A wireless power transfer system based on quasi‐parity–time symmetry with gain–loss ratio modulation

Abstract

Wireless power transfer (WPT) systems based on parity-time (PT) symmetry can realize robust power transfer against the fluctuation of distance. There is an exceptional point (EP) that partitions the PT-symmetric and PT-broken phase, and it is nonadjustable at the conventional system with unity gainloss ratio unless changing circuit parameters, which limits the improvement of its transfer performance. This paper proposed a novel quasi-PT-WPT system based on gain-loss ratio modulation. The proposed system can operate under different gain-loss condition with constant transfer power and efficiency regardless of coupling coefficient variation at the PT-symmetric phase, which can enhance either the maximum transfer efficiency or distance alternatively. The proposed system consists of a nonlinear gain with adjustable gain-loss ratio to enable the transfer performance control, which is implemented by the virtual impedance. Experimental results verified the correctness of the theoretic analysis and implied the inherent contradiction between the transfer efficiency and distance.frequency tuning, parity-time (PT) symmetry, virtual impedance, wireless power transfer (WPT) | INTRODUCTIONWith the development of theories and hardware for nearfield magnetic coupling wireless power transfer (WPT), the WPT technique has made progress in practicality and gained great popularity in the last several decades. There is no doubt that WPT shows great commercial potential due to its technical advantages of safety and convenience, especially in some sceneries that are not convenient to apply wired power transmission. There are more and more applications that start to apply WPT techniques, including implantable medical devices (IMDs), 1 mobile portable terminals (MTPs), 2 underwater autonomous vehicles (UAVs), 3 and electric vehicles (EVs). 4 A practical WPT system must deliver power reliably to these modern devices mentioned above, which requires a robust WPT system. However, the transfer efficiency and power of the conventional WPT system are influenced by the transfer distance, since the electric-magnetic coupling strength between the transmitter and receiver varies with the separated distance. 5 In order to stabilize the transfer power and efficiency, many different control strategies and physical methods have been proposed for WPT systems in recent years, including high-order compensation network, 6 active impedance matching, 7 adaptive network tuning, 8,9 and heuristic control algorithms. 10 Actually, WPT control methods can be divided into three categories: primary-side-only control, 11 secondary-side-only control, 12 and dual-side control. 13 Primary-side-only control is indirect