Range-Adaptive Wireless Power Transfer Based on Differential Coupling using Multiple Bi-directional Coils

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