This paper presents a comprehensive review on the application and control of Flexible Alternating Current Transmission Systems (FACTS) devices in order to improve voltage stability of power grid with high share of renewable energy systems. The rise in the development of renewable energy technologies is driven by the attempts to mitigate the effects of global warming. In addition, global energy demand continues to rise as new electricity-driven systems such as electric vehicles are being developed and as remote locations are being connected to the grid. These changes in the power grid formation comes with attendant challenges which must be addressed. One of these challenges is voltage stability issues. This paper therefore explores the applications of FACTS devices for voltage stability improvement and points out the future research direction in the area of voltage stability enhancement by FACTS devices for modern power grids characterized by increasing levels of renewable energy penetration.
The increasing penetration of wind energy to the conventional power system due to the rapid growth of energy demand has led to the consideration of different wind turbine generator technologies. In fault conditions, the frequency of the power system decreases and eventually leads to speed differences between the grid and the interconnected wind generator. This can result to power system problems such as transient instability (TS). This paper focuses on enhancing the TS of a permanent magnet synchronous generator (PMSG)-based power system during 3ph fault conditions using FACTS devices. The power system considered is connected to a large wind farm which is based on PMSG. Critical clearing time (CCT) is used as an index to evaluate the transient state of the system. Under the study of an IEEE-14 bus system using PSAT as a simulation tool, the integrated CCT with PMSG-based wind turbine is improved with three independent FACTS devices. One of the synchronous generators in the test system has been replaced at random with the PMSG-based wind turbine which is meant to generate an equivalent power. Time domain simulations (TDSs) were carried out considering four study cases. Simulation results show that the (CCT) of the system with the FACTS devices is longer than the CCT without them, which is an indication of TS improvement.
<p>In deregulated electricity markets, generation companies (GENCOs) make unit commitment (UC) decisions based on a profit maximization objective in what is termed profit based unit commitment (PBUC). PBUC is done for the GENCOs demand which is a summation of its bilateral demand and allocations from the spot energy market. While the bilateral demand is known, allocations from the spot energy market depend on the GENCOs bidding strategy. A GENCO thus requires an optimal bidding strategy (OBS) which when combined with a PBUC approach would maximize operating profits. In this paper, a solution of the combined OBS-PBUC problem is presented. An evolutionary particle swarm optimization (EPSO) algorithm is implemented for solving the optimization problem. Simulation results carried out for a test power system with GENCOs of differing market strengths show that the optimal bidding strategy depends on the GENCOs market power. Larger GENCOs with significant market power would typically bid higher to raise market clearing prices while smaller GENCOs would typically bid lower to capture a larger portion of the spot market demand. It is also illustrated that the proposed EPSO algorithm has a better performance in terms of solution quality than the classical PSO algorithm.</p>
This paper investigates the application of large-scale solar photovoltaic (SPV) system for voltage stability improvement of weak national grids. Large-scale SPV integration has been investigated on the Nigerian power system to enhance voltage stability and as a viable alternative to the aged shunt reactors currently being used in the Nigerian national grid to mitigate overvoltage issues in Northern Nigeria. Two scenarios of increasing SPV penetration level (PL) are investigated in this work, namely, centralized large-scale SPV at the critical bus and dispersed large-scale SPV across the weak buses. The voltage stability of the system is evaluated using the active power margin (APM) also called megawatt margin (MWM) derived from Active Power–Voltage (P–V) analysis, the reactive power margin (RPM) and the associated critical voltage–reactive power ratio (CVQR) index obtained from Reactive Power–Voltage (Q–V) analysis. All simulations are carried out in DIgSILENT PowerFactory software and result analyses done with MATLAB. The results show that with centralized SPV generation for the case study system, the highest bus voltage is able to fall within acceptable limits at 26.29% (1000 MW), while the dispersed SPV achieves this at 21.44% (800 MW). Also, the dispersed SPV scenario provides better voltage stability improvement for the system as indicated by the MWM, RPM and the CVQR index of the system. Therefore, this work provides a baseline insight on the potential application of large-scale SPV in weak grids such as the Nigerian case to address the voltage stability problems in the power system while utilizing the abundant solar resource to meet the increasing energy demand.
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