Development of MHz power converters for wireless power transfer applications

Operating wireless power transfer (WPT) systems in the megahertz (MHz) range is a promising approach to more compact solutions with a greater tolerance to misalignment. Class E/EF power converters, due to the single-ended gate driving and soft switching, are particularly attractive. However, there are numerous challenges in designing MHz converters. In this paper, the development, design, and testing of Class E/EF converters are systematically introduced. Wide band gap (WBG) devices, including gallium nitride (GaN) and silicon carbide (SiC), are employed. In particular, a cascode GaN/SiC configuration can increase the voltage rating and thus the power level. To maximize flexibility, a circuit design with a main board and different daughter device boards is developed. This circuit can work as power inverter or rectifier, in class E or EF and in single-phase or push-pull structures. A WPT system is finally built based on the developed inverters and rectifiers between which the power is transferred wirelessly through a pair of PCB air-core coils. Experimental results have been obtained that validate the development of the converters and WPT systems working at 6.78MHz with a power rating of over 1 kW.