High-Performance Multi-MHz Capacitive Wireless Power Transfer System with an Auxiliary ZVS Circuit

Abstract

A high-performance multi-MHz capacitive wireless power transfer (WPT) system utilizing a single inductor-based auxiliary zero voltage switching (ZVS) circuit and suitable for electric vehicle (EV) charging is proposed in this paper. The auxiliary ZVS circuit provides the required inductive current to achieve ZVS of the transistors in the WPT system's full bridge inverter. A procedure to optimally design the ZVS circuit is also presented. Compared to the conventional approach to achieving ZVS, the auxiliary ZVS circuit improves the WPT system's performance by reducing the circulating currents in its matching networks. The benefits of the proposed auxiliary ZVS circuit in terms of efficiency and inverter transistor RMS currents are quantified by comparing the proposed system to a system utilizing the conventional ZVS approach. The benefits of the proposed approach are also experimentally validated by building two 6.78-MHz 12-cm air-gap kilowatt-scale capacitive WPT prototypes, one with and one without the auxiliary ZVS circuit. The prototype with the auxiliary ZVS circuit achieves 5% higher efficiency and transfers 32% higher power than the conventionally designed prototype.