Improved Dual Battery Charging System for Grid Connected Bi-directional EV Charger

This paper proposes an isolated low power bidirectional on board electric vehicle (EV) dual battery charging topology with grid connectivity and unity power factor (UPF) operation. The proposed EV charging system is able to exchange active and reactive power demand by either side of the bidirectional charger. The primary EV battery operates in a bidirectional charging mode through a dual active bridge converter with a phase shifting operation whereas the auxiliary battery operates in a unidirectional mode to provide power to the EV auxiliary units. This improved topology of dual battery charging system operates independently to maintain necessary amount of battery voltage without affecting the transformer efficiency. The active and reactive power demand is met by the high capacity EV primary battery, whereas the auxiliary battery is intended only for unidirectional controlled power flow. In this paper the EV charging topology is investigated with a front end decoupled power control and a secondary battery sliding mode control (SMC) for bi-directional power flow operation. The mathematical model of the proposed converter is discussed through state space averaging technique to analyse the converter dynamics with variable demand during bi-directional power flow operation. A MATLAB and Simulink is used to develop the proposed circuit topology of dual battery EV charging system for a 4kW single phase grid connected system. The prototype is designed to validate the DC-DC power flow with a high frequency isolation.