This paper investigates the application of flexible AC transmission systems (FACTS) Controllers to extend voltage stability margin in electric power systems. Many voltage collapse incidents have resulted from large disturbances such as the loss of transmission or generation equipments. Therefore, in this paper the strategy for locating FACTS Controllers is based on contingency studies. A probabilistic index is defined by using modal analysis, which can be used to rank of system buses based on their contribution to voltage instability of system under possible contingencies. Then, the most suitable buses to apply remedial actions for increasing voltage stability margin in contingency conditions can be determined by choosing the most effective buses according to the ranking. The major advantage of this approach over the deterministic N-1 criterion is that it considers contingency likelihood as well as its severity. Therefore, contingencies with high probability of occurrence are more significant for locating VAR resources. The AEP 14-bus test system is used to demonstrate the proposed approach of placing shunt FACTS Controllers.

This paper concentrates on performance evaluation and comparison of conventional Controllers such as Mechanically Switched Capacitor (MSC), Load Tap Changer (LTC), Power System Stabilizer (PSS), and FACTS Controllers such as Static Var Compensator (SVC), Thyristor Controlled Series Capacitor Power Oscillation Damper (TCSC POD) controller and Unified Power Flow Controller (UPFC) in mitigating chaos driven instabilities such as voltage and angle instabilities. The chaos is triggered by the nonlinearities associated with high gain fast excitation system of automatic voltage regulator (AVR) and shunt capacitors. The instability problem is explored by invoking bifurcation theory. Bifurcation diagrams of steady state as well as periodic solutions are plotted. From the bifurcation diagrams, the existence of various bifurcation points such as, Hopf Bifurcation (HBF), Saddle Node Bifurcation (SNB) and Period Doubling Bifurcation (PDB) are identified. With the use of tools of nonlinear dynamics, voltage collapse points, chaotic solutions due to period doublings and chaos divergence points are unearthed. Comprehensive comparisons of the effectiveness of the Controllers are presented from the point of view of delaying HBF, SNB and increasing the loadability limit.

Electromechanical oscillations in power systems usually exist due to incompatible conditions and disturbances in the network. Meta-heuristics using search strategy are used to find near-optimal solutions. Typically, the implementation of this approach involves the utilization of a fitness function to assess the candidate solutions. In nature-inspired metaheuristics optimization algorithms, an analogy from nature is used to generate approximate solutions for practical optimization problems. This work presents a comprehensive investigation into various nature-inspired optimization algorithms, including ant colony optimization, genetic algorithm, and bat algorithm. The primary focus of this paper is to explore their efficacy in the coordinated design of Power System Stabilizers (PSS) and Flexible Alternating Current Transmission Systems (FACTS). The objective of this coordinated design is to improve energy system stability and mitigate power system oscillations. Finally, new directions are provided to researchers who work in the field of applications of nature-inspired optimization algorithms and coordination configuration of PSS and FACTS regulators.

The growing requirement to the clean and renewable energy has led to the rapid development of wind power systems all over the world. With increasing use of wind power in power systems, impact of the wind generators on subsynchronous resonance (SSR) is going more important. The SSR is a well-known phenomenon in a series compensated power systems which can be mitigated with series or parallel flexible ac transmission systems (FACTS) devices. In this paper, wind turbines and steam turbines have been used as a hybrid energy production system. For damping the SSR, thyristor controlled series capacitor (TCSC) as a series FACT devise and unified power flow controller (UPFC) as a series-parallel FACT device have been used. In order to have an optimal control on pitch angle in high speed of wind, a novel method using imperialist competitive algorithm (ICA) has been used. Furthermore, supplementary Controllers for UPFC and TCSC have been design and adaptive neuro fuzzy inference system (ANFIS) and fuzzy logic damping Controllers (FLDC) are added to these FACTS devises to mitigate the SSR. Finally, the results of two FACTS devises have been compared. Furthermore, the results obtained from imperialist competitive algorithm (ICA) are compared with PID controller optimized by Particle Swarm Optimization (PSO) algorithm.

After a disturbance occurrence, fast damping of power oscillations is essential to reduce the risk of instability and thus increase the power transfer capacity of transmission systems. Recently, the Static Series Synchronous Compensator (SSSC) has justified its ability to improve power oscillation damping. Due to substantial interactions among the SSSC damping control loops and the power system variables, the use of conventional Single-Input Single-Output (SISO) control approaches results in a poor damping performance. In this paper, these interactions are taken into consideration, and a power system equipped with an SSSC is modeled as a multivariable system. The impact of the SSSC’s dc voltage dynamic is also considered in the modeling. The power system equipped with an SSSC is multivariable with effective interactions among its variables. Traditional SISO control design techniques do not take into consideration these interactions and therefore cannot provide adequate damping over a wide range of operating conditions. Based on this developed multivariable modeling, a multivariable controller is proposed to improve power oscillation damping while keeping the dc-link voltage regulated. Simulation results verify the validity of the proposed modeling and control and show that the proposed approach can successfully damp out power system oscillations. Further simulation results show that the proposed controller provides a superior performance and a better robustness when compared to conventional SISO Controllers.

This paper deals with a modern approach of controlling the power flow in AC transmission lines. The control and distribution of power flow in two parallel transmission lines can be implemented by applying one of the flexible AC transmission system (FACTS), which is static compensator (STATCOM) device. The STATCOM device is installed on one line of the two parallel transmission lines to design the Controllers for such a system using Electromagnetic Transients Program (EMTP). The closed-loop STATCOM system as a terminal line voltage regulator is designed with two types of Controllers, PI with gain scheduling and fuzzy logic. The dynamic performance of the two Controllers is tested and compared. It is found that, the fuzzy logic controller forces the system to settle to the steady state value faster than the PI controller with gain scheduling. The fuzzy logic controller is robust; it has a fast response during disturbance and parameters variation. Whereas, the PI controller with gain scheduling has a higher overshoot percentage during transient behavior. Tuning the PI controller with gain scheduling is time consuming and difficult in EMTP, it has a limited range of changing the operating voltage condition due to the tuning difficulty. In the other hand, the fuzzy logic controller can be tuned much faster. Finally, It is claimed that the fuzzy logic controller is a better choice for the STATCOM system compared to the PI controller with gain scheduling.  

The growing demand increases the maximum utilization of transmission and distribution lines which causes overloading, high losses, instability, contingency, and congestion. To enhance the performance of AC transmission and distribution systems FACTS devices are used. These devices assist in solving different issues of transmission lines such as instability, congestion, power flow, and power losses. Advancement in developed technology leads to the development of special application-based FACTS Controllers. The main issues are concerned while placing the FACTS controller in the transmission and distribution lines to maximize the flow of power. Various methods like analytic method, arithmetic programming approaches, meta-heuristic optimization approaches, and hybrid approaches are being employed for the optimal location of FACTS Controllers. This paper presents a review of various types of FACTS Controllers available with both analytical and meta-heuristic optimization methods for the optimal placement of FACTS Controllers. This paper also presents a review of various applications of FACTS devices such as stability improvement, power quality, and congestion management which are the main issues in smart power systems. Today’s smart power systems comprise the smart grids with smart meters and ensure continuous high quality of power to the consumers.