Optimal Study of Resonant Wireless Charging Coils for Electric Vehicles

In order to optimize the coil design of electric vehicle (EV) high power resonant wireless power transfer (WPT) system and improve its transfer efficiency, an equivalent circuit model of two-coil series-series topology is analyzed in this paper. Four optimal factors that affect the system transfer efficiency are proposed, i.e. the number of coil turns, the mean radius of coils, the transfer distance and the load. Based on the consideration of the equivalent series resistance of the coils, it can be found that the number of coil turns, the mean coil radius, and the load have the optimal values for the optimal transfer efficiency, while the shorter the transfer distance is, the higher the transfer efficiency is. By using the simulation software COMSOL, similar relationships between four factors and the transfer efficiency can be achieved with the calculation results. Moreover, by repeating the calculation using the simulation coil resistance, the differences between the calculation results and the simulation results are explained. Therefore, the WPT coil optimal method with proposed four optimal factors is verified through calculation and simulation.