500W 13.56MHz Class EF Push-pull Inverter for Advanced Dynamic Wireless Power Applications

Abstract

This paper will present the design process and construction of a 500 W 13.56 MHz GaN-based power inverter to enable advanced wireless power and wireless charging applications. Applications such as wireless charging of underwater vehicles, drones, mid-air drone-to-drone wireless charging, robotics and fast wireless charging of devices require power levels in the hundreds of watts range at MHz switching frequencies. These applications are dynamic and must operate without the need for precise coil alignment and fixed coupling coefficients, therefore switching at MHz frequencies is key for transferring power at larger air gaps, achieving better tolerance to coil misalignment and implementation of lightweight, high-Q single-turn coils and power dense electronics. The power inverter presented here is based on a push-pull load-independent Class EF topology that generates a sinusoidal output current with a constant amplitude and phase that do not change as the reflected impedance varies. Additionally, zero-voltage switching (ZVS) is maintained independent of the load value. These features allow the inverter to drive the transmitting coil at constant current whilst maintaining high efficiency and low noise regardless of the reflected load value without the requirement for a feedback loop, tuning or impedance transformation networks.