Range-Adaptive Wireless Power Transfer Based on Differential Coupling Using Multiple Bidirectional Coils

Wireless power transfer systems using coupled magnetic resonances are susceptible to the transfer distance variation between the transmitter (Tx) and receiver (Rx) since the coupling between Tx and Rx is highly position dependent. Once the transfer distance deviates from the optimum one, the coupling will be either excessive or weak, which results in power transfer efficiency (PTE) degradation. This article presents a Tx structure consisting of multiple subcoils oriented in opposite directions to keep the coupling relatively constant over an extensive range of transfer distances. The proposed design can achieve a PTE of 88-70% with a transfer distance varying from 0 to 70 mm and a PTE of 85-60% with a misalignment of 0-80 mm at a 40 mm transfer distance. The radius of the Tx and Rx is 84.6 and 45.1 mm, respectively. The measured PTE of the proposed design is better than 70% with a 0-50 mm transfer distance while the misalignment changing from 0 to 50 mm. The proposed system is much less sensitive to the transfer distance variation than the convention system and has a great potential for wireless charging applications.