Effect of load dependence of efficiency in a multi-receiver WPT system

Most batteries require constant voltage to charge; therefore, wireless charging receivers need a constant voltage circuit, commonly a DC-DC converter (DDC). On the other hand, Resonant Magnetic Coupling enables multi-receiver charging. As a result, we need to design a wireless charging system for multi-receivers with a DDC. In cases of multi-receiver charging with different positions, the input voltage for a DDC in the stronger coupling receiver rises. Since there is a practical limit of DDC input voltage, we need to design the wireless charging system, not to exceed the limit. Through our work, we investigated the character of the load dependence of efficiency, and made clear that robustness to load variation determines the DDC input voltage by simulation and experiment. In conclusion, efficiency robustness to load variation is advantageous for single receivers, but not for multi-receivers in different coupling conditions.