A Three-Coil Constant Output Wireless Power Transfer System Based on Parity-Time Symmetry Theory

In a three-coil wireless power transfer system with relay coils, the transmission efficiency and output power of the system decreases with changes in the adjacent coupling coefficients. Controlling the power of three-coil wireless power transfer systems is also a significant challenge. To solve these issues, a three-coil wireless power transfer system based on parity-time symmetry is proposed in this paper. First, a three-coil parity-time wireless power transfer system was modeled based on a circuit model. Then, the transmission and gain characteristics of the three-coil parity-time wireless power transfer system were analyzed. It was found that when the system is in a parity-time-exact region, it can maintain a constant transmission efficiency and output power, and its output power is independent of the coupling coefficient. In addition, based on the output characteristics of the three-coil parity-time wireless power transfer system, a power control method and a working range detection method were proposed to attain a constant power output. Finally, a three-coil parity-time wireless power transfer system was experimentally tested.