Robust 3-D Wireless Power Transfer System Based on Rotating Fields for Multi-User Charging

A wireless power transfer system for multi-user charging is proposed to demonstrate a robust quasi-uniform power efficiency in a 3-D space. It employs a set of balanced magnetic coils excited with phase-shifted currents on the transmitting side to feature omnidirectionality. In this article, two transmitter structures, 2-coil and 3-coil systems are discussed and compared. These systems produce a quasi-uniform magnetic field magnitude regardless of the locations of the receiving coils provided that the coils point to the center of the transmitting system sphere at the same distance. A simulation platform is established for the proposed method. Experimental results at 2MHz substantiate a uniform spatial efficiency and bound the average error of analytical calculations within 10%. Furthermore, the proposed method with rotating fields based on phase-shifted currents shows that the 3-coil system yields a higher efficiency and a lower efficiency spread, 6.8% improvement on average efficiency and 88.7% reduction on efficiency variance, compared to the 2-coil system.