Resilience enhancement of microgrids with inverter-interfaced DGs by enabling faulty phase selection

The significant differences between the fault current signatures of inverter-interfaced distributed generators (IIDGs) and conventional synchronous generator-based sources can lead to misoperation of the existing phase selection methods that operate based on the angles of sequence currents. Consequently, a selective phase reclosing/tripping scheme cannot be applied by the protection system of a microgrid, resulting in reduced resilience during asymmetrical faults. This paper develops a dual control scheme that regulates the sequence components of an IIDG current during short-circuits such that the existing phase selection methods accurately select the faulty phase(s). The proposed scheme adds a controllable voltage source and a virtual impedance to the negative-sequence circuit of an IIDG model. These newly added components are tuned to make the sequence current angles of an IIDG during asymmetrical faults similar to those of an SG while thermal limits of inverter switches are satisfied. As a result, the protection system can trip only the faulty phase(s) and the microgrid resilience during unbalanced short-circuits is substantially improved. A comprehensive performance evaluation confirms the effectiveness of the proposed control scheme under different fault conditions.