A novel control approach for protection of multi-terminal VSC based HVDC transmission system against DC faults

Overall performance of the voltage source converters (VSCs) has improved during the recent years. Improvement of the VSCs along with the attractive features of the VSC based high voltage direct current (HVDC) transmission systems over the thyristor based HVDC transmission systems make it possible to build multiterminal (MT) VSC HVDC transmission systems. However, the VSCs are vulnerable against dc side faults and a method needs to be employed to extinguish the dc fault current. In this paper, three different configurations of solid state dc circuit breakers (CB) for protection purposes are studied. Moreover, a new control method to protect the VSCs against the dc side fault is proposed, the new method makes it possible to extinguish the dc fault current with the existing ac breakers on the ac side or with the lower rating solid state (SS) DCCBs. The performance of the SS DCCBs and the proposed method are studied using Real Time Digital Simulator (RTDS).