www.sciencerecord.com Journal Title: xxxxxxxxxxxxxxxxxxx Vol. x, No. x; Month 2011 1 ISSN xxxx-xxxx E-ISSN xxxx-xxxx Fuzzy Controller Performance for Static Synchronous Series Compensator (SSSC) to Increase Power System Stability Mostafa Bayati MSc Mechatronic Student, Department of Computer and Electrical Engineering, Semnan University, Semnan, Iran E-mail: M_bayati@sun.semnan.ac.ir Mohammad Karimi Young Researchers Club, Parsabad Moghan Branch, Islamic Azad University, Parsabad Moghan, Iran E-mail: m.karimi@iaupmogan.ac.ir Mehdi Pazhoohesh MSc Energy and Sustainability with Electrical Power Engineering, University of Southampton, United Kingdom, Student member of IEEE E-mail: mp3e11@soton.ac.uk Abstract So far several controllers such as conventional PI, PID controllers have been utilized in FACTS controllers control system for active and reactive power control in HVAC transmission lines, and hence oscillations occurred in power system are damped. In this paper, Fuzzy controller is used in the control system of one of the FACTS member i.e. static synchronous series compensator (SSSC) to increase its response appropriately, especially in power system critical conditions. In this paper it is tried to obtain the goals of damping transient oscillations and reaching steady state quickly as well as pursuing the reference values properly. Simulation results showed that. Simulations have been performed in MATLAB/SIMULINK environment. To show the effectiveness of the proposed controller, its results have been compared with the two other controllers in Peak and Fall values also Settling time for which Fuzzy controller could lead to better results in all parameters. Keywords: FACTS, Fuzzy controller, Static synchronous series compensator, Transient oscillations, Power system stability 1. Introduction Increasing demand for electrical energy causes that transmission lines to be used in their maximum operation limits. Also, due to the interconnection of large power systems to each other, oscillations are occurred in power systems that their amplitude may be increased if they are not damped properly and this consequently will result in power system instability. In the past three decades, power system stabilizers (PSSs) have been extensively utilized to increase the system damping for low frequency oscillations. The power utilities worldwide are currently implementing PSSs as effective excitation controllers to enhance power system stability [1–5]. However, there have been problems experienced with PSSs over the years of operation. Some of these were due to the limited capability of PSS in locally damping only and not inter-area modes of oscillations. In addition, PSSs can cause great changes in voltage profile under severe disturbances and they may even result in leading power factor operation and losing system stability [6]. The Electric Power Research Institute (EPRI) formulated the vision of the Flexible AC Transmission Systems (FACTS) in which various power-electronics based controllers regulate power flow and transmission voltage and mitigate dynamic disturbances. Generally, the main objectives of FACTS are to increase the useable transmission capacity of lines and control power flow over transmission lines.