Wireless Power Transfer System for Multiple Drones In-Flight Charging Applications Under Wide Charging Tolerance with Constant Charging Current

The wireless power transfer (WPT) for drones in-flight charging is one solution for extend operation time. However, the WPT for drones fluctuates owing to the varying mutual inductance and changes in the distance between the transmitter coil and the receiver coil during flight. This paper presents a single-transmitter, multiple-receiver, wireless in-flight charging system designed to extend the operational duration of drones. The control method leverages bifurcation phenomena to track the bifurcation frequency under various coupling-coefficient conditions. To validate the proposed method, a 470 W WPT system prototype was constructed for an in-flight survey drone. The system supports an extended-range power transfer at a maximum air gap of 150 mm. The experimental results demonstrate that the WPT system can achieve up to 82% efficiency, while maintaining a constant receiver current.