A Novel Multi-port Bi-directional Inductive Power Transfer System with Simultaneous Main and Auxiliary Battery Charging Capability

Abstract

When the battery in an electric vehicle (EV) is charged by an inductive power transfer (IPT) system, in general, the transmitted power is charged to the main battery used for the traction system on the EV at first. Next, the auxiliary battery is charged by the stored energy in the main battery through an isolated DC–DC converter. This causes an increase in the number of the power conversion stage and devices used. Therefore, this paper proposes a novel multi-port bi-directional IPT system that is able to charge both of the main and the auxiliary batteries simultaneously. In the proposed system, the number of power conversion stage and the devices used in it, specifically two diodes and two inductors, can be reduced. In addition, the design method of the novel system and the method for controlling the transmission power are described. Furthermore, the characteristics of the transmission power and efficiency (i.e. power loss) of the resonant circuit are derived from the theoretical analysis, and then the validity of the theoretical analysis is verified by the experiments. From the experiments, in Primary-side Coupled Mode, the maximum percentage errors were 7.2 % and 0.8 % in the transmission power and the resonant circuit loss, respectively, when the total transmission power to the main and auxiliary batteries was 1100 W. In Primary-side Non-coupled Mode, the percentage errors were 0.1 % and 23 % in the charging power and the resonant circuit loss, respectively, when the charging power of the auxiliary battery was 100 W. From the above, the validity of the theoretical analysis was verified.