Research on Energy and Efficiency Drop Issue of Underwater Wireless Power Transfer Systems

Underwater wireless power transfer (UWPT) technology provides a feasible way to solve the problems of poor safety, low lifespan, and complex maintenance of the traditional plug-and-play charging method for unmanned underwater equipment because it can realize energy supply in the sea through non-electrical contact. However, the UWPT system faces more challenges than land-based wireless power transfer (WPT) due to the complex marine environment. Currently, UWPT systems based on magnetically coupled resonance technology suffer significant power and efficiency drops in real project applications compared to air environments. Although it is believed to be due to the difference in electrical parameters between the marine environment and air, few studies have analyzed and investigated the mechanism of this problem. In this paper, the additional eddy current loss and resonance drift problems that affect the energy efficiency of UWPT systems are investigated and analyzed. Furthermore, the design method of UWPT frequency optimization and the on-line and off-line compensation correction methods of system topology are proposed. Finally, the influence mechanism of the seawater medium and the correction effect of the design method are verified by experiments. Prominently, the proposed pre-compensation methods and calibration ideas are conducive to advancing the energy efficiency improvement, reliability, and commercialization and engineering progress of UWPT technology.