Design and implementation of load-independent constant voltage output for medium-range 6.78 MHz wireless power transfer systems

This paper presents a 6.78 MHz wireless power transfer (WPT) system designed to provide load-independent constant voltage output, making it ideal for applications such as unmanned aerial vehicle (UAV) charging. The system ensures stable voltage across a wide range of load variations while maintaining zero-voltage switching (ZVS) operation. Operating with a coupling coefficient k = 0.08 and a compact receiver coil measuring 6 cm × 3 cm on the secondary side, the system demonstrates high efficiency and compactness. Theoretical analysis establishes the conditions for achieving load-independent operation, which are validated through simulations and experimental results. The prototype achieves a stable output voltage and consistent ZVS performance under dynamic load conditions, addressing key challenges in WPT for UAVs and other applications with variable loads. Experimental testing of the prototype showed a measured efficiency of 80.4% at 66 W, confirming its practical feasibility.