Parity-Time-Symmetry-Based WPT Systems with Homogenous Transmitter Coils for Drone Applications

Parity-time (PT) symmetry has proven to be helpful in wireless power transfer (WPT) systems, as it provides constant output power and efficiency independent of the coupling factor k. The problem facing PT-symmetry WPT systems is their inability to soft switch due to the introduction of a negative resistance, which decreases the total system efficiency. In this paper, we propose a control method to achieve soft switching in a specific charging area by combining a PT-symmetry-based WPT system with a homogenous transmitter coil. The homogenous transmitter coil will provide a constant coupling factor between it and the receiving coil within the homogenous area, allowing for fixed frequency control. The fixed frequency will be slightly higher than the resonance frequency, thereby achieving soft switching. Outside the homogenous area, the controller will switch to resonance tracking mode to achieve PT-symmetry, thereby extending the misalignment tolerance. This study demonstrates a 24-V 100-W 1-MHz WPT system. The experiment shows that the proposed control strategy can yield 3-4% higher total system efficiency within the homogenous area while having constant power output and transfer efficiency. Furthermore, 100% of the transmitter pad area can be utilized, which proves that high misalignment tolerance is achieved.