In this paper, transient current and voltage responses, caused by low and high impedance faults in a power system with distributed generation (DG) systems, are investigated. The proposed approach utilizes a novel transient index (TI) based on the voltage during fault at the point of common coupling. The proposed technique uses voltage signals at DG connection point to provide the value of TI. The performance of the proposed scheme is evaluated on a power system consisting of photovoltaic systems and wind turbine generators as the case study by using a real-time simulator. The simulation results, which will be included in the full paper, show the fast and reliable operation of the proposed fault detection technique as compared to the existing fault detection methods, not only for low impedance transient faults but also for high impedance faults.

In this paper, a control scheme is proposed to compensate nonlinear and unbalanced loads currents and mitigate neutral current in a weak distribution network utilizing a four-leg converter. Two separate Complex Coefficient-Filters (CCF) have been used to extract the fundamental frequency positive sequence component of the load current and the converter to compensate for and control the dc-link voltage. Also, due to the presence of unbalance and harmonics the voltage of the weak grid, a CCFbased Phase Locked Loop (PLL) has been used for proper synchronization with grid voltage. Owing to absence of a low-pass filter in the CCF structure does not reduce the system dynamics and increases the speed and accuracy of estimation of the frequency and phase angle of the grid voltage. The Triple-CCF (TCCF) control strategy proposed in this article is compared with the same case, Triple-Reduced Order Generalized Integrator (TROGI). Simulation results show the performance and efficiency of the four-leg active filter control strategy based on TCCF.

By increasing the number of inverter-based resources, for instance wind turbines (WTs), the overall inertia of the network and the dynamic frequency and voltage stability are decreased. Proper battery energy storage system (BESS) control can improve stability in this case. In this paper, by considering a low-inertia power grid facing loss of generation, the effect of BESS on stability enhancement is evaluated. The study network is a modified Kundur's four-machine system modeled in PowerFactory. The results show that BESS can reduce fluctuations and increase the stability of the system.

A pilot protection method that uses the forward and backward voltage travelling waves to identify DC line faults is proposed in this paper. This method is based on the idea that under internal faults forward and backward travelling waves are observed at both sides of the line within a specific time period. However, under external faults and depending on their direction, backward voltage travelling wave is not observed at one of the terminals. Therefore, a transient-based criterion based on simultaneous existence of line-mode forward and backward voltage travelling waves is proposed. It is shown that the proposed protection method is able to identify internal faults at any location along the line with fault resistance up to 1000 𝛀 with fast response and high sensitivity and selectivity. Performance evaluations of the proposed protection method is performed using a bipolar MMC-HVDC transmission line, simulated in PSCAD/EMTDC. Index terms-Forward and backward travelling waves, HVDC protection, pilot protection, travelling wave protection.

This paper presents a new distributed eventtriggered control mechanism for accurate load sharing and voltage regulation in islanded AC microgrids (MGs). The control structure is composed of two layers. The primary control level coordinates the output current of the Distributed Energy Resources (DERs) by utilizing the V-I droop control strategy. In this method, all DERs are synchronized to a common rotating reference frame. To realize proportional load sharing among the DERs, for each DER, the d and q components of the output voltage are determined in accordance to droop characteristics of the d and q axis currents. To eliminate the load sharing caused by the line voltage drops, the slope of the droop characteristic of each DER is altered by means of a distributed secondary control scheme. The secondary controller utilizes an event-triggered communication strategy, which remarkably decreases the exchanged data and saves bandwidth. Simulation results show that the proposed method favors smooth dynamic performance and efficient network utilization.