Modeling and Analysis of Undersea Capacitive Power Transfer Based on Conduction Current in Seawater

The liquid environment and high conductivity of the seawater, which changes the characteristic of capacitive coupler compared to the air condition, are the difficulties to adoption of capacitive power transfer (CPT) technology for marine device. In this article, a universal circuit model of the bipolar plate fully immersed into water environment is proposed and divided into three cases based on the conductivity, validating the conduction path dominates the capacitive coupling in seawater. Then, the theoretical model of undersea four-plates coupler immersed into seawater, which consists of four coupling capacitances between metal plate and seawater and six seawater resistances, is derived, analyzed, and simulated. It well explains the reason of stable parameters of the coupler and power mainly flowing in receiving side since coupling object is seawater rather than plate. Later, a seawater CPT system with Y-type capacitor and single wire is proposed for realizing efficient power transmission. Finally, a laboratory prototype is established and achieves stable 171 W and 85% dc-dc efficiency with lower than 1% variation under random misalignment.