Magnetic field distribution in a WPT system for electric vehicle charging

The objective of this paper is to discuss major factors that affect the magnetic field distribution of a wireless power transfer (WPT) system for electric vehicle (EV) charging. Both analytical and simulation approaches with a 3D finite element method (FEM) are employed to analyze the flux distribution in the system and its surroundings. The purpose of the work is to provide design guidelines for an efficient WPT system that conforms to international standards on safety and radiated EMI. To verify the obtained results, a full-scale prototype is built and tested up to 20kW power level. On the sending side, the system contains a PFC rectifier followed by a multiphase series resonant inverter connected to a transmitting coil. The receiving side is comprised of a magnetically coupled receiving coil tuned with a series-connected capacitor and a rectifier with a resistive load to emulate a battery. The coils are of a rectangular shape with 70 cm outer dimension, wound with 7 turns of litz wire, shielded with a layer of ferrite, and supported with aluminium plates. The receiving coil is attached to a steel plate that emulates a car chassis. The operating frequency of the system is 85 kHz. The calculations, simulations, and measurements are performed at various power levels and variable gap between coils (from 100mm to 300 mm). Furthermore, the effect of the coil misalignment on the magnetic field is analyzed and discussed based on two different misalignment situations. The theoretical and simulation results of this paper are in a good agreement with experimental measurements which validates the presented methodology.