Wireless power transfer based on current non-linear PT-symmetry principle

In this study, the authors propose a novel circuit topology based on the current non-linear parity-time (PT)-symmetry principle. The exact analytical solutions of transfer efficiency and resonant frequency are deduced, a state switching phenomenon is observed, and the mathematical expression of the critical coupling coefficient (kappa(c)) corresponding to the state switching point is provided. When the coupling coefficient (kappa) is >=kappa(c), the system has two real frequencies and can maintain near 100% transfer efficiency theoretically. When kappa < kappa(c), the system has only one real frequency, and the transfer efficiency attenuates rapidly. The correctness of the theoretical model is verified by simulation and experiment. Results show that when the distance between the two coils (38 cm in diameter) varies from 10 to 42.5 cm, the transfer efficiency remains similar to 95%, without the need for any tuning. Theoretical analysis and experimental verification show that kappa(c) increases when the load resistance increases and the natural resonant frequency or the self-inductance of the Rx coil decreases. Furthermore, the system can maintain the equivalent current of the Tx and Rx circuits when kappa >= kappa(c), which is convenient for controlling the circuit current, and suitable for the case of small load and large current.