Topology and Control Scheme of OBC-LDC Integrated Power Unit for Electric Vehicles

Abstract

This paper proposes a novel integrated low-voltage dc-dc converter (LDC) and onboard battery charger (OBC) for electric vehicles (xEVs) that share heatsinks, terminals, sensing circuits, and circuit components between both parts. The proposed OBC-LDC integrated power unit (OLPU) can be simplified by modifying the internal connections of the vehicle, thus eliminating the cost of high-power cables. In addition, the OLPU decreases the number of circuit components and increases the total power density by combining or sharing heatsinks, terminals, sensing circuits, and circuit components. Further, the proposed circuit satisfies the performance characteristics of conventional OBCs and LDCs and can be operated as such. Moreover, a simultaneous charging method for both a high-voltage battery and a low-voltage battery is suggested through an additional operational mode that results from the integration. This paper also specifically describes the operating characteristics and the design method in each mode. Design considerations, including possible problems with the integrated circuit structure, are presented, and an additional compensation circuit is suggested to solve these problems. The prototype is built, and experiments are carried out to verify the performance and validity of the proposed power unit.