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The increasingly popular inverter distributed generation in microgrids is leading to changes in system fault characteristics. The fault behaviors of inverter distributed generation are closely related to the control mode. Here, a photovoltaic power supply in constant power mode enters a low-voltage ride-through state when there is a fault in the microgrid. The output current phase in the ride-through state is analyzed, and a local protection method based on the phase difference of the feeder positive-sequence current is proposed. The method is used to avoid interpreting voltage surges as faults, and to detect and locate faults rapidly and accurately. Electromagnetic transient simulation software is used to demonstrate the efficacy of the proposed protection scheme.

High-resistance faults in direct current (DC) microgrids are small and thus difficult to detect. Such faults may be “invisible” in that grid operation continues for a considerable time, which damages the grid. It is essential to detect and remove high-resistance faults; we present a detection method herein. First, the transient DC current during the fault is subjected to hierarchical wavelet decomposition to identify high-resistance faults accurately and sensitively; the wavelet coefficients are detected using the singular value decomposition (SVD) method. The SVD valve can denoise the dc microgrid fault current, which eliminates the influence of converter switching frequency and background noise effectively. Power system computer-aided design (PSCAD)/electromagnetic transients including direct current (EMTDC)-based simulations showed that our method successfully identified high-resistance faults.

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.

A Novel method for fundamental frequency estimation in power systems is presented, which has three stages. In the first stage, the input signal is decomposed into two orthogonal components by using cosine and sine filters with a variable window. In the second stage, the cosine-filtered and sine-filtered signals are squared to improve the performance of estimating the fundamental frequency. Finally, Prony analysis estimates the fundamental frequency by approximating the squared signals. The performance of the proposed method was estimated for dynamic conditions on an IEEE 5-bus system. PSCAD/EMTDC was used to generate voltage signals for a load increase case and single phase-to-ground faults. The performance evaluation showed that the proposed method accurately estimated the fundamental frequency of power system signals.