Design and Misalignment Tolerance Analysis of a Nonuniform DD Coil for UAV Wireless Charging

ABSTRACT To address the rapid mutual inductance attenuation of conventional double‐D (DD) coils under lateral misalignment in wireless power transfer (WPT) systems, this paper proposes a nonuniform DD coil for unmanned aerial vehicle (UAV) wireless charging. The proposed coil maintains the basic DD topology and adopts a sparse‐center and dense‐edge winding scheme with an interturn spacing ratio of 1.65, which strengthens the magnetic field distribution in the lateral edge regions and improves mutual inductance retention under lateral misalignment. Based on an LCC‐S compensation network, the relationship between mutual inductance and system output characteristics is analyzed. Then, a comprehensive evaluation function considering mutual inductance retention and coil quality factor is established to optimize the interturn spacing ratio. Simulation results show that the proposed coil achieves better mutual inductance retention under lateral misalignment than the conventional uniformly wound DD coil, while largely preserving the longitudinal misalignment tolerance of the DD structure. A 150 W UAV wireless charging prototype is built for experimental verification. The results show that within ±30‐mm receiver‐side longitudinal misalignment, ±30‐mm lateral misalignment, and ±45° rotational misalignment, the proposed coil provides higher output stability, with a peak system efficiency of 88.66%. These results demonstrate that the nonuniform winding strategy effectively reduces coupling attenuation under lateral misalignment without additional auxiliary coils, making it suitable for lightweight UAV wireless charging applications.