Extended-Distance Wireless Power Transfer System With Constant Output Power and Transfer Efficiency Based on Parity-Time-Symmetric Principle

Maintaining constant power transfer while keeping near-unity transfer efficiency at varying transfer distances is a major challenge for existing wireless power transfer (WPT) system with multiple repeaters. In order to overcome the problem, this article proposes a novel WPT mechanism with multiple repeaters based on the concept of parity-time symmetry. First, the coupled-mode model of this WPT relay system is established. Then, the steady-state transfer characteristics of the proposed WPT system with an odd and even number of repeaters are analyzed. The theoretical analysis shows that whether an odd or even number of repeaters are inserted between the transmitting and receiving coils, the proposed system automatically achieves constant output power and transfer efficiency against the variation of the transfer distance without any tuning or feedback within a certain distance. The prototype with one repeater and two repeaters is implemented to verify the validity of the theoretical analysis. Experimental results show that the prototype with one repeater can transfer power with an invariant transfer efficiency of 91% and a constant output power of 15 W within a transfer distance of 420 mm. Similarly, the prototype with two repeaters transfers constant power of 15 W over a transfer distance ranging from 420 to 500 mm, and the transfer efficiency is constant near 89%.