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

The special challenge for drone wireless inflight 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 paper proposes a flexible constant-power (CP) range extension scheme with the self-oscillating wireless power transfer (WPT) 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 73.8W 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