converter is proposed in this thesis.The fixed-frequency pulse width modulation(PWM)control strategy is employed,and the switching frequency equals to the series resonant frequency.Through the control of the active switches,the inverter unit of the converter can switch between the full-bridge inverter structure and the symmetrical half-bridge inverter structure,and the rectifier unit can switch between the full-bridge rectifier structure and the active boost rectifier structure.In this way,the structure of the converter can be reconstructed online,and then two operating modes of buck and boost are obtained.It solves the problem that the traditional single structure converter can not take into account the wide gain and high efficiency.The operation principle of the two modes of the converter is analyzed in detail,and the equivalent circuit of each stage and the time domain equation of current and voltage are given.Based on the energy conservation relationship between input and output in a switching cycle,the expression of voltage gain of the converter is derived to ensure the validity of wide gain in theory.To achieve zero voltage switching(ZVS)in the whole operating range and improve efficiency,the ZVS characteristics of the proposed converter are analyzed in detail.Combined with the time domain equation of current and voltage,the realization condition of ZVS is solved.The main parameters of the converter are designed under the condition of ensuring the realization of ZVS.To avoid voltage pulsation and current impact in the process of mode switching,this thesis makes a reasonable design of the turn-on and turn-off sequence of the switches in the process of between buck mode and boost mode transition of the converter.A simple PWM control strategy is adopted to realize smooth transition between modes and improve the stability of converter operation.Based on the above theoretical analysis,a 2.5k W experimental prototype with output voltage range of 200～500V is built.The operation principle and characteristics of the converter are verified by experiments.The results show that all switches can realize ZVS and all rectifier diodes can realize zero current switching(ZCS)in the whole operating range.The high efficiency is always maintained,and there is no obvious voltage fluctuation in the process of mode transition.