Omnidirectional Magnetic Resonant Extender Design for Underwater Wireless Charging System

Long-range underwater wireless power transfer (WPT) systems have great application prospects in many industrial fields. However, conventional WPT systems may suffer different kinds of technical issues in this highly unstable operation environment, such as large output decay when the transmission distance increases, and output fluctuation caused by instability of the water flows. To solve these problems, this paper proposes a novel solution to achieve an enlarged resonance range, higher efficiency, and more stable output. The LCC-S-S compensation circuit is adopted in the system with a highly stable primary current, which improves its fault tolerance ability to adapt to the unstable underwater environment. A portable omnidirectional magnetic resonant extender is designed as an intermediate device to extend the underwater transmission distance and raise the system efficiency. The specially designed structure enables it with two separate but complementary three-coil WPT systems which solves the conventional angular dead zones issue. Theoretical analysis proves that under the idealized conditions, both the magnitude and phase of the load current can be effectively maintained as absolute constant, with arbitrary water flow direction or velocity. Both circuit simulation and finite element analysis (FEA) results are presented to validate that the system is possessed with high fault tolerance. For further assessment, an experimental prototype is established, and the practical test results confirm that the system can maintain a relatively high transmission efficiency under large lateral and angular misalignments ranging from -90° to +90°.