Design and Optimization of a High Efficiency Seawater Wireless Power Transfer System with 1:1 Distance to Diameter Ratio

Seawater wireless power transfer (SWPT) technology presents an effective solution for addressing the charging requirements of underwater equipment, enabling long-term continuous operation. However, in seawater environments, the presence of eddy current loss significantly reduces efficiency as the transfer distance increases. This paper proposes a frequency optimization method for the SWPT system with a high distance-diameter ratio (HDDR) to enhance efficiency in seawater environments. Initially, the principle of eddy current loss is analyzed to establish the relationship between eddy current loss and frequency in the HDDR system, while examining the influence of different DDRs on eddy current loss. The harmonic component of the S-S compensation topology and the optimal efficiency point are derived, and a coupling structure of a multi-layer series with segmented compensation is proposed to enhance system efficiency. Furthermore, the total loss of SWPT systems of a 1:1 DDR with various sizes is analyzed. Finally, a prototype of a 5kW SWPT system with a 1:1 DDR was constructed, when seawater conductivity was 4 S/m, DC-DC efficiency reached 88.39% at DDR=1 (transmission distance 500mm), and 95.49% at DDR=0.6 (transmission distance 300mm).