Design to Eliminate Frequency Bifurcation in Transformers for Wireless Charging of Electric Vehicles

In this paper, a transformer design method with a compensation network is proposed for a wireless power system for electric vehicles. The objective is to prevent a bifurcation in the frequency response of the transferred power, which causes undesirable resonance conditions in the system. An evaluation using finite element analysis is presented and applied to a case study, from which the number of turns of the primary and secondary windings of the transformer can be established to help reduce the mentioned bifurcation. The results show that lowering the self-inductance of the secondary coil allows the bifurcation of frequency to be reduced. In addition, power transfer can be maximized by optimizing the self-inductance of the primary coil. The proposal is applied in a wireless power transfer system for an electric scooter, in which the transformer is designed to transfer a maximum power of 150 W without frequency bifurcation and with an efficiency greater than 97 %.