Active-Relay-Based Wireless Power Transfer System With Efficiency Optimization Over Load Variation

To achieve an efficiency improvement for a threecoil wireless power transfer (WPT) system with the load variations, an active-relay-based WPT system has been proposed. In the proposed system, the relay coil is in the same plane as the transmitting coil with tightly wound, which can be regarded as part of the transmitting coil without affecting the transmission distance. In order to realize a continuous impedance matching of different load conditions, the switchingcontrol capacitor (SCC) is used in the relay coil, which makes the relay coil an active structure. A collaborative control method is proposed for SCC to obtain the maximum efficiency of the system with load variations. Moreover, the additional losses of SCC have been analyzed. Finally, the effectiveness of the proposed system is verified experimentally.