Sci.Int.(Lahore),25(3)451-456,2013 ISSN 1013-5316; CODEN: SINTE 8 451 POWER OSCILLATION DAMPING USING LEAD-LAG CONTROLLED SVC Karo Naqshi 2 , Mohyeddin Rahmani 1 , Behrooz Vahidi 1 , Seyed Hossein Hosseinian 1 1-Department of Electrical Engineering, Amirkabir University of Technology Tehran 1591634311, Iran 2- Deptartment of Electrical Engineering, University of Science and Technology, Tehran, Iran ABSTRACT: This paper proposes a new method to small signal stability improvement using controlled static VAR compensator (SVC). The linearized Phillips–Heffron model of a power system installed with a Static Var Compensator (SVC) is presented in order to increase the stability of the system parameters. Configuration of SVC in the power systems is widely adopted and effective to improve the power quality. In order to enhance the dynamic stability of power systems, this paper introduces the combination of static VAR compensator and lead-lag controller to compensate the reactive power. Feeding back the control signals, helps the controller to decrease the frequency oscillations of rotor, which are not negligible in the absence of lead-lag controller. The generator speed fluctuation (Δω) is the signal, which the combination of controller and SVC use to create the desired damping. As the result, creating the better damping for SVC, leads to better dynamic performance of system parameters, as well as reducing the steady-state errors. Also the settling times are reduced. The simulations are carried out for Single-Machine Infinite-Bus power system at two modes of operating. Key Words: Static VAR compensator (SVC), Lead-Lag damping controller, Small signal stability, Phillips- Heffron model 1. INTRODUCTION With great developments of modern power electronic devices, new application possibilities in several fields was made, like electrical power systems (EPS) and motor drives for electrical vehicles. The development of Flexible AC Transmission Systems (FACTS) devices is improving fast with the introduction of modern control techniques and new and improved power semiconductor devices [1,2]. Reactive power compensation is an important issue in electrical power systems and shunt FACTS devices play an important role in controlling the reactive power flow to the power network. Because of the good and fast response of the FACTS devices, and also their good ability to accommodate themselves to the system, many efforts have been made to use these devices instead of traditional power system stabilizers (PSS). This fast response of the FACTS devices, also results in reducing the transients of the system parameters. To overmatch the small disturbances, the power system must have a good dynamic stability which also maintains the synchronism between the system parameters. These small disturbances are the result of any change in power system, so they are continuously forced to the system. Many factors affect the dynamic response of the system to small disturbances, such as point of operating, system characteristics and the type of generator excitation. One of the most employed FACTS in the power systems are Static VAR Compensators (SVCs), in recent years SVC has been adopted widely since dynamic reactive-power control gives significant advantages for power system operation. Moreover the voltage control as a main task, SVC may also be employed for additional tasks resulting in improvement of the transmission capability [3-5]. The addition of dynamic voltage support or active power flow modification equipment can postpone the need for new transmission equipment and may also eliminate or postpone the need for new facilities. SVCs and FACTS devices provide rapid response to voltage irregularities and offer the opportunity to significantly improve the system performance in a cost effective manner. An important prospect when using SVCs is damping of power oscillations. Damping of power system oscillations plays a vital role not only in improvement the transmission capability but also for stabilization of power system parameters after critical faults, especially in inappropriate coupled systems. To achieve this objective, it is necessary to improve the SVC control concept by introducing signals which reflect power system oscillations. The normally used SVC voltage control is not suitable to effectively damp these oscillations [6-8]. To increase the effectiveness of SVCs, the complementary auxiliary control signals are adopted to decrease the rotor electro-mechanical frequency oscillations. In this paper the lead-lag controller is proposed using the generator speed fluctuation (Δω), as a modulated signal to SVC. The operation of SVC is described briefly in part II. Section III includes the model of power system e.g. single-machine infinite-bus, synchronous generator and exciter, and lead-lag controlled SVC. The simulations are carried out for Single- Machine Infinite-Bus power system and results are in part IV. Conclusions and future works are presented in section V to verify the validity of the proposed method. 2. STATIC VAR COMPENSATOR (SVC) A Static VAR Compensator (SVC) is an electrical device for providing fast-acting reactive power on high-voltage electricity transmission networks. SVCs are part of the Flexible AC transmission system device family, regulating voltage and stabilizing the system. The term static refers to the fact that the SVCs have no moving parts (other than circuit breakers and disconnectors, which do not move under normal SVC operation). Prior to the invention of the SVC, power factor compensation was the preserve of large rotating machines such as synchronous condensers. A SVC