Theoretical Limits of Power Transfer in Capacitive Wireless Charging Systems

This paper presents an analytical framework to determine the theoretical limits on the maximum power that can be delivered by capacitive wireless power transfer (WPT) systems suitable for electric vehicle (EV) charging. This framework yields analytical expressions for the output power and efficiency of a capacitive WPT system as functions of its geometrical and electrical parameters. The limits on system performance are imposed by physical constraints such as air breakdown, and application-specific constraints such as minimum acceptable system efficiency and allowable fringing field levels. The proposed analytical framework is used to predict and compare the maximum power transfer capability of different capacitive WPT systems designed to charge EVs with different chassis sizes and ground clearances. The analytical framework is validated using three 13.56-MHz 12-cm air-gap prototype capacitive WPT systems with power levels ranging from 800 W to 3.7 kW.