Capacitive Wireless Power Transfer Independent of Load Impedance Fluctuation with Transfer Distance

The transfer distance variation of a coupler is a significant issue for capacitive wireless power transfer (WPT). This paper presents a capacitive WPT system independent of load impedance fluctuation with the transfer distance for underwater drones operating in freshwater. A capacitive coupler with opposite feeding is the primary design element. Maximum efficiency and stable power transmission are provided that a phase difference between the feeding point and the coupler electrode edge becomes π/2, and an unloaded Q-factor of surrounded dielectric is large, such as freshwater. Furthermore, the constant-current output inverter suppresses input power to the coupler at a distance where the efficiency drops, automatically reducing electricity waste. Finally, their prototypes are demonstrated at a transfer distance of 20, 50, and 100 mm in tap water.

I. Introduction

Many underwater infrastructures, such as bridges, dams, and water pipes, support our lives behind the scenes in freshwater and seawater. Although their inspections are urgently needed [1], [2], divers in charge of the inspections are continuously exposed to danger, and a lack of human resources is expected in future. Therefore, an unmanned inspection by autonomous underwater drones equipped with wireless power transfer (WPT) technology has been proposed, as shown in Fig. 1. When the battery gets low due to the inspection, the underwater drone lands at a nearby charging station and receives the power and sends the inspected data. The WPT system can be built without additional power transmission and distribution networks using clean energy, including wind and solar power.