Analysis of Eddy Current Loss and Efficiency Optimization for Bidirectional Underwater Wireless Power Transfer of AUVs
Liu Yuxin, Gao Fei, Liu Xin, Cheng Zhengshun, Liu Dong
1. School of Electronic Information and Electrical Engineering Shanghai Jiao Tong University Shanghai 200240 China; 2. School of Naval Architecture Ocean and Civil Engineering Shanghai Jiao Tong University Shanghai 200240 China
Abstract：Wireless power transfer (WPT) has been widely applied in autonomous underwater vehicles (AUVs), effectively addressing the issues related to limited endurance, challenging plug-and-charge processes, and leakage in seawater. Compared with the WPT in air, the eddy current loss (ECL) in seawater significantly decreases the efficiency. Recently, some methods have been proposed to reduce the effect of ECL, such as modifying coil structures and adjusting operating frequency, which complicates the system design. This paper proposes an underwater bidirectional LCC WPT system with a phase-shifting strategy for the primary and secondary inverters. The ECL is reduced by increasing the phase angles between the inverter voltages on both primary and secondary sides, thereby increasing overall efficiency. With fixed coil parameters, the amplitude of the induced electric field excited by each coil current in seawater is directly proportional to the current amplitude, while the phase angle of the induced electric field at any point between the two coils is almost the same. The synthetic induced electric field is the vector sum of the induced electric field generated by each coil current. Thus, the phase angle of the synthetic-induced electric field is primarily determined by the phase angle of the coil current. Consequently, increasing the phase angle between the coil currents decreases the amplitude of the synthetic-induced electric field, leading to a decrease in ECL and an increase in efficiency. When the system reaches the maximum efficiency, the decrease rate in ECL equals the increase rate in other circuit losses. To achieve zero voltage switching (ZVS) for both side inverters, the phase angle between the two inverter voltages varies from 90° to 180°. A prototype of a 200 V/3.5 kW underwater bidirectional LCC WPT system is built. Waveforms of inverter voltages, inverter currents, and coil currents are shown with phase angles of 100° and 120°. Increasing the phase angle of inverter voltages raises the phase angle of coil currents. Meanwhile, the near-constant coil current amplitude is maintained, and the amplitude of the synthetic induced electric field is reduced. The inverter current distorts as the phase angles of the inverter voltages increase. The system efficiency is tested in air and seawater. Experimental results show that the maximum efficiency can be achieved in air at a phase angle of 92.6° with a maximum efficiency of 94.2%. In seawater, the maximum efficiency is achieved at a phase angle of 116° with a maximum efficiency of 91.5%. Compared with the system without the phase-shifting strategy, the overall efficiency increases by 0.8% in seawater. The following conclusions can be drawn. (1) The overall efficiency can be optimized by adjusting phase angles between the two inverter voltages. (2) The maximum efficiency occurs when the ECL reduction rate equals the rate of the circuit power loss increment. Experimental results confirm that the proposed phase-shifting strategy can effectively reduce eddy current losses for the WPT in seawater, increasing the overall system efficiency.
刘宇鑫, 高飞, 刘鑫, 程正顺, 刘东. 深海无人航行器双向无线充电系统的涡流损耗分析与效率优化[J]. 电工技术学报, 2024, 39(18): 5599-5609.
Liu Yuxin, Gao Fei, Liu Xin, Cheng Zhengshun, Liu Dong. Analysis of Eddy Current Loss and Efficiency Optimization for Bidirectional Underwater Wireless Power Transfer of AUVs. Transactions of China Electrotechnical Society, 2024, 39(18): 5599-5609.
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2024, Vol. 39 
