High-Performance Capacitive Wireless Power Transfer System for Electric Vehicle Charging with Enhanced Coupling Plate Design

This paper presents a capacitive wireless power transfer system for electric vehicle charging that achieves high efficiency and record-breaking power transfer density. This high performance is enabled by multi-MHz operation, innovatively designed matching networks, and enhancements in the design of the capacitive coupling plates. The enhanced coupling plate design includes the use of circular plates enveloped in a high-breakdownstrength dielectric material. This prevents arcing and allows kilowatt-scale power transfer across large air-gaps. Multiple 6.78MHz 12-cm air-gap prototype capacitive WPT systems are built and tested to systematically validate these coupling plate design enhancements. The first system utilizes 150-cm(2) coupling plates constructed from square-shaped bare copper sheets, and is only able to transfer 146 W at an efficiency of 84% before arcing occurs between a coupling plate and the vehicle chassis. The coupling plates are then enveloped in a thin layer of polytetrafluoroethylene (PTFE), enabling 590 W of power transfer at an efficiency of 88.4% before arcing intervenes again. The coupling plate design is then further enhanced by replacing the 150-cm(2) square plates with circular plates of the same area, also enveloped in a layer of PTFE. This system achieves a power transfer of 1125 W at an efficiency of 85%, corresponding to a power transfer density of 37.5 kW/m(2). Finally, a prototype system with 118-cm(2) PTFE-enveloped circular coupling plates is shown to transfer 1217 W at an efficiency of 74.7%; hence, achieving a power transfer density of 51.6 kW/m(2), which exceeds the state-of-the-art for large air-gap capacitive WPT systems by more than a factor of two.