Rotor-unmanned aerial vehicles (R-UAV) have structural irregularities and problems with docking offset. The traditional unipolar CP magnetic structure increases the wind resistance of the R-UAV due to its mechanical structure characteristics, which, in turn, affects the flight stability of the R-UAV. At the same time, the asymmetric characteristics of the original secondary side can generate high stray magnetic fields, affecting the stable operation of the R-UAV. Therefore, applying the wireless charging system to R-UAVs is challenging. In order to build a stable wireless charging system for R-UAVs, it is necessary to conduct a targeted optimization design based on the mechanical structure of the R-UAV. This paper proposes an “I工I” magnetic structure with high anti-offset and low stray magnetic field constraints for the wireless charging system of R-UAVs and designs a multi-stage constant current-constant voltage (MCC-CV) control strategy with soft switching capability based on the characteristics of series-series (S-S) networks.

Firstly, this paper comprehensively analyzes the characteristics of series-series (S-S) networks, develops an MCC-CV control strategy for wireless charging of lithium batteries, and designs a full-bridge phase-shift soft-switching half-bridge workflow to solve the output current oscillation problem caused by the energy storage characteristics of the resonant network during the multi-stage constant current switching process. By incorporating soft switching capabilities, the system can transition smoothly between different stages of the charging process, minimizing current oscillations and ensuring a stable charging experience. Then, a three-dimensional model of the “I工I” magnetic structure is proposed and established. The transmission structure of this coupling structure is a “I工I” core, while the receiving side structure is an “I” core integrated within the landing gear of the R-UAV. Integrating the magnetic structure within the landing gear allows for zero wind resistance characteristics in wireless charging of R-UAV. Based on the low magnetic resistance characteristics of ferrite cores, the design of the “I” core is completed. Through magnetic circuit analysis and finite element simulations, the magnetic circuit shaping and low stray magnetic field characteristics of the “I” core are determined, and a passive constraint magnetic circuit shaping method for stray magnetic fields is derived. The “I” core distribution is adjusted to increase the anti-offset capability of the “I工I” magnetic structure, thereby achieving a high anti-offset wireless charging system design.

Finally, a prototype of the “I工I” magnetic structure is built. It is shown that the system can maintain a constant output current under radial offset of 100 mm and rotational offset of 360°, with only a 2% fluctuation in transmission efficiency. At the same time, the distribution characteristics of the stray magnetic field outside the launch platform are measured, and a distribution diagram of the stray magnetic field is drawn. The proposed “I工I” is lightweight and efficient.