Modeling and Output Control of an Improved Separated Four‐Plate Undersea CPT System Considering High Conductivity Impacts

ABSTRACT Traditional capacitive power transfer (CPT) systems in air or fresh water rely on electric field coupling between plates. However, in seawater with a conductivity of 4 S/m, the high conductivity creates low‐impedance conductive paths between any two plates, fundamentally altering the coupling mechanism and making effective power transfer extremely difficult. To address this issue, this paper proposes a CPT system with a physically separated seawater medium. This structure eliminates the detrimental self‐coupling between plates on the same side, enabling efficient power transfer through the seawater. An improved circuit model is developed and validated against the conventional four‐plate structure using finite‐element simulations. To satisfy the constant‐current (CC) and constant‐voltage (CV) charging requirements of lithium batteries, a parameter optimization method based on the differential evolution algorithm is proposed to determine the optimal compensation network values. A frequency‐switching control strategy is then employed to achieve a smooth transition between CC and CV modes. A laboratory prototype is constructed with a 250 mm transfer distance in seawater. Experimental results demonstrate 153 W power transfer and 80% DC‐to‐DC efficiency at 185 kHz (CC mode) and 175 kHz (CV mode). The system achieves rapid and smooth CC/CV transitions with a maximum output error of 3.45% over the designed load range (25–100 Ω).