Reconfigurable Cascaded Coupler to Improve Efficiency and Achieve Wide Load Range for Underwater Single-Wire Power Transfer System

Underwater single-wire power transfer (USWPT) is an attractive methodology to improve the charging safety and flexibility of underwater sensors. The output power and system efficiency of the USWPT system are highly dependent on the load resistance. However, the load resistance of underwater sensors’ battery or supercapacitor varies over a wide range during the charging process. Therefore, a reconfigurable cascaded coupler (RCC) is proposed in this article to broaden the load range of USWPT systems and improve the system efficiency. Specifically, the factors affecting the power and efficiency of the USWPT system are analyzed in depth. Cascading couplers can increase the total mutual inductance and thus improve system efficiency. Different series or parallel cascading modes of couplers can change the ac equivalent resistance and broaden the load range. A RCC and its mode switching control strategy are analyzed and designed. Finally, a 51-m-length USWPT equivalent circuit prototype is constructed to verify the validity of the proposed method. Experimental results have demonstrated the effectiveness of the proposed RCC. The load resistance range is expanded to 5–200 $\boldsymbol{\Omega}$, and the load power fluctuation is less than 5 W, system dc-to-dc efficiency maintained at 31.8–51.8%. The proposal of RCC has increased the maximum efficiency of the system from 24.95 to 51.8%.