A protection strategy for inverter-interfaced islanded microgrids with looped configuration

Development of an efficient protection strategy is one of the main barriers in paving the way for the implementation of inverter-based microgrids. The limited fault current of voltage-sourced converter (VSC) units as the sole fault feeding sources in the islanded mode of operation makes the fault detection difficult for conventional overcurrent-based protection system. On the other hand, bidirectional power flow due to the presence of distributed energy resource units and looped configuration of microgrids results in miscoordination of the overcurrent relays. To address these problems, this paper proposes a protection strategy for islanded inverter-interfaced looped microgrids. By monitoring the fault-imposed component of VSC current, the proposed scheme quantifies the severity of fault condition as the fault detection criterion. To preserve the protection coordination among available overcurrent relays, the proposed protection scheme adaptively changes the limiting level of hybrid reference frame limiter of the VSC control system proportional to their distances to the fault point. The proposed protection scheme is local, and there is no need for any change in the commercially available overcurrent protection relays. The reliable performance of the proposed protection strategy is assessed on the simulation model of a looped microgrid network.