Six-Plate and Hybrid-Dielectric Capacitive Coupler for Underwater Wireless Power Transfer

This article presents a novel design approach for a six-plate horizontal coupler for underwater capacitive power transfer (CPT). The coupler comprises four power transfer plates and two shielding plates that effectively prevent external interference and reduce its potential as an interference source. Unlike prior six-plate CPT coupler designs, this approach employs different dielectric materials between the plates. Specifically, water acts as the dielectric between the transmitting/receiving side plates, whereas air is used between the same-side power transfer plates and shielding plates. This selection of materials significantly reduces the ratio of self-capacitance to mutual capacitance due to the high permittivity of water as compared to air. Consequently, the coupling coefficient of the six-plate coupler is enhanced, leading to increased efficiency while maintaining electric field shielding. Experimental results from a 5-kW prototype with 200-mm side length plates and 10-mm air layer thickness demonstrated a dc-dc efficiency of 87.2% over a 60 mm distance in freshwater testing. Additionally, the coupler demonstrated relative insensitivity to misalignment, with the efficiency remaining at 84.3% when offset by 50 mm and 81.4% for a transfer distance increase to 100 mm. These findings highlight the potential for this novel design to be utilized in challenging underwater transfer scenarios.