Cross-coupling canceling method for wireless power transfer via magnetic resonance coupling

The phenomenon of cross coupling between coils is a widely discussed subject in various fields. In communication technology, for example, the resonator is used as a filter. Cross coupling affects the filter characteristic and therefore should be eliminated. The earlier studies, however, are either not applicable to wireless power transfer or lack a detailed treatment of wireless power transfer efficiency. Papers that do mention the undesirable effects of cross coupling on wireless power transfer characteristics do not provide an analysis of how cross coupling affects the transfer efficiency. In this study, we analyzed the effects of cross coupling on the overall efficiency, with a detailed comparison of the results with and without cross coupling. We discovered that at the resonant frequency, as the cross coupling increases, the frequency shift also increases, which causes the efficiency to deteriorate. From this result, we proposed four ideas for efficiency improvement. Among them, the frequency tracking method is most useful for efficiency improvement when the operating frequency is variable. When the operating frequency is fixed, the cross-coupling canceling method can be used to achieve maximum efficiency at the resonant frequency. We also discovered that load value optimization is not needed in the frequency tracking method because the simple tracking method can provide sufficient efficiency improvement.