# Array Design and Transmitter Coils Selection for Underwater Wireless Power Transfer System
## 1 Introduction  
Underwater electromechanical equipment have demonstrated significant application value in the domains of marine exploration, ocean development, and hydrological monitoring. As the principal power source for underwater electromechanical systems, the mode of electric energy transmission has emerged as a critical challenge. Traditional underwater power transmission predominantly employs the wet mating technique, wherein power is conveyed via metal conductors. However, the underwater environment can induce corrosion and aging in these metal wires, thereby reducing their operational lifespan. Moreover, this wet mating interface presents several drawbacks, including complicated docking procedures, elevated costs, and a limited service life. The advent of wireless power transfer (WPT) technology presents a viable solution to address the limitations inherent in conventional energy transmission methodologies. Nevertheless, operational challenges arise when implementing this technology in aquatic environments. Due to the dynamic hydrodynamic forces exerted by water currents, submerged electromechanical systems inherently lack the positional stability characteristic of terrestrial installations. This mobility-induced instability results in misalignment of the coupling interface during subaqueous charging operations. Such spatial displacementbetween the receiver and transmitter coils directly compromises the magnetic coupling efficiency, leading to progressive deterioration of system performance metrics. Specifically, the coupling coefficient diminishes exponentially as angular deviation increases, consequently causing substantial degradation in power transfer efficiency accompanied by marked elevation in resistive power dissipation. To augment the anti-offset performance and optimize the power transfer efficiency of Underwater Wireless Power Transfer (UWPT) systems, researchers have conducted extensive investigations into three principal technical strategies. The predominant approaches currently under exploration include: (1) a capture-and-fixation methodology for positional stabilization, (2) advanced control optimization techniques for dynamic regulation, and (3) coupling structure refinement through electromagnetic field modulation. Based on distinct capture mechanisms, underwater electromechanical equipment fixation systems can be categorized into three primary configurations: capture-type [1], platform-type [2], and containment-type [3]. These methodologies employ peripheral mechanical systems to achieve stable capture and secure positioning of submerged equipment, effectively mitigating hydrodynamic disturbances and enhancing system resistance to positional deviations. The implementation of such containment strategies specifically addresses the critical challenge of positional instability in underwater wireless power transfer systems. Once the electromechanical components are securely stabilized through these mechanical interfaces, the operational environment achieves requisite stability for reliable energy transmission, thereby facilitating numerous successful engineering applications. Notwithstanding these advantages, current implementations require the development of sophisticated mechanical architectures and present technical challenges associated with precision docking operations. Based on distinct control architectures, the control optimization methodology is categorized into transmitter-side regulation and receiver-side regulation. This approach enhances the system offset suppression capability through dynamic modulation of critical operational parameters including excitation frequency, voltage levels, and current characteristics. The transmitter-side control strategy is primarily implemented in inverter topologies and compensation networks, achieving enhanced offset rejection through coordinated implementation of frequency conversion phase shifting, switched inductive elements, and adaptive capacitive elements [4; 5].