A Capacitively-Coupled Single-Wire Earth-Return Power Tether for Aerial Platforms

Single-wire earth-return (SWER) power transfer has a long history in utility transmission applications, but recent works have appeared in the wireless power transfer community. At high frequency, an earth return is achievable without physical contact, only capacitance to the surrounding environment is necessary. This paper applies that concept to form a SWER system for tethered aerial platforms, e.g. balloons, drones, or lighter-than-air renewables. The SWER concept is especially attractive in such applications because the power tether can be simplified to a single conducting cable. The capacitive return to earth is facilitated by a quarter wavelength helical resonator, which provides significant voltage gain at its natural frequency to drive a return displacement current. An equivalent circuit suitable for design purposes is developed using the theoretical model of the helical resonator and is confirmed with a laboratory prototype. Experimental results measured on a horizontal (terrestrial) 10 m tether and a vertical (aerial) 5 m tether demonstrate 500 W power throughput with 92% efficiency.