Adaptive Current-Angle-Based Phase Selection for Microgrids With Inverter-Interfaced Renewable Energy Sources

Renewable energy sources (RESs) possess different fault signatures as compared to the traditional synchronous generators, thus introducing new challenges for microgrid protection. Among these challenges is phase selection, which is a prerequisite for selective phase tripping (SPT). This paper analyzes the root causes behind the failure of current-angle-based phase selection methods (PSMs) used by commercial relays in microgrids with inverter-interfaced RESs (IIRESs). Besides, the operation of the recently-developed voltage-angle-based PSM is investigated to unveil its points of strength and weakness. Then, adaptive zoning for the current-angle-based PSM is proposed to cope with the unconventional IIRES fault current signatures and enable precise SPT. As a result, microgrid reliability and resiliency during faults are enhanced. The proposed PSM depends on local measurements to update the PSM zones online by estimating the angles between the sequence impedances behind a relay. Comprehensive time-domain simulations verify the effectiveness of the proposed PSM at various fault resistances, fault locations, and microgrid topologies.