Charging Strategy of Integrated Onboard EV Charger with Small Intermediate Capacitor

The purpose of this paper is to investigate charging strategies for integrated electrolytic capacitorless onboard chargers (OBC) in electric vehicles (EVs). An integrated OBC shares power converters and inductance with the traction system. An electrolytic capacitor is avoided in DC link of this integrated OBC. Thus, volume is reduced and reliability is improved for the power conversion system. In this paper, a charging strategy is proposed for this integrated system with uncontrolled rectification, where active switches are kept off in the power inverter on machine side. Consequently, a virtual DC-link voltage is with a half-wave shape. An extended phase-shift (EPS) operation is proposed for high-frequency DC/DC converters with this charging strategy, respectively. By designing a dedicated modulation and control strategy, sinusoidal charging power and the satisfied grid current are achieved for the system. Both theoretical analysis of operation modes and experimental verification with laboratory prototypes have been presented for the proposed charging strategy.