High-Efficiency High-Power-Transfer-Density Capacitive Wireless Power Transfer System for Electric Vehicle Charging Utilizing Semi-Toroidal Interleaved-Foil Coupled Inductors

This paper presents a high-performance kilowatt-scale capacitive wireless power transfer (WPT) system for electric vehicle charging. This system achieves effective power transfer across a large air-gap by operating at a multi-MHz frequency (13.56 MHz), and by utilizing L-section matching networks that provide gain and reactive compensation. To achieve high efficiency at the high operating frequency, the matching network inductors are constructed as semi-toroidal structures with interleaved-foil coupled windings. This new coupled inductor design greatly reduces the inductor's ac resistance, with a measured 46% reduction compared to a conventional solenoidal coupled inductor. To further enhance performance, the matching network capacitors are comprised solely by the parasitic capacitances of the system, thereby eliminating on-board capacitors prone to dielectric breakdown and high-frequency losses. A 13.56-MHz 12-cm air-gap prototype capacitive WPT system incorporating these innovations is designed, built and tested. This system transfers 2.25 kW at an efficiency of 90%, achieving 29.6 kW/m
²
power transfer density. The system achieves even higher efficiencies at intermediate power levels, with a peak efficiency of 94% at 320 W, and 93% efficiency at 2 kW.