Assessment of appropriate SFCL type considering DC fault interruption in full bridge modular multilevel converter HVDC system

The modular multilevel converter (MMC) is the most promising converter topology for implementations of voltage source converter (VSC) high-voltage direct-current (HVDC) grid. Existing research has focused on operational characteristics and improvement of efficiency by optimizing the control. Among various MMC topologies, a full bridge (FB) sub-module (SM) MMC with fault interruption capability has attracted attention because it does not require a dc circuit breaker. However, the most severe faults on dc line, can cause steeply rising fault currents with high peak magnitude, but there is a lack of literature regarding fault current reduction in FB-MMC systems. This problem can be overcome by applying the fault current limiter (FCL) and the superconducting fault current limiters (SFCLs), which have already been developed for the ac grid, have been considered in this paper. We have verified the applicability of two well-known SFCL types i.e., resistive SFCL (R-SFCL) and saturated iron core type SFCL (SIC-SFCL) in FB-MMC grid. Current limiting characteristics and energy dissipation has been according to the location of fault on dc line has been studied. We compared the merits and demerits of the aforementioned SFCLs based on the simulation results. The results indicate, SIC-SFCL to be the most suitable fault current limiter for FB-MMC HVDC system application. (C) 2001 Elsevier Science. All rights reserved