ELSEVIER Electrical Power & Energy Systems, Vol. 18, No. 5, pp. 307 313, 1996 Copyright © 1996 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0142-0615(95)00072-0 0142-0615/96/$15.00 + 0.00 Application of the Phillips-Heffron model in the analysis of the damping torque contribution to power systems by SVC damping control H F Wang and F J Swift Department of Electrical and Electronic Engineering, Manchester Metropolitan University, Manchester, UK In this paper, an extended Phillips-Heffron model of a power system installed with a static VAr compensator ( SVC) is established and applied to analyse the damping torque contribution of SVC damping control to the power system. Some basic iss'aes, such as the capability of the SVC damping control to supply positive damping to the power system, the best location of the SVC damping control, its control strategy and its robustness to the changes of the operating conditions of the power system, are investigated. Previous findings from numerical calcula- tions and simulations of the effects of SVC damping control are confirmed by the analytical results in the paper. To supplement the analysis, the results of the calculations and simulations o fan example power system are also presented. Copyright © 1996 Elsevier Science Ltd. Keywords." static VAr compensator, Phillips-Heffron model, damping torque, power system oscillation stability I. Introduction With the rapid development of power electronic tech- niques, it has become both practical and economic to apply thyristor-controlled reactive power compensators, or static VAr compensators to the improvement in the performance of power systems for more efficient opera- tion. One of the major applications of the SVC installa- tion in a power system is to enhance the system transient stability by the SVC dynamic voltage control. However, it has been found that SVC voltage control does little to help the oscillation stability of the power system. In order to improve power system damping and increase system oscillation stability, it has been suggested that an additional stabilizing signal be superimposed on Received 9 March 1995; accepted 17 August 1995 the SVC voltage control. This forms an extra damping control loop and provides positive damping to the power system. For such an arrangement of the SVC damping control it has been found that, with proper design, it can work very efficiently. SVC damping control provides an alternative means to improve system damping to the usually used power system stabilizer (PSS). Recently, many researchers have devoted effort to this subject 1-5, especially in Reference 6, where graphical explanations based on the use of well-known equal area criteria are presented concerning some basic issues in SVC damping control. The explanation of these issues, such as why the system damping can be improved by SVC damping control, the best location of the SVC installation for the most efficient damping control and so on, provides better understanding about the effect of the SVC damping control on improving power system oscillation stability. In this paper, an extended Phillips-Heffron model of a power system with an SVC is established. By use of this P-H model, the damping torque contribution of the SVC damping control to the power system is analysed, so as to present an analytical explanation of the basic issues concerning SVC damping control, which are: (1) the capability of the SVC to supply positive damping to the power system; (2) the best location of the SVC damping control; (3) its control strategy; and (4) its robustness to the changes of the operating con- ditions of the power system. The analysis, based on the extended P-H model, not only gives results which are in accordance with those obtained in References 1-6 by numerical calculation, simple analysis and graphical explanation, but also shows that SVC damping control can become more effective with increases in the transmission line impedance. The work in this paper provides theoretical confirmation of 307