Impedance Control Network-Based Inverters for High-Frequency Capacitive Wireless Power Transfer Systems

High-power large air-gap capacitive wireless power transfer (WPT) systems require paralleling either the semiconductor devices in their high-frequency inverters or paralleling the inverters themselves due to limited current rating of available gallium nitride (GaN) transistors. This paper introduces a method to parallel inverters in capacitive WPT systems suitable for electric vehicle (EV) charging based on an impedance control network (ICN) architecture. The ICN architecture helps combine power from two high-frequency inverters by effectively suppressing the impact of any mismatches between them, thereby doubling the power transfer capability of the capacitive WPT system. A comprehensive design methodology to design an ICN-based capacitive WPT system is presented. Furthermore, an auxiliary zero voltage switching (ZVS) circuit to achieve ZVS soft switching of all the inverters' transistors is also designed. The auxiliary ZVS circuit-based approach reduces the circulating currents in the matching networks and ensures equal power processing by both the inverters. For experimental validation, a 6.78-MHz 12-cm air-gap kilowatt-scale ICN-based capacitive WPT system is designed, built and tested up to 1800 W output power. The experimental results are in good agreement with the theoretical predictions.