An Underwater Hybrid Wireless Power Transfer System With Constant Power Output Against Misalignment

To address the instability of power output in underwater wireless power supply devices under coupling misalignment, this paper proposes an underwater hybrid wireless power transfer (UHWPT) system with constant power output against misalignment. The energy transfer structure of the system is an integrated magnetic-electric coupler, which consists of double- D coils and C-shaped plates. The concave ferrite is attached to the backside to enhance magnetic coupling strength and reduce eddy current loss induced by leakage flux within the plate. To facilitate constant current/constant voltage (CC/CV) mode switching for underwater equipment batteries, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S/LCL</i>-<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> compensation network is designed, enabling simple switching control. Both CC and CV modes exhibit constant power output characteristics with high misalignment tolerance. The operating principle of the proposed UHWPT system is analyzed in detail, and the power fluctuation factor <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α</i> considering mutual inductance and mutual capacitance as well as the zero-phase angle (ZPA) condition of the system are derived using the fundamental harmonic approximation (FHA). A system design method with high misalignment tolerance based on parameter <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α</i> is proposed and validated through a field-circuit coupling model. Finally, an experimental prototype is developed, and the results demonstrate that the system achieves load-independent constant current and constant voltage outputs, with a maximum DC-DC efficiency of 88.2% when the input power is 255 W. And the output power variations in both CC and CV modes remain within 15% under 50% horizontal misalignment.