A typical wireless Electric Vehicle (EV) charging system consists of a transmitting coil at the charging station and a receiving coil in the vehicle. In order to achieve a good separation between the coils, magnetic resonance coupling instead of conventional inductive coupling is used in these systems. The frequency characteristics of the wireless power transfer efficiency for different offsets between the transmitting and receiving coils of such a resonance-based wireless charging system were investigated both theoretically and experimentally. It was seen that if a fixed frequency is used, the resonance coupling system is very sensitive to imperfect positioning of the vehicle, leading to significant deterioration in efficiency. But by allowing for the transmit frequency to adapt to the position of the coils, the maximum efficiency can be maintained even for relatively large deviations of more than 20cm. Hence, in this work, a frequency agile resonance-based wireless charging system is proposed. The design senses the current in the transmitting coil and adapts the frequency such that maximum efficiency is maintained. The proposed system will provide significantly better power transfer efficiency than conventional fixed frequency designs when applied to EV charging under practical real-world scenarios.
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