786 IEEE TRANSACTIONS ON POWER SYSTEMS, VOL. 18, NO. 2, MAY 2003 Comparison of PSS, SVC, and STATCOM Controllers for Damping Power System Oscillations Nadarajah Mithulananthan, Member, IEEE, Claudio A. Canizares, Senior Member, IEEE, John Reeve, Fellow, IEEE, and Graham J. Rogers, Fellow, IEEE Abstract—This paper discusses and compares different control techniques for damping undesirable interarea oscillation in power systems by means of power system stabilizers (PSS), static var compensators (SVCs), and shunt static synchronous compensators (STATCOMs). The oscillation problem is analyzed from the point of view of Hopf bifurcations, an “extended” eigenanalysis to study different controllers, their locations, and the use of various control signals for the effective damping of these oscillations. The compar- isons are based on the results obtained for the IEEE 50-machine, 145-bus test system, which is a benchmark for stability analysis. Index Terms—Hopf bifurcations, power system oscillations, PSS, STATCOM, SVC. I. INTRODUCTION E LECTROMECHANICAL oscillations have been ob- served in many power systems worldwide [1]–[4]. The oscillations may be local to a single generator or generator plant (local oscillations), or they may involve a number of generators widely separated geographically (interarea oscillations). Local oscillations often occur when a fast exciter is used on the generator, and to stabilize these oscillations, power system stabilizers (PSS) were developed. Interarea oscillations may appear as the systems loading is increased across the weak transmission links in the system which characterize these oscillations [4]. If not controlled, these oscillations may lead to total or partial power interruption [2], [5]. Electromechanical oscillations are generally studied by modal analysis of a linearized system model [2], [6]. However, given the characteristics of this problem, alternative analysis techniques can be developed by using bifurcation theory to effectively identify and control the state variables associated with the oscillatory problem [7]–[10]. Among various types of bifurcations, saddle-node, limit-induced, and Hopf bifurcations have been identified as pertinent to instability in power systems [11]. In saddle-node bifurcations, a singularity of a system Jacobian and/or state matrix results in the disappearance of steady state solutions, whereas, in the case of certain limit-in- duced bifurcations, the lack of steady state solutions may be Manuscript received October 2001; revised April 2002. This work was sup- ported in part by NSERC and in part by the E&CE Department at the University of Waterloo. N. Mithulananthan is with the Asian Institute of Technology, Bangkok, Thai- land (e-mail: mithulan@ait.ac.th). C. A. Cañizares and J. Reeve are with the Department of Electrical and Com- puter Engineering, University of Waterloo, Waterloo, ON, N2L-3G1, Canada (e-mail: ccanizar@engmail.uwaterloo.ca). G. J. Rogers is with Cherry Tree Scientific Software, Colborne, ON, K0K-1S0, Canada. Digital Object Identifier 10.1109/TPWRS.2003.811181 associated with system controls reaching limits (e.g., generator reactive power limits); these bifurcations typically induce voltage collapse. On the other hand, Hopf bifurcations describe the onset of an oscillatory problem associated with stable or unstable limit cycles in non linear systems (e.g., interconnected power system). The availability of flexible ac transmission system (FACTS) controllers [12], such as static var compensators (SVCs), thyristor control series compensators (TCSC), static syn- chronous compensators (STATCOMs), and unified power flow controller (UPFCs), has led their use to damp interarea oscillations [13]–[15]. Hence, this paper first discusses the use of bifurcation theory for the study of electromechanical oscillation problems, and then compares the application of PSS, SVC, and STATCOM controllers, proposing a new controller placement technique and a methodology to choose the best additional control signals to damp the oscillations. The paper is organized as follows: Section II introduces power system modeling and analysis concepts used throughout this paper; thus, the basic theory behind Hopf bifurcations and the modeling and controls of the PSS, SVC, and STATCOM controllers used are briefly discussed. Oscillation control using SVC and STATCOM controllers, including a new placement technique, is discussed in Section III. In Section IV, simulation results for the IEEE 50-machine test system are presented and discussed, together with a brief description of the analytical tools used. Finally, the major contributions of this paper are summarized in Section V. II. BASIC BACKGROUND A. Power System Modeling In general, power systems are modeled by a set of differential and algebraic equations (DAE), that is (1) where is a vector of state variables associated with the dynamic states of generators, loads, and other system con- trollers; is a vector of algebraic variables associated with steady-state variables resulting from neglecting fast dy- namics (e.g., most load voltage phasor magnitudes and angles); is a set of uncontrollable parameters, such as variations in active and reactive power of loads; and is a set of con- trollable parameters such as tap and AVR settings, or controller reference voltages. 0885-8950/03$17.00 © 2003 IEEE