Half-bridge modular multilevel-based HVDC converters with external pre-charged capacitors for dc fault current suppression capability

Half-Bridge Modular Multilevel Converters (HB-MMCs) are defenseless against DC side faults. Different types of DC Circuit Breakers (DCCBs) assisted with arrester banks/damping resistors such as solid-state CBs and hybrid DCCBs can be used to interrupt the DC fault current. Arrester banks are used to block any overvoltage after interrupting the fault current and in turn to demagnetize the circuit inductors. The main disadvantage of the arresters is that they forcibly break apart when they are overloaded. In this work, an arrester-less DC fault current limiter is proposed for HB-MMC configuration. The proposed DC fault current limiter has two pre-charged capacitors in series with transmission poles. These pre-charged capacitors are bypassed during normal conditions, while they are inserted in the DC current path during DC side fault to limit the grid current contribution into the dc fault. The proposed protection scheme is assessed using a simulation study.