# Array Design and Transmitter Coils Selection for Underwater Wireless Power Transfer System
## 1 Introduction
To address the challenge posed by spatial displacement between transmitting (TX) and receiving (RX) coils induced by hydrodynamic disturbances, an adaptive power regulation strategy utilizing primary-side current feedback has been developed as detailed in reference [6]. The proposed approach dynamically adjusts the duty cycle of switch tube triggering pulses in the inverter circuit through real-time monitoring of transmission-side current parameters. This control mechanism significantly enhances the system's resilience to positional deviations while maintaining operational stability. Experimental validation demonstrates that the optimized control algorithm sustains peak power transfer efficiency across varying inter-coil gaps, confirming its effectiveness in mitigating fluid-induced misalignment effects. Aiming at the problem that the offset of the coupling mechanism affects its mutual inductance. In [7], a novel solenoid coil is proposed, thereby enhancing the average mutual inductance of the WPT system. The experimental results demonstrate a significant reduction in mutual inductance fluctuations within the system compared to conventional methods. The receiver control is mainly used in the rectifier circuit and DC chopper circuit, and the anti-offset performance of the system is improved by means of frequency conversion phase shift and duty cycle control [8; 9]. Aiming at the problem of the coupling coefficient change. In [10], a series compensation topology and control strategy with bilateral power control is proposed. The efficiency of the system is improved by controlling the switching tube of the rectifier circuit through voltage, current, and other parameters. In [11], a novel control strategy is proposed to enhance the dynamic response of UWPT systems. The study employs a switched-capacitor DC-DC converter topology integrated with a nonlinear one-cycle control method. This innovative approach effectively compensates for power fluctuations caused by lateral misalignment between the transmitting and receiving coils. In summary, the control optimization method can also improve the anti-offset performance of the underwater wireless power transfer system. However, this method also has some drawbacks. It is limited by the difficulty of communication in the underwater environment. The transmitter and the receiver cannot establish information interaction. The control strategy is mostly limited to unilateral control, and the method does not improve the anti-offset performance of the system. The controllable offset range is small, so the current method plays a more auxiliary role. The coupling mechanism optimization method is the main method to improve the anti-offset performance of the underwater wireless power transfer system. The optimization method is mainly divided into two types: coil structure optimization [12] and coil array optimization [13]. The optimization of the coil structure is mainly used for single-to-single coil power supply. Through the structural design of the coupling mechanism, the docking between the transmitting end and the receiving end is realized, and the coupling mechanism can be used to form interlockment to improve the anti-offset performance of the system. However, the structural design of the coupling mechanism using this method is more complex and the external influence factors increase. At present, there are few studies on coil array optimization, mainly using multiple transmitting coils to expand the charging area to improve the anti-offset range of the system. In order to improve the transmission performance of the system and reduce the power loss, it is necessary to design the coil switching control strategy and select the optimal power supply coil. Coil structure optimization refers to the optimized design of the transmitter coil and the receiver coil, so that it has stronger anti-offset performance [13; 14; 15; 16; 17]. In [18], a conical electromagnetic coupling mechanism with good offset tolerance and transmission efficiency in an underwater environment was proposed.