High efficiency contactless power transfer system for electric vehicle battery charging

In this paper, a contactless charging system for an electric vehicle (EV) battery is proposed. The system is composed of three parts, a high frequency power supply from a full-bridge inverter with frequency modulation, a loosely coupled transformer that utilizes series resonant capacitors for both the primary and secondary windings, and a rectification output circuit that uses a full-bridge diode rectifier. With carefully selected compensation network parameters, zero-voltage switching (ZVS) can be ensured for all the primary switches within the full range of an EV battery charging procedure, which allows the use of low on-state resistance power MOSFETs to achieve high frequency operation and system efficiency. The design of loosely coupled transformer is simulated and verified by finite element analysis (FEA) software. A peak efficiency of 96.6% is achieved with a 4 kW prototype with an 8 cm air gap transformer and 156 kHz switching frequency.