Introduction

The objective of the application of stabilizers in multi-machine power systems is to stabilize the system by providing adequate damping for the critical rotor modes of oscillation. These modes typically involve several power stations and their machines. In the case of inter-area modes many power stations, geographically widely separated, may participate in both the local and inter-area modes. It is therefore necessary that the stabilizer which, when fitted to a generator, contributes with stabilizers on other machines to the damping of the relevant modes. Furthermore, because operating conditions on the system continuously change, the performance of a fixed-parameter stabilizer should be robust to any such changes.

By employing the P-Vr method in the tuning of the PSS, as demonstrated in Chapter 5, the inherent magnitude and phase characteristics of the generator and power system are being utilized; for practical purposes these characteristics consistently lie in a relatively narrow band. Not only can the method account for variations over a wide range of loading conditions on the system, line outages, etc., but the resulting PSS is most effective and beneficial at the higher generator real power outputs as revealed in Table 5.6, and discussed in the associated text.

Prior to considering the application of the P-Vr method to the tuning of PSSs in multi-machine power systems, the use and significance of two valuable tools in the small-signal analysis of the dynamic performance of such systems are discussed. These tools concern the so-called “Mode Shape” and “Participation Factor” analyses of the system for a selected operating condition. Such analyses reveal the nature and significance of the various modes (both rotor or other modes), the involvement - and extent of involvement - of generators in the modes, and other insights such as the nature of the dynamic behaviour of other devices in the system (e.g. FACTS devices and their controls).

The application of other PSS tuning methods, namely the GEP Method and the Method of Residues, is discussed in Chapter 6. While these approaches can be adapted to the multi-machine system, for the reasons explained in the latter chapter the P-Vr method is considered to possess some significant advantages.