Extended-Range Constant Current WPT for Dual-Drone Charging Using a Bifurcation Approach

Despite the increasing popularity, unmanned aerial vehicles (UAVs) are often hindered by limited battery endurance and complexities of in-flight recharging. This paper presents an extended-range wireless power transfer (WPT) system designed for simultaneous in-flight charging of dual drones. By employing a bifurcation approach, the system uses bifurcation-induced zero-phase angle (ZPA) frequencies to achieve coupling-independent current gain. This allows the system to maintain a constant battery charging current across dynamically varying coupling conditions, without the need for sensors or communication modules on the receiver drones. Finite element simulation study confirms the magnetic flux density characteristics, desired for practical operation constraints. An experimental study on a 500 W prototype demonstrates the proposed system's effectiveness. The dual-receiver configuration successfully maintains a constant 5 A charging current of each drone while extending the operational air gap range by 16.7% (from 150 mm to 175 mm) compared to single-receiver scenarios. This work presents a practical solution that mitigates misalignment and air gap variation issues to enhance UAV flight endurance, an important step for drone operations during prolonged missions.