An LLC-DAB Bidirectional DCX Converter with Wide Load Range ZVS and Reduced Switch Count

An LLC-DAB bidirectional converter with reduced switch count as a DC-DC transformer (DCX) is proposed in this paper. It can achieve voltage regulation, full load range zero voltage switching (ZVS) for eight main switches and wide load range ZVS for four auxiliary switches, with consideration of the switch junction capacitors under different power direction.A small portion of total power is transferred through an auxiliary DAB circuit with the purpose of achieving voltage regulation and bidirectional power conversion; The main power are transferred through LLC circuit with easy PWM modulation scheme and high conversion efficiency. Different from the existing LLC-DAB DCX structure, the two secondary side transformer outputs are in parallel, and connected to the same full-bridge circuit. In this way, the auxiliary DAB circuit can not only adjust the output voltage, but also can inject current into the secondary side to help achieving ZVS of switches without synchronous rectifier (SR) circuit. The converter operation principle is analyzed under different power directions, and ZVS is analyzed with the consideration of all the switch junction capacitors. Based on these analysis, the design consideration are introduced. Finally, a 2 kW prototype is built up to verify the effectiveness of the proposed solution.