An Optimal Design Methodology for LCL Resonant Converter by Considering both Modulation Strategy and Circuit Parameters

The inductor-capacitor-inductor (LCL) resonant converter possesses the advantage of high efficiency, bidirectional power flow, zero voltage switching (ZVS), etc. The commonly used modulation strategy for LCL converter is multi-phase-shift, among which triple phase shift (TPS) can reach the highest efficiency owing to the most control degrees-of-freedom (DOFs). However, when adopting TPS strategy, existing literatures only design phase shift angles elaborately without considering circuit parameters design, so there is still room for improvement of the converter efficiency. This paper proposes a design methodology for LCL converter by considering both modulation strategy and circuit parameters. First, multi-harmonic frequency domain model for bidirectional LCL resonant converter is set up, through which analytical expressions of the voltages and currents of the resonant tank are obtained. Then, to minimize the conduction loss and achieve full-range ZVS, an optimal design procedure for TPS strategy is carried out. Furthermore, a global optimal TPS modulation strategy for LCL converter is proposed by adding circuit parameters design into the procedure. Finally, a 250/150 V, 1000 W bidirectional LCL resonant converter prototype is built. Compared with the optimal TPS strategy, the peak converter efficiency with the global optimal TPS strategy considering circuit parameters design increases by 2.2% from experimental result. The theoretical and experimental results demonstrate the excellence of the proposed global optimal TPS design methodology.