Transformer for contactless electric vehicle charging with bidirectional power flow

This paper investigates the use of air-gap transformers in wireless energy transfer, particularly in electric vehicles. Air-gap transformers have very low coupling factor due to the length of the air-gap between the vehicle and the charging platform. A novel approach has been proposed to achieve bidirectional control of power. The effect of the variable air-gap on the efficiency of the system was also determined. The system was designed in MATLAB/Simulink using a switching frequency of 13 kHz, the switching was done at the frequency of the resonant tank and an appropriate compensation capacitance was selected using the series-series topology. A transformer rating of 25kVA was selected and connected to a low voltage DC grid of 1kV rating. The simulation results produced an accurate bidirectional control of power flow as well as an optimum coupling factor / air-gap length, verified using Finite Element Analysis.