Frequency Optimization Method for Underwater Wireless Power Transfer Considering Coupling Conditions

Due to the high conductivity of the seawater, the eddy current loss (ECL) increases with the rising frequency of underwater wireless power transfer (WPT) systems. Moreover, The ECL is dependent on the coupling conditions of the system. The optimum frequency will be shifted when the coupling condition is changed. Thus, it is essential to analyze the optimal operating frequency of underwater WPT systems considering coupling conditions. This digest proposes a three-coil coupling circuit model to describe the underwater WPT system. By introducing the equivalent ECL impedance at primary and secondary sides, the expressions of ECL against frequency and coupling conditions are derived. Then, the optimal frequency for the highest efficiency is derived based on the model. It is concluded that a higher coupling coefficient leads to the increment of optimal frequency. A 1-kW underwater WPT prototype was built to verify the theoretical analysis.