A 5 kW Hull-Compatible Inductive Charging System With 360° Folded Spatial Unipolar Coupler for Autonomous Underwater Vehicles (AUVs)

Inductive power transfer (IPT) for autonomous underwater vehicles (AUVs) presents many advantages compared to conductive solutions that require the vessel to be recovered from water in each charging cycle. This article proposes a novel 360° folded spatial unipolar coil structure adapting to a cylinder AUV body shape, aiming at low leakage magnetic field and good rotational misalignment tolerance. The finite element analysis (FEA)-based coupler design procedure is presented, and a 5 kW WPT system is implemented with an LCC-S compensation and a strong coupling coefficient of 0.735. The implemented prototype is tested in air, fresh water, and saltwater. The system shows good rotational misalignment and retains 82.9% of well-aligned power along 360° rotation. A peak power of 5.18 kW is achieved with 96.8% dc-dc efficiency in saltwater, and the performance in freshwater and air presents an efficiency of 96.8% and 96.9%, respectively, which shows a slight impact of the medium in a strongly coupled underwater IPT system. This article is accompanied by a multimedia video material demonstrating the structure and working principle of the proposed coupler.