Hybrid-Level Modulation Scheme for Dual-Bridge Series-Resonant Converter

This article proposes a hybrid-level modulation (HLM) scheme to achieve full load range zero voltage switching over various voltage gains for dual-bridge series-resonant converter. According to the load conditions, HLM includes two parts. At heavy load, a variable-frequency symmetrical level modulation (VFSLM) scheme is offered to ensure the complete commutation of the bridge legs with soft-switching operation. In addition, the optimal root mean square of the inductor current can be achieved, which further benefits the transfer efficiency. At light load, the switching frequency demanded by VFSLM is much higher than the resonant frequency. So, a dual asymmetric level modulation (DALM) scheme is proposed to prevent devices from hard-switching operation within a moderate range of changes in frequency. Furthermore, the method of identifying control variables with DALM is analyzed for overall efficiency optimization. The developed approach is validated on a 6.6-kW on-board-charger whose output voltage varies from 220 to 470 V.