Maximum Output Power Tracking for Wireless Power Transfer System Using Impedance Tuning

The output power of a magnetic resonant coupling wireless power transfer (WPT) system drastically decreases when the distance of couplings coils changes due to impedance mismatch. A maximum power point occurs at only one optimal distance. These characteristics are caused by limitation in design stage. This paper proposes a new impedance tuning method of tracking, for maximum power point, by adjusting resonant frequencies and capacitance values according to the varied distance. The theoretical performance is analyzed using the Thevenin equivalent circuit of the WPT. In the experiment, a prototype of two-coil wireless power transfer system is created. The power transferred to a resistive load for the cases of constant frequency and the proposed impedance tuning method are compared. Simulation and experimental results show that the maximum power point tracking under coil distance changes is made possible. This work can be useful in a design stage of wireless power transfer.