双向隔离 LCL 谐振变换器 PFM + TPS 四自由度 优化调制策略

Inductor-capacitor-inductor (LCL) resonant converter possesses the advantage of zero voltage switching (ZVS), bidirectional power flow capability, high efficiency, etc. But the output voltage tends to be unregulated and the efficiency deteriorates under light load with traditional pulse frequency modulation (PFM) strategy. Therefore, the common modulation strategy for bidirectional LCL resonant converter is multiple phase shift, among which triple phase shift (TPS) has the most control degrees-of-freedom and can reach the highest efficiency. However, existing literatures set the switching frequency as a fixed value when adopting TPS strategy, so there is still room for improvement of the converter efficiency. An optimized PFM + TPS four degrees-of-freedom modulation strategy was proposed for bidirectional LCL converter based on multiple harmonic frequency domain model. First, multiple harmonic frequency domain model of bidirectional LCL converter is set up, and analytical expressions of the voltage and current of the resonant tank were calculated, which overcomes the drawback of low accuracy of the traditional method using first harmonic approximation. Then, optimized design for four different phase shift modulation strategies and PFM + TPS modulation strategy proposed were carried on, and optimal results for each strategy were quantitatively compared from two perspectives, namely the ZVS characteristics and the sum of square of the root mean square value of the primary side current and secondary side current. Finally, a 900 W bidirectional LCL converter prototype was built. Compared with TPS strategy, the peak efficiency of the converter with PFM + TPS strategy increases by 1. 55% from experimental measurement. The theoretical and experimental results demonstrate accuracy of the multiple harmonic frequency domain model and the superiority of the proposed PFM + TPS modulation strategy.