Precise Impedance Matching for Class- E Driven MHz WPT System Based on Mobius Transformation

In MHz wireless power transfer (WPT) systems, load conditions often fluctuate due to coil misalignment, impedance changes, or compensation errors. However, the Class-E power amplifier (PA), which commonly used in high-frequency wireless power transfer, is sensitive to load variations and thus lacks overall robustness. To enhance the stability of the Class-E PA, an impedance matching network (IMN) is required, but the IMN itself has limited design degrees of freedom, making it challenging to accurately pull multiple load points to designed working conditions. Addressing these challenges, this paper proposes a novel matching network design method based on Mobius transformation. The IMN designed with proposed method enables a Class-E PA to operate efficiently at different situations as changing resistive loads or compensation errors. The effectiveness of the design has been verified through simulation and experiment. The system designed with proposed method has 84%-87% DC-DC system efficiency with 40% mutual inductance variation.