A novel EV wireless charging system with two-coil/three-coil hybrid application

A wireless power transfer system with three coils has some characters different from two-coil WPTs. In this paper, a two-coil/three-coil hybrid WPT system is proposed to obtain better performances. The hybrid system is constructed through adding the third coil to the frame of the sending coil of the traditional two-coil WPT system. The dimension of the additional coil is smaller than the original sending/receiving coils. The paper uses brute-force method to realize optimization design of key parameters in three-coil system. Different mutual inductances are obtained under the case with and without the third coil, which provides the control flexibility for the EV wireless charging system. MATLAB simulations are conducted to analyze system performances on power and efficiency. It is found that three-coil system has higher energy transfer efficiency when the load power at the receiving side is lower, while two-coil system has a higher efficiency when the load power is higher. With the findings, this paper puts forward a novel two-coil/three-coil hybrid WPT to obtain higher efficiencies under various power levels for an EV charging system. When the charging power is lower than the switching point, the system takes the three-coil frame while two-coil structure is employed when the power is above the switching point. The power switching point can be got from early simulations. Simulations show that efficiency above 70% can be always obtained under the power level from 31% through 100% for a wireless charging system of EV whose rating power is 1.6 kW.