用于车载充电的双向CLLC变换器设计

Design method of bidirectional CLLC resonant converter for on-board charger applications

摘要:

为拓宽车载充电机（on-board charger, OBC）双向充放电工作范围并提高充电效率,用PFC（power factor correction）级联高效CLLC(电容-电感-电感-电容)谐振拓扑实现电网电压与电池电压之间能量双向转换。同时为解决CLLC谐振拓扑在宽范围工作时参数设计困难的问题,提出一种参数设计及优化方法,采用基波分析法（fundamental harmonic analysis, FHA）对谐振网络建模,推导充放电增益的归一化方程,提取出影响谐振变换器增益和效率的关键参数,对比分析关键参数的变化对拓扑各项性能的影响规律,进而总结参数的设计及优化原则。结果表明:影响谐振变换器双向运行最重要的参数是匝数比和谐振电容,其中变压器匝数比主要影响CLLC变换器的充放电效率,谐振电容值影响充放电宽范围输出的最佳工作区,通过分析给出了双向传输功率同等级时匝数比和谐振电容的最佳取值范围。应用CLLC拓扑,双向车载充电机可实现双向超宽范围运行,整机充电效率最高可达94.5%,CLLC效率可达97.5%。

Abstract:

To broaden the working range of on-board charger (OBC) for bidirectional charging and discharging and improve the charging efficiency, the power factor correction (PFC) cascaded high-efficiency CLLC resonant topology was used to realize the bidirectional conversion of energy between grid voltage and battery voltage. Meanwhile, in order to solve the problem of difficult to design parameters when CLLC resonant topology works in a wide range, a parameter design and optimization method was proposed. Fundamental harmonic analysis (FHA) was used for the modeling of resonant network. The normalized equations of charging and discharging gains were derived, and the key parameters affecting the gain and efficiency of the resonant converter were extracted. The influences of the changes in key parameters on the topology performance were compared and analyzed, and the parameter design and optimization principles were summarized. Experimental results show that the most important parameters that affected the bidirectional operation of the resonant converter were transformer turns ratio and resonant capacitance. The transformer turns ratio mainly affected the charging and discharging efficiency of the CLLC converter, and the value of the resonant capacitor affected the best working mode of the wide range output between the charging and discharging mode. The best value range of transformer turns ratio and resonant capacitor was given when the bidirectional transmission power was at the same level. By applying CLLC topology, the bidirectional on-board charger could achieve ultra-wide range operation. The charging efficiency of the whole machine reached 94.5%, and the efficiency of CLLC reached 97.5%.