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Underwater wireless power transfer (WPT) has gained a lot of popularity in recent years. In the seawater environment, the electrical conductivity is non-negligible compared with that in the air. Therefore, the eddy current loss is generated by the high-frequency alternating currents in the coils. The eddy current loss of the aligned coils has been analyzed while the eddy current loss of the misaligned coils has not been explored yet, which is crucial because misaligned coils are more common in practical applications. In this paper, an analytical model for the eddy current loss of a coreless WPT system in the seawater with misalignments is established with Maxwell’s equations. The theoretical expressions of the electric field intensity and the eddy current loss are derived. Then the eddy current loss is analyzed under different misalignments and frequencies. It is found that the efficiency in the seawater remains stable at a frequency range of 215.5 kHz to 248.4 kHz. Moreover, the efficiency is relatively unchanged under a small lateral misalignment and decreases sharply when the lateral misalignment keeps growing. An underwater WPT prototype is built and the experiments verify the theoretical analysis.

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How to reduce the cogging torque of the integrated propeller motor is an important means to improve its noise performance because cogging torque is one of the key factors causing torque ripple. We proposed a method to reduce the cogging torque by optimizing the size of the Halbach array’s auxiliary pole. First, an analytical model for the airgap magnetic field of Halbach array based on different dimensions (including the circumference ratio and the radial thickness) of the auxiliary pole is given. Then the finite element method is used to verify the analytical model. On the basis, we calculated the cogging torque of different size of auxiliary poles as sample data by combining different circumference ratio and radial thickness. Furthermore, using the two-variable single-objective neural network genetic optimization algorithm based on Backpropagation (BP), we obtain the optimal size of the auxiliary pole. Finally, comparing the motor cogging torque and torque ripple before and after optimization indicated that the cogging torque and torque ripple are effectively reduced after optimizing the size of the auxiliary pole.

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