Design and Stray Field Evaluation of Inductive Power Transfer in Electric Vehicle Charging

The influence of magnetic stray fields in the vicinity of a vehicle is a concern when inductive power transfer (IPT) is used for wireless charging for electric vehicles. To accurately evaluate the stray fields, the design of the coils and the chassis configuration should be considered. In this paper the analysis and design of a series-series compensated 3.3kW IPT charger is presented. A prototype of the charger is constructed and mounted on a plug-in hybrid electric vehicle. The stray fields are measured at rated power and compared with finite element analysis simulations. The simulated and measured magnetic flux density are in good agreement. The highest measured magnetic flux density is 1.67 mu T at the left tire with the ground assembly misaligned by 100 mm. It is only 6.2% of the flux density allowed for the general public in the ICNIRP standard. It is concluded that for low power IPT chargers, the requirement on leakage flux density is easily fulfilled.