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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.

Wind turbines (WTs) are a desirable alternative to traditional nonrenewable power resources as a result of recent environmental concerns. Some of them are fixed speed wind generator (FSWG) and have been integrated to power system by squirrel cage induction generator (SCIG). Induction machine absorbs reactive power during all operating conditions, especially at fault condition may result in severe voltage drop which can lead to generator outage. This outage disconnects a significant amount of active power and consequently leads to frequency instability. In order to prevent induction generator (IG) outages in short circuit failures, this paper investigates thyristor-controlled series capacitor (TCSC) device as a candidate solution. TCSC compensates the IG terminal voltage drop by adjusting transmission line impedance at fault condition. In the proposed method, a metaheuristic technique means that shuffled frog leaping algorithm (SFLA) has been utilized to optimize the TCSC controller gains. The proposed scheme can be applied for both SCIGs and wound rotor induction generators (WRIGs) which is another advantage of this method. Single-machine infinite bus system is considered as case study, and various operating conditions and disturbances have been considered to verify the effectiveness of the proposed method.

In recent years, distribution networks have been increasingly affected by the random nature of harmonic sources introduced by nonlinear load and renewable energy sources (RES) such as photovoltaic (PV) systems. This paper presents an approach based on Genetic Algorithm (GA) and Monte-Carlo Simulation (MCS) for the optimal planning of single-tuned passive harmonic filters (PHFs) in a distribution network. The resistance and inductance of the lines within the network are modeled by frequency dependent characteristics. The probabilistic characteristics of the load and PV system currents are also considered for optimal planning of PHFs. In our optimization model, the objective function minimizes the total PHF installation cost and the energy losses, by considering the total harmonic distortion (THD) of bus voltages and maximum capacity of PHF as constraints. The proposed method is validated by a simulation study using an unbalanced three-phase real distribution system. An advantage of this method over most of the conventional approaches is that both harmonic current magnitude and phase angle of real PV systems are taken into account. Numerical results show the applicability and effectiveness of the proposed method.

In this paper, the impact of grid-connected photovoltaic (PV) systems on voltage total harmonicdistortion (THDV) in radial distribution systems is investigated. To well present the behavior of PVsystems, both amplitude and phase angle of the harmonic current sources are considered in thesimulations. Specifically, when the current harmonic phase angle is considered, the photovoltaic andload harmonic may cancel out each other, which results in lower THDV values. It is also observed formthe simulation results that by increasing the PV penetration and nonlinear load demand, THDV mayincrease even beyond the allowed range. Therefore, an optimal passive harmonic filter (PHF) planningis also proposed for THDV mitigation and its effectiveness and applicability is tested and verified underdifferent working conditions. Optimal planning is performed considering a cost objective function whichincludes PHF cost and benefit of energy loss reduction. According to simulation result, an appropriatepassive harmonic filtering could guarantee an acceptable THDV in radial distribution and reduce energy losses.

Proper installation of rooftop photovoltaic generation in distribution networks can improve voltage profile, reduce energy losses, and enhance the reliability. But, on the other hand, some problems regarding harmonic distortion, voltage magnitude, reverse power flow, and energy losses can arise when photovoltaic penetration is increased in low voltage distribution network. Local battery energy storage system can mitigate these disadvantages and as a result, improve the system operation. For this purpose, battery energy storage system is charged when production of photovoltaic is more than consumers’ demands and discharged when consumers’ demands are increased. Since the price of battery energy storage system is high, economic, environmental, and technical objectives should be considered together for its placement and sizing. In this paper, optimal placement, sizing, and daily (24 h) charge/discharge of battery energy storage system are performed based on a cost function that includes energy arbitrage, environmental emission, energy losses, transmission access fee, as well as capital and maintenance costs of battery energy storage system. All simulations are carried out in DIgSILENT and MATLAB linked together. Results show that by using the proposed approach, overvoltage and energy losses are decreased, reverse power flow is prevented, environmental emission is reduced, and economic profit is maximized.