DC fault current-limiting and isolating technique for the MMC-based DC system

DC fault isolation is the key problem in the flexible dc system. At present the dc circuit breaker which could operate fast enough with a large fault current is still unavailable. Based on the dc fault transient characteristics in the dc system based on the modular multilevel converter (MMC), a feasible isolating method was developed by improving the topology of the MMC, which limits the dc-side cable current to a lower level and then interrupts the fault circuit by a dc load switch. Comparisons between different isolating methods show the superiorities of the proposed method. Simulation tests were carried out using MATLAB/Simulink and the feasibility of the proposed isolating method was demonstrated.