Inductive Power Transfer with Resonance for Wireless Charging of Batteries in Electric Vehicles

Abstract

This report investigates inductive power transfer with resonance for wireless charging of electric vehicle (EV) batteries. The inspiration for the topic came from the paper Basic experimental study on helical antennas of wireless power transfer for Electric Vehicles by using magnetic resonant couplings by T. Imura, H. Okabe and Y. Hory [7]. The paper presents laboratory results of more than 97% power transfer efficiency at a distance between the coils of up to 20 cm. The coils used are air cored and the frequency is in the MHz range, the largest amount of power that was transferred was 100 W.For charging the battery of an EV in a reasonable amount of time, the power has to be high; in the kW range. When such high power is to be transferred, MHz switching frequencies will be a problem for the semiconductor switches of the power supply. Therefore, it is interesting to investigate the feasibility of wireless power transfer at lower operating frequencies. In this master thesis inductive power transfer by use of resonance are studied for the frequency range; 3-20 kHz. A prototype of the resonant circuit has been built in the laboratory. In order to increase the flux density and guide the flux, each of the coils is wound on a Ferrite E-core. The load is modelled by a resistor. A half-bridge inverter has been designed and built, and is used as power supply for the system. The efficiency of power transfer for the prototype is more than 65% for a distance between the coils of up to 7.5 cm. The power transferred is about 14 W. The power can be increased by building a system with higher component ratings. The conclusion of this thesis is that inductive power transfer with resonance seems relevant for further research.