A High-Efficiency GaN-Based Single-Stage 6.78 MHz Transmitter for Wireless Power Transfer Applications

A single-stage 6.78 MHz transmitter is proposed, which directly converts a utility ac input to a regulated, high-frequency (6.78 MHz) ac output for wireless power transmission. The topology integrates a totem-pole rectifier operating in a discontinuous conduction mode and an asymmetrical voltage cancellation controlled full-bridge inverter. Compared with the traditional cascaded multistage transmitters, this single-stage approach achieves high power efficiency over the full load range, utilizes fewer fast-switching devices, and shrinks the size of the converter. Constant current behavior at the output of the transmitter enables a fast response to a sudden load change. The operation and theoretical analysis of the single-stage transmitter is verified using a 100 W, GaN-based prototype. Experimental results demonstrate the capability of the converter to provide high power factor, low total harmonic distortion of the input current, and high conversion efficiency over the whole power range. The resulting prototype is suitable for implementation in wireless power systems where multiple consumer electronics loads are charged from a single transmitter.