Multi-port Inductive Power Transfer System Considering Charging Auxiliary Battery in EVs

In electric vehicles (EVs), the main battery used for the traction system and an auxiliary battery for the low-voltage system are equipped. When inductive power transfer (IPT) is used to charge the main battery, it requires high-voltage ratings and high-cost switching devices for the onboard AC/DC converter. In addition, the onboard auxiliary battery is generally charged by an isolated DC/DC converter connected to the main battery. Due to this configuration, the high-voltage rating switching devices are needed for the isolated DC/DC converter in addition to IPT. For this, the utilization rate of the high-voltage rating switching devices for IPT is low, and that increases cost. A previous work proposed a multi-port system to integrate the transformer for the isolated DC/DC converter and the transmission coil for IPT to reduce the cost. In the previous system, though the high-voltage rating devices could be reduced, the number of the switching device was the same as in the general system. Therefore, to reduce the cost, this paper proposes a multi-port onboard converter that integrates an IPT system and an auxiliary battery charger system by using high-voltage rating switching devices for IPT. This integration reduces the number of switching devices by four compared to the general system. In this paper, the operation and characteristics of the proposed system are clarified, and its validity is verified by the experiment. Regarding the experimental result, it is confirmed the characteristics of the transmission power agreed well with the theoretical result.