Flexible Constant-Power Range Extension of Self-Oscillating System for Wireless In-Flight Charging of Drones

The special challenge for drone wireless in-flight charging is to keep a constant charging power with a large air gap under the variation of mutual inductance and the limited payload of pickup. To solve the issue, this article proposes a flexible constant-power (CP) range extension scheme with the self-oscillating wireless power transfer system, which is achieved on the primary side. By changing the duty cycle, the proposed autonomous on–off keying modulation (AOKM) scheme can effectively expand and regulate the CP region with high flexibility, avoiding the usual pickup-side-only implementation. With the AOKM scheme, the operating frequency is autonomously adjusted to keep the CP output, where only the primary current needs to be sensed without the dc–dc converter or wireless communication. Thus, it ensures the lightweight pickup of drones. The experimental results verify that the transfer distance of the CP region can be extended by 62.4%, while keeping a constant power of 73.8 W and efficiency of 88.3% regardless of the changed air gap and misalignment. Hence, based on the proposed flexible CP range extension (AOKM) scheme, the large-range CP charging region with high efficiency can be obtained for the drone wireless in-flight charging system, thus prolonging the flight time of drones.