Wireless Power Transfer System Adaptive to Change in Coil Separation

In this paper, we present a wireless power transfer (WPT) that is adaptive to change in coil separation. For analytic design of the WPT system, a new design method which does not require calculating the voltages and currents in the system is presented. The proposed design method allows us to have perfect impedance matching theoretically for the WPT system using capacitor circuits connected to the sending and receiving coils. Closed-form design equations are provided for straight-forward application of the new design method. In order to compensate the variation of the mutual coupling between the two coils due to the change in separation, we propose a new switchable capacitor array circuit. For verification of the new design method and the new switchable capacitor array circuit, we have fabricated and measured a WPT system operating at 370 kHz. Measured results have shown a good agreement with theoretical responses, and the reflected power ratio smaller than 3% has been achieved by using the proposed switchable capacitor array circuit over the 5:1 change of coil separation.