A Lightweight and Robust Drone MHz WPT System via Novel Coil Design and Impedance Matching

This article proposes a comprehensive approach to address the challenges posed by the simultaneously varying dc load and coil coupling in drone wireless charging, which inevitably occur during battery charging and landing positioning. The combination of two new coil designs, a quasi-elliptic transmitting (Tx) coil and a “belt” receiving (Rx) coil, enables adequate power transfer at megahertz (e.g., 6.78 MHz) and over a large circular landing area. The on-board “belt” Rx coil (5.8 g) especially helps achieve lightweight and minimize air resistance. A load-pull-based impedance analysis is then performed to clarify the need for an impedance matching network (IMN) on both Rx and Tx sides (i.e., Rx-IMN and Tx-IMN). A new Rx-IMN explicit design is specially developed to significantly limit the range of variation in the coupling coil input impedance, thereby helping to simplify the design of the Tx-IMN to ensure an efficient power amplifier operation. With the proposed coil and IMN designs, actual drone wireless charging experiments demonstrated improved system dc-dc efficiency (max. 83.5%) and dc-dc voltage ratio stability at three representative landing positions (i.e., minimum, medium, and maximum coil coupling).