A Novel Current-Commutation-Based FCL for the Flexible DC Grid

In the flexible dc grid, the dc fault propagates extremely fast. It requires the dc protection and the dc circuit breaker (DCCB) can identify and isolate the fault line very quickly, for the healthy network ride-through, especially in the multi-terminal dc grids. However, the existing protection and DCCB techniques for flexible dc grid can still not match the dc fault propagation speed. Therefore, a novel current-commutation-based fault current limiter (FCL) is proposed in this paper. It can limit the dc fault current effectively, to guarantee the converter continuous operation and healthy network ride-through after dc faults, so the requirement on the protection and DCCB acting speed can be decreased. Compared with the existing fault current limiting methods, the proposed FCL has tiny negative influence on the system transient response speed, operation stability, and DCCB isolating speed. The experiment tests and simulation case studies are carried out to verify the working principle and superiorities of the proposed novel FCL.
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