A Cutting-Edge Device for DC Fault Isolation and Enhanced AC/DC Fault Ride-Through for MTDC Systems—PART I: Topology and Principle

In the flexible multiterminal dc (MTDC) transmission systems, during dc short-circuit faults on the dc overhead line (OHL) and ac short-circuit faults on the ac network of the grid-side converter, dc circuit breakers (DCCBs) and dc choppers are reliable solutions to handle faults, as they ensure uninterrupted operation. However, their high costs challenge their widespread applicability. In this two-part paper, a device with high performance and low cost is proposed. Part I describes the principles of handling ac and dc short-circuit faults, and provides a theoretical analysis of the performance of dc fault isolation (DC FI) and ac/dc fault ride-through (AC/DC FRT). In Part II, the feasibility of the proposed device is validated on a four-terminal MTDC simulation system and a scaled-down hardware experimental platform. The performances and cost-effectiveness of the proposed device with the optimal configuration are compared with those of representative DCCB and dc chopper schemes. The theoretical analysis, simulation/experiment verification, and comparison showcase the potential of the device for enhancing the cost-effectiveness of MTDC systems.