Backup protection with accelerating strategy based on fault control of modular multilevel converters in medium‐voltage direct current distribution network

Abstract

AbstractThe medium‐voltage DC distribution network with multiple DC feeders is more cost‐effective when equipped with switches than DC circuit breakers. Under such conditions, the converters with fault‐handling capacity are blocked to clear the fault, which will cause the rapid disappearance of the fault current. Therefore, the primary protection has to pursue high speed at the expense of reliability, which threatens the network's safety. To construct a reliable protection system, backup protection with an accelerating strategy based on the fault control of converters is proposed. The current is controlled first by the fault control of converters to ensure the fault characteristics during backup protection. Then the DC switches on the healthy line are blocked by the polarity of the current integral, and the distribution network turns into the close‐loop mode to provide a fault current path. When the DC switches on the faulty line disconnect according to the predefined time delay, the current change time is recorded and thus the switches in the network are accelerated without communication. The proposed scheme only depends on the measured local current and the backup function still exists after acceleration. The effectiveness of the proposed scheme is verified in power systems computer aided design/electromagnetic transient including DC (PSCAD/EMTDC).