A signed correlation index-based differential protection scheme for inverter-based islanded microgrids

The different fault characteristics of the inverter-based distributed generation (IBDG) units make the protection of the inverter-based islanded microgrids (IBIMGs) a formidable task. According to IEEE Std 1547.4, the limited fault current levels associated with the IBIMGs may result in misleading decisions of the traditional protective relays during fault occurrence. In this paper, a new differential protection scheme for the IBIMGs is introduced based on the signed correlation technique. The proposed scheme is formulated based on the signs of the instantaneous phase currents at both line ends instead of the current magnitudes. In addition, a signed correlation index is defined to measure the similarity between the signs of the instantaneous phase currents at both line ends employing only a time window of half-cycle. Moreover, a fault detection index is introduced to discriminate the internal faults from other events. In order to validate the proposed scheme, the 9-bus IBIMG and the modified IEEE 33-bus system are simulated on the PSCAD/EMTDC platform, and several scenarios are conducted, including load switching, outage of IBDG units, external bus faults, and internal faults. The obtained results emphasize that the proposed scheme operates correctly considering all types of faults, different fault resistances and inception angles, as well as measurement and synchronization errors.