Effective scheme to restrict nonpermanent faults by suppressing fault current in MMC-based HVDC system

For the integration of renewable resources with the national grid located hundreds of mile away, a half-bridge modular multilevel converter-based high-voltage direct current system (MMC-HVDC) is a prime aspirant. During faults at DC-link due to non-resistant approach, freewheeling diodes become rectifier bridge and start feeding DC faults. The reliability of employed setup for generation, transmission and distribution is a key concern, so is the case with MMC-HVDC to be deal with, eminently for nonpermanent faults in overhead lines. This work contemplates a protection scheme to enforce rapid fault clearance and automatic recuperation for nonpermanent faults on HVDC lines. By using anti-parallel double-thyristor switches and IGBTs with AC source, the diodes freewheeling effect is ruled out and the DC-link fault current can freely decline to zero. Thus, the DC arc is demolished naturally, and insulation restoration on short-circuit point is achieved. Moreover, by switching the anti-parallel thyristor switches on fault occurrence, the DC-link fault is converted into an AC short circuit. IGBTs installed in series with AC source stop feeding to DC faults completely. Further, AC short circuit can be cleared by turning off all thyristors. PSCAD/EMTDC have been used to simulate and validate the proposed scheme in B2B configuration.