Shielding Design for High-Frequency Wireless Power Transfer System for EV Charging With Self-Resonant Coils

This article provides a complete coil and shielding design solution for a 6.6 kW electric vehicle (EV) wireless power transfer system based on compact self-resonant (SR) coils. Due to the presence of a conductive vehicle body above the receiver coil, vertical fringing flux must be shielded in any EV wireless charger. Using high-frequency SR coils, parasitic capacitance introduced by standard shielding design approaches degrades the quality factor of the coils. In this article, the high-frequency parasitic capacitance introduced by the magnetic and conductive shielding materials is analyzed in detail, and a shielding geometry optimization method is proposed. Using ferrite and an additional dielectric spacer, prototype aluminum-backed SR coils are fabricated to validate the modeling. The total thicknesses of the transmitter and receiver coils are only 11.4 and 7.4 mm, respectively. The prototype coils achieve 92.3% dc-dc efficiency and 7.1 kW/dm(3) volumetric power density. This article demonstrates the first 6.6 kW WPT system for EV charging using compact megahertz-SR coils including a complete magnetic and conductive shielding implementation.