Extended-Range Wireless Power Transfer System Based on High-Order PT Symmetric Principle

Using relay coils is an effective way to increase the transfer distance of the wireless power transfer (WPT) system. Based on the high-order parity-time (PT) symmetric principle, the three-coil WPT system can obtain constant output power and transfer efficiency when the total transfer distance changes. However, the coupling coefficient between the transmitting coil and the relay coil must be equal to the relay coil and the receiving coil, which is quite difficult to meet in actual application. This paper proposed a high-order PT symmetric three-coil system equipped with a variable inductor, a variable capacitor and a buck converter. The variable inductor is used to regulate the equivalent inductance of the transmitting coil, so that the system can meet the symmetric coupling coefficients constraint even if the corresponding distances are asymmetric. The variable capacitor is used to keep the natural resonant frequency constant, which is also required in the PT symmetric system. The addition of a buck converter leads the system can output constant power when the load varies or the equivalent inductance varies. A simulation prototype is presented in PSIM, verifies that the proposed system can output constant power even under the asymmetric distances condition.