Electric Parameter Tuning of Wireless Power Transfer Coil for Charging Interoperability of Electric Vehicles

The SAE J2954 recommended practice (RP) contains the power transfer frequency, electric values, and test procedure for the electric vehicle (EV) wireless power transfer (WPT). In particular, this document expresses the inductance range of the powering coil, the power receiving coil and the coupling coefficient (k) and the impedance values. It is very important that adhering the electrical parameters in the standard considering that the wireless charging system's compatibility. However, once the coil is processed, it is not easy to adjust the inductance of each powering coil, power receiving coil as well as the coupling coefficient of between transmitting coil and receiving coil. In this article, we introduce the method of tuning the coil's inductances and coupling coefficient by adjusting the effective permeability of the ferrite blocks. By controlling the permeability of ferrite blocks, self-inductance of coils and coupling coefficient are successfully adjusted. Through this idea, we obtained reasonable electrical parameters; inductance of ground-assembly coil, inductance of vehicle-assembly coil, and coupling coefficient.