Study on Coil Sizing and Shielding Materials High-Power Wireless Power Transfer Systems for Electric Vehicle Charging

Since the international standard SAE J2954 is approved, reference coil systems are available for wireless power transfer systems up to 11 kVA. For systems with higher output powers, recent research studies propose larger coils and the usage of multiple ferrite layers. In this paper, a comprehensive study on the influence of different shielding materials and coil sizes on the magnetic behavior of circular pads (CP) and double-D pads (DDP) is conducted in order to determine design recommendations for high-power charging. The coupling coefficient and the leakage fields are used to assess different coil combinations. The design study shows that aluminum shielding is more suitable for CP in terms of magnetic leakage while ferrite material is more suitable for DDP. Furthermore, the results of the design study highlight the need for sufficiently large secondary coils to achieve reasonably high coupling coefficients and position tolerance. It is shown that the low coupling of small secondary coils will cause higher currents and therefore increase leakage fields. In conclusion, design recommendations for CP and DDP are provided.