Wireless charging to autonomous underwater vehicle effectively prolongs the attended time and extends the endurance mileage. As the most promising underwater power feeding technique, inductive power transfer is also faced with challenges like the attenuation in seawater, ocean current disturbance etc. Special concerns in terms of power quality, efficiency improvement and mechanical fixing need to be considered when designing the underwater electromagnetic coupling structure. An attenuation model in seawater is established in this paper. The optimal working frequency range is refined for a specific transmission media. Different from the wireless power transfer system in the air, the underwater WPT system features tight coupling between the transmitter and receiver. The optimal range of coupling coefficient needs to be re-designed, as high coupling coefficient incurs frequency splitting and the increase of harmonic component, while low coupling coefficient results in low efficiency. Based on the theoretical analysis, a self-latching coupling structure is proposed with lightweight design on receiver side. System parameters are optimized correspondingly and a 3kW experiment validates the theoretical analysis.

An inductively coupled wireless power transfer system is proposed in this paper, which is designed to comply with the battery’s load characteristics. A loosely coupled transformer with high coupling coefficient is proposed. A heterogeneous compensation topology is proposed which is able to switch between constant current and constant voltage output mode according to the load resistance. The output characteristic curve agrees with the charging curve of the battery in a whole cycle. The proposed topology has a misalignment range of 300 mm where the coupling coefficient is 0.2. A 3 kW experimental platform is established to verify the theoretical analysis, and the experimental results show that the proposed loosely coupled transformer has high coupling coefficient and high power transmission efficiency (95.2% in aligned position) within a large misalignment range, which agrees with the charging scenario of the electric vehicle.

The application of wireless power transfer technology in the underwater environment proposes both opportunities and challenges to undersea power feeding. Due to the attenuation of electromagnetic waves in seawater, the distance between transmitter and receiver is always maintained at a minimum value, which results in tight coupling between the transmitter and receiver. The tight coupling condition provides a low impedance loop for high-order harmonic, so the component of the harmonic wave is thus significantly increased and cannot be ignored in the power transmission system. In order to fully utilize the harmonic energy, a fundamental-harmonic dual-channel system was proposed and studied in this paper. Compared with single-channel systems transmitting fundamental wave only, the dual-channel system has higher power transmission capability, while the loss in dual channel system can be less than that of a single-channel system after proper optimization. A 3 kW experiment platform is established to verify the effectiveness of theoretical analysis.