A High Efficiency High Density DC/DC Converter for Battery Charger Applications

Increased attention is being paid to the solid-state-transformer (SST) based charging station which requires a high efficiency high power density DC/DC stage. This framework would provide universal charging for all electric vehicles (EVs) no matter their battery voltage is 400 V or 800 V. In this paper, a two stage DC/DC converter consisting of a three-phase (3P) CLLC converter and four-phase interleaving Buck converter is proposed to achieve a wide output voltage range from 200 V to 800 V with bi-directional energy transfer capability. With SiC devices, a PCB winding based six-leg integrated transformer is used for the 3P transformer, and a PCB winding based EI core is used for the negative coupling inductors. The detailed design process of integrated magnetics is presented. A 12.5 kW prototype with over 97.7 % efficiency and 100 W/in3 power density is built to verify the feasibility of the proposed structure.