Frequency selection for underwater wireless power transfer based on the analysis of eddy current loss

Wireless power transfer (WPT) technology is ideal for wireless charging of unmanned underwater vehicles (UUV). However, in underwater WPT systems, the eddy current loss (ECL) caused by the conductivity of seawater cannot be ignored. This paper obtains the expressions of the equivalent ECL resistance and mutual inductance by calculating the complex power generated by the current in the electric field. An intuitive circuit model is used to describe ECL and its superposition effect. Based on the system efficiency expressions, the influence of the medium conductivity, coil gap and operating frequency on the transmission efficiency is analyzed. Results show that there is an optimal frequency to achieve the maximum dc-dc efficiency in the seawater. Simulated and experimental results verify the validity of the method in calculating ECL and capturing the optimal transmission frequency.