Light-weight wireless power transfer for mid-air charging of drones

Recent developments in high frequency inductive wireless power transfer (WPT) mean that the technology has reached a point where powering small autonomous drones has become feasible. Fundamentally, drones can only carry very limited payloads and thus require light-weight WPT receiver solutions. The key to achieving light weight is operating the WPT system at high frequency: this allows both the coils and the electronics to achieve very high gravametric power densities. When operated in the MHz region, the WPT coils can be manufactured without the need for ferrite, because the low coupling factor can be offset by very high coil Q factors. To make efficient MHz power conversion circuits, wide band-gap semiconductors, including Silicon Carbide (SiC) and Gallium Nitride (GaN) have provided a step change. For powering a drone, these devices are integrated into soft-switching resonant inverter and rectifier topologies and are able to operate efficiently at tens of MHz and hundreds of watts. In addition, recently discovered designs that make these inverters tolerant to load variations and have inherent voltage or current regulation features enable an WPT system to operate effectively as the separation distance and alignment between transmitter and receiver changes, which is critical when charging a flying drone. It will be shown that combining all these individual developments has enabled the charging of a 10 W micro-drone whilst hovering in the vicinity of a charging pad.