Bi-directional Operation Mode of LLC/CLLC DC/DC Converter for On Board Charger of 800V Battery Systems

Global Vehicle OEM’s are raising the battery voltage to increase the mileage of electric vehicles and reduce the battery charging time. A bidirectional on-board charger (OBC) is also required for Vehicle to Grid (V2G) and Vehicle to Load (V2L) operation. Recently, ICCU (Integrated Charging Control Unit), a product that integrates OBC and LDC (Low-Voltage DC/DC Converter) circuit and housing, has been developed. In this paper, we propose LLC/CLLC bidirectional DC/DC converter for OBC circuit in 800V battery system. In forward mode, it operates as LLC full-bridge resonant converter to achieve a wide output voltage range. In reverse mode, the DC link voltage can be designed to be lower than in forward mode by operating as a CLLC half-bridge resonant converter. The proposed converter uses SiC-MOSFET, so it satisfies high voltage and is implemented in a small package. The 11 kW prototype of the proposed bidirectional resonant converter was built and tested to verify the proposed operation.