Magnetic Design Considerations for High-Power Wireless Charging Systems

Abstract

This article proposes methods of predicting and preventing thermal failure within high-power ferrite structures of electric vehicle (EV) wireless charging inductive power transfer (IPT) by improving their ferrite layouts. A high-power IPT magnetic design suitable for wirelessly charging an EV at 50 kW using a heuristic approach is presented, where the chosen design achieves reduced heating within the magnetic structure. Recommendations are made that both avoid ferrite fracturing due to magnetic hotspots and cause temperature differentials across ferrite tiles, and regarding airgap distribution between ferrite tiles to reduce loss-inducing circulating flux within the ferrite structure without reducing coupling. Power transfer was simulated in ANSYS and PLECS under misaligned conditions, and validated experimentally with 93.7% system efficiency. Thermal tests performed under rated volt-amps found the magnetics temperatures (after 30 min) could be reduced from 168 to 67 °C using an improved magnetic layout that reduced the thermal gradients within the ferrite tiles by 70%. Leakage fluxes were targeted and validated to be below 15 μT, 950 mm from the center of the vehicle under rated power and worst-case misaligned conditions.