Magnetic Structure Design of Wireless Power Transfer for Free-Rotating UAV With Low Stray Magnetic Fields

Rotor-unmanned aerial vehicle (UAV) wireless charging systems require low stray magnetic field distribution characteristics. This article proposes a bipolar four-coil structure and a four-solenoid receiving structure for the UAV wireless charging system. Specifically, employing Biot–Savart’s law, the microelements of the coil are decomposed to ascertain that a four-coil distribution can generate a horizontal magnetic field while maintaining lower stray magnetic field distribution characteristics. The optimal winding connection scheme for the four-solenoid structure is also determined. The finite element analysis confirms that the proposed structure can reduce external stray magnetic field by 89% compared with the unipolar structure. A 380Wprototype is constructed, achieving a maximum transmission efficiency of 87.54%. Finally, experimental results verify the feasibility and effectiveness of the proposed magnetic coupling structure.