电动汽车直流充电系统LLC谐振变换器软开关电压边界分析

Analysis of Soft Switching Voltage Boundary of LLC Resonant Converter for EV DC Charging System

LLC谐振变换器以其优异的性能被广泛应用于电动汽车直流充电领域。针对电动汽车宽输出电压范围、高转换效率的充电需求,该文对直流充电模块后级全桥LLC谐振变换器软开关运行的输出电压边界进行了分析。零电压开通(ZVS)上边界处,变压器励磁电感参与谐振,其二次侧等效峰值电压与负载电压相等,整流二极管临界导通;ZVS下边界处,谐振电流与谐振腔的输入电压同时过零,LLC谐振变换器运行于临界感性区间。该文利用时域分析法详细分析了变换器ZVS上下边界处的工作状态,计算出变换器软开关运行所允许的输出电压范围,揭示了变换器的软开关特性与工作频率、谐振参数之间的关系,为变换器的参数设计和变频控制提供了理论指导。最后,通过仿真和实验对理论分析进行了验证。

LLC resonant converter has been widely used in the field of DC charging for electric vehicles due to its excellent performance.Aiming at the charging requirements of electric vehicles with wide output voltage range and high efficiency,the output voltage boundary of the full bridge LLC resonant converter in DC charging module was analyzed in this paper.At the upper boundary of(zero voltage switching,ZVS),the magnetizing inductance of the transformer resonates,whose equivalent peak voltage of the secondary side is equal to the load voltage,and the rectifier diode conducts critically.And at the lower boundary of ZVS,the resonant current and the input voltage of the resonator cross zero at the same time,and the converter runs in the critical inductive region.In this paper,the working state at the ZVS upper and lower boundaries of the converter was analyzed in detail by the time-domain analysis method.The output voltage range of the converter operated in the soft switching state was calculated,and the relationship between the soft switching characteristics of the converter and the working frequency and resonance parameters was revealed,which could provide guidance for parameter design and frequency conversion control of the converter.Finally,the analytical method was verified by simulation and experiment platform.