High-Performance 13.56-MHz Large Air-Gap Capacitive Wireless Power Transfer System for Electric Vehicle Charging

This paper introduces a high-performance large airgap capacitive wireless power transfer (WPT) system for electric vehicle charging. This system operates at 13.56 MHz, and utilizes coupled-inductor based L-section matching networks that provide gain and reactive compensation. The high operating frequency and coupled-inductor matching network design are shown to significantly enhance the system's efficiency and reduce its size. Efficiency is further enhanced by realizing the matching network capacitors entirely using parasitic capacitances, thus eliminating the losses associated with on-board capacitors. A 13.56-MHz 12-cm air-gap prototype capacitive WPT system is designed, built and tested. This system transfers 884 W at an efficiency of 91.3%, achieving a power transfer density of 29.5 kW/m
²
. Additionally, the prototype system achieves a peak efficiency of 95% when transferring 348 W. Compared to a prototype 6.78-MHz capacitive WPT system, the 13.56-MHz system exhibits up to 53% reduced losses and 69% reduced inductor volume.