IEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING IEEJ Trans 2013; 8: 550–556 Published online in Wiley Online Library (wileyonlinelibrary.com). DOI:10.1002/tee.21895 Paper Damping of Low-Frequency Oscillations using an SVC-Based Supplementary Controller Hamed Hasanvand a , Non-member Bashir Bakhshideh Zad, Non-member Babak Mozafari, Non-member Behnam Feizifar, Non-member In this paper, the optimal tunning problem of parameters of a conventional lead–lag controller (LLC) and a fuzzy logic controller (FLC) based on the static Var compensator (SVC) is considered. The solution is obtained using an improved particle swarm optimization (IPSO) algorithm. The membership functions and scaling factors of the FLC and LLC parameters are optimized using the above-mentioned technique. The proposed controllers are settled down to an SVC that is installed at the middle of a transmission line connecting a single machine to an infinite bus system. Simulation results show the superiority of the optimized FLC compared to the optimized LLC and also when the SVC is without the supplementary controller under different disturbances and loading conditions. The simulations and analyses are implemented in MATLAB environment. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. Keywords: low-frequency oscillations, static Var compensator, lead–lag controller, fuzzy logic controller, improved particle swarm optimization algorithm Received 24 February 2012; Revised 27 August 2012 1. Introduction Power systems are often subjected to low-frequency oscilla- tions due to electrical disturbances [1]. Interconnection of large power systems by weak tie lines increases the possibility of low- frequency oscillations from 0.2 to 3 Hz in the network. When suit- able damping is not available, these oscillations may sustain and become larger, causing system breakdown [2]. Power system sta- bilizers (PSSs) are designed to provide sufficient damping against this kind of oscillations. However, in some certain circumstances, because of generator reactive power limitations and voltage regu- lation through the excitation system, PSS by itself cannot provide suitable damping requirements. In such cases, supporting the sys- tem by auxiliary voltage and reactive power control equipment will become necessary. With the advent of flexible AC transmis- sion systems (FACTS) technology, shunt FACTS devices play an important role in controlling the reactive power flow of power systems and hence improving the system voltage stability [3,4]. One of the most important members of these shunt devices is the static Var compensator (SVC). The primary application of the SVC is to maintain the voltage of the connection point within an acceptable range. In addition, SVC can improve transient stabil- ity by fast exchange of reactive power with the network. Besides reactive power control and voltage regulation as SVC’s pivotal functions, supplementary control blocks can be accommodated to modulate the SVC bus voltage in order to improve the damping of power system oscillations [5,6]. Various approaches have been proposed in the literature for designing a supplementary damping controller aiming at enhancing the power system stability. A com- mon approach is to design controllers using the linear feedback a Correspondence to: Hamed Hasanvand. E-mail: Hamed_hasanvandb@yahoo.com Department of Electrical Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran control theory. Recently, two types of linear damping controllers for an SVC were suggested to accommodate extreme operating conditions [1]. Also, a lead–lag damping controller for the SVC based on eigenvalue analysis has been reported [6]. Moreover, a supplementary proportional-integral-derivative (PID) controller whose parameters are determined by eigenvalue assignment has been developed [7]. Although such controllers are fairly simple and easy to design, they require a mathematical linear model of the system around a certain operating point. This often causes the designed linear controller to show satisfactory performance just for a small perturbation of power systems. As large disturbances move the system operating condition significantly, the performance of such linear controllers usually deteriorates. An outstanding feature of the fuzzy logic controller (FLC) is its effectiveness and robust- ness over a wide range of loading conditions and disturbances. Therefore, to tackle problems with a high degree of nonlinear- ity and uncertainty, FLC is considered as a suitable approach. In addition, the design procedure is independent of the mathematical model of the power system. This provides an opportunity to handle the nonlinearity of the power system by designing the FLC [8,9]. In recent years, much effort has been directed toward the applica- tion of FLC as an SVC controller in order to improve power system stability [10,11]. It is worth mentioning that, to obtain a better performance by an FLC, tuning the parameters associated with membership functions in an optimal way is crucial. Convention- ally, trial-and-error methods are used to adjust these parameters. Because of the fact that the tuning of membership functions and scaling factors using these methods is difficult, an improved par- ticle swarm optimization (IPSO) algorithm is introduced [12]. In this paper, the aim is to design a proper supplementary damping controller for an SVC in order to damp out low-frequency oscilla- tions. Therefore, IPSO is implemented to determine the optimized lead–lag controller (OLLC) parameters. Also, the scaling factors and membership functions of the FLC are tuned by the IPSO. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.