Circuit model based design and analysis for a four-structure-switchable wireless power transfer system

The four-coil wireless power transfer (WPT) technology can effectively improve the transfer efficiency. The high efficiency, however, cannot be obtained along the whole transfer distance due to the phenomenon of frequency splitting in the over coupled region. Aiming at this limitation, this paper presents a switchable WPT system to improve the overall efficiency by changing the number of working coils. The switching conditions for the designed system are determined based on the analysis of the transfer efficiencies of four structures, which is deduced through modeling the equivalent circuits. The simulation results well comply with the experimental results and both of them indicate that the switchable system can greatly improve the overall transfer efficiency along the whole transfer distance. The overall efficiency of the experimental system can reach above 70% at 9.97 MHz without additional complexity, which is higher than any single structure system.