Power conversion system integrating OBC and LDC using tapped transformers for weight, volume, and cost reductions in electric vehicles

Abstract

Electric vehicle (EV) on-board chargers (OBC) use high-frequency transformers for isolation between the grid power and the propulsion battery. Additionally, low voltage dc-to-dc converters (LDC) require high-frequency transformers for high step-down and electrical isolation. Although a high-frequency transformer is used for isolation, it is desirable to minimize the use of magnetic materials because the isolation breakdown between the windings of the transformer occurs due to vibration. It also increases the weight and volume, and reduces the mileage of vehicles. Therefore, this paper proposes an OBC–LDC integrated system without additional windings by dividing the transformer windings used for the OBC. Depending on the connection state of the selective switch in the proposed system, it is divided into a propulsion battery charging mode and an auxiliary battery charging mode. At the same time, the selective switch converts the required transformer turns ratio in the changed operation mode. The proposed OBC–LDC integrated system is verified through prototype experiments. In addition, the volume and weight of a conventional vehicle charger and the proposed integrated charger are compared, and the economic benefits of the proposed charger are derived through cost model analysis (CMA). © 2023, The Author(s) under exclusive licence to The Korean Institute of Power Electronics.