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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 two anti-interference adaptive single-phase auto-reclosing (ASPAR) schemes for transmission lines with shunt reactors. This approach is based on faulty phase reactive power characteristics. Instantaneous power algorithm (IPA) is used to calculate the reactive power using voltage and current measurements at only one end of the transmission line. After fault extinction, faulty phase reactive power magnitude rapidly rises and can be divided into five frequency components, hence, magnitude and frequency components ratio are used to identify fault extinction time. Integral processes are included in IPA, for this reason, the proposed ASPAR schemes possess anti-interference capability, and it can be used on wind power outgoing lines with multiple kind of interference often. The proposed approach considers various transmission lines interferences: rapid transmit power fluctuation and external lightning strike. Influences of high frequency disturbance and wind power plants low voltage ride through (LVRT) process were also taken into account. The proposed ASPAR schemes is extensively investigated on a typical wind power outgoing line, Hami, Xinjiang, China via the simulation platform PSCAD/EMTDC 4.5.0.0. Different cases are studied considering rapid transmit power fluctuation and external lightning strike. The simulation results ensure the validity and feasibility of the proposed ASPAR schemes on transmission lines with and without much interference. Besides, the robustness of the proposed ASPAR schemes against varied fault location and transition resistance is also verified.

This paper proposes a protection method for single line-to-ground (SLG) faults in an ungrounded offshore wind farm with fully-rated converter-based wind turbines. The proposed method uses the unsynchronized current phasors measured by unit protections installed at the connection point of the fully-rated converter (FRC)-based wind turbines (WTs). Each unit protection collects the unsynchronized current phasors from two adjacent nodes and synchronizes them by aligning the positive-sequence current to the same phase angle. The faulted section is identified by comparing the phase angles of the synchronized zero-sequence currents from adjacent nodes. Simulations of an ungrounded offshore wind farm with relay models were carried out using power system computer-aided design (PSCAD)/ electromagnetic transients including direct current (EMTDC).

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).