Eddy Current Loss and Detuning Effect of Seawater on Wireless Power Transfer

Due to the conductivity of the seawater, the traditional mutual inductance circuit model in the air cannot be used directly to describe wireless power transfer (WPT) systems in seawater applications. This paper proposes a modified mutual inductance circuit model of an underwater WPT system to analyze the eddy current loss (ECL) and the detuning effect caused by the seawater. The time-harmonic electromagnetic field in the seawater and the air near the coil that carries a sinusoidal alternating current is analyzed. The root-mean-square (rms) value and phase angle of the induced voltage on the secondary coil can be obtained by the integral of the electric field intensity along the coil path. By introducing the equivalent ECL impedance at both the primary and secondary sides, a modified mutual inductance circuit model of an underwater WPT system was obtained. Through adding a compensation inductance to the primary circuit, the detuned system in the seawater is turned back to be resonant at the same frequency as in the air. A seawater WPT prototype was built and the experimental results verified the theoretical analysis.