A Frequency Tuning Series-Series WPT System with Wide Coupling and Load Ranges

Frequency tuning is widely used in wireless power transfer (WPT) systems for output control. In this paper, a design method of series-series (SS) WPT systems employing frequency tuning control is proposed to achieve a constant current (CC) and constant voltage (CV) battery charging profile over a large coupling and load ranges. Particular attentions have been paid to guarantee zero-voltage switching (ZVS) in the whole CC/CV charging process and the whole coupling range. The relationship between frequency splitting (FS) and frequency bifurcation (FB) is theoretically analyzed and the feasible operating zone for frequency tuning is figured out in kilowatt applications with ZVS. Then, secondary winding is optimized for overall efficiency improvement. A 3.1kW WPT system is designed and built for experiments. The measured DC-DC efficiency of the system with a coupling coefficient range of 0.13-0.31 peaks at 96% and it is higher than 90% throughout CC charging process.