Wireless Charging of Electric Vehicles: Planar Secondary Coil Position vs. Magnetic Field

The paper provides a parametric investigation on the magnetic field produced by a wireless power transfer (WPT) system to recharge the battery of an electric vehicle (EV), varying the position of the secondary coil in the car underbody. The considered WPT charging system operates at the frequency of 85 kHz with a power of 7.7 kW. The WPT system creates a very strong magnetic field that can be critical for human exposure to electromagnetic fields (EMF) and for immunity of implanted medical devices. The presence of the conductive body-frame of the vehicle permits to shield the magnetic field inside the cabin, but beside the vehicle the field level is significant. Several factors (installation position of the secondary coil; coil alignment; vehicle shape and dimensions; ground clearance; body material; etc.) that influence the magnetic field behavior are considered. Different EV-WPT coil configurations are examined and the magnetic field levels are predicted by numerical simulations. From the obtained results general guidelines for the optimal position of the WPT system are provided.