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The design of an effective protection system for inverter-based microgrids is a complicated engineering challenge. This is due to the fact that inverters have limited fault current capabilities, and that the conventional overcurrent protection is not suitable for inverter-based microgrids. This paper introduces a novel protection method for inverter-based microgrid using a current-only polarity comparison. The proposed method is based on the phase difference between the pre-fault and fault current components. The method responds to faults in both grid-connected and autonomous operation modes and provides a new way to identify faulted sections. Simulations of an inverter-based microgrid with a relay model are conducted using PSCAD/EMTDC software. The results show that the proposed method can detect faults in inverter-based microgrids.

This paper proposes a novel protection method for single line-to-ground (SLG) faults in ungrounded low-inertia microgrids. The proposed method includes microgrid interface protection and unit protection. The microgrid interface protection is based on the difference between the zero-sequence voltage angle and the zero-sequence current angle at the microgrid interconnection transformer for fast selection of the faulty feeder. The microgrid unit protection is based on a comparison of the three zero-sequence current phase directions at each junction point of load or distributed energy resources. Methods are also included to locate the minimum fault section. The fault section location technology operates according to the coordination of microgrid unit protection. The proposed method responds to SLG faults that may occur in both the grid and the microgrid. Simulations of an ungrounded low-inertia microgrid with a relay model were carried out using Power System Computer Aided Design (PSCAD)/Electromagnetic Transients including DC (EMTDC).