onsidering some comprehensive factors, such as wide voltage range at low voltage side and relatively high efficiency requirement, this paper adopts three-phase staggered parallel structure in power supply. In bidirectional dc-dc, the design and selection of igbt bridge arm of switch tube are made mainly by calculating the output capacitance parameters of inductors l1, l2 and l3 in main integrated circuit, and the output capacitance parameters of filter and capacitor cl.