An SMES-Based Current-Fed Transformerless Series Voltage Restorer for DC-Load Protection

The shortage of dc protection device limits the development of dc grids. This letter proposes a novel superconducting magnetic energy storage (SMES)-based transformerless series voltage restorer (TLSVR) for dc-load protections. The proposed SMES-TLSVR is made up mainly of a bidirectional-switch-based converter and a superconducting coil, and is interfaced in the series with the dc transmission line. It has the advantages of duplex voltage compensation ability, transformerless structure, and swift compensation response, and has a wider compensation range than traditional voltage-fed transformerless dynamic voltage restorer. The topology, circuit principle, and control strategy are elaborated in this letter. Finally, a kW-class SMES prototype is carried out to verify the feasibility of the proposed SMES-TLSVR.