Introduction

Various techniques have been reported in the literature for the coordination of PSSs in multi- machine power systems [1], [2], [3], [4]. Some of these techniques have used linear programming solutions for coordinating PSS gains [5], [6]. However, little attention has been given to the simultaneous coordination of PSSs and FDSs [7], [8], [9] [10]; this aspect is the subject of this chapter. It must be emphasized that in the current context the term ‘coordination’ is used to mean coordinating the gains of stabilizers installed on generators and FACTS devices, say, in an area of interest for the purpose of improving the damping of rotor modes. This is as opposed to coordination in the context of coordinating controllers, e.g. AVR-PSS coordination, within a single generating unit [11]. In the following text the damping gains of PSSs and the gains of FDSs are collectively referred to as stabilizer gains.

It has been emphasized that the predominately left shift of the modes with increasing stabilizer gain is the objective of the design procedures outlined in Chapters 5 and 10 for PSSs and Chapter 11 for FDSs. In essence, because the stabilizer transfer functions are of the form kG(s), where is k a real gain and the transfer function G(s) provides the phase compensation, then ideally, (i) G(s) ensures the left shift of all modes over the selected range of modal frequencies, and (ii) the gain k determines the extent of the left-shift of the mode. This basic approach to the tuning of stabilizers provides the following rationale for the methods of heuristic and automated coordination.

1. • In both the heuristic and automated coordination procedures the stabilizer gain and the phase compensation are the two important components which are essentially decoupled for practical purposes. Therefore, in the coordination procedures that follow, the stabilizer gains are the adjustable quantities and the parameters of the compensation transfer functions remain G(s) unchanged.

2. • For the process of stabilizers coordination the PSSs and FDSs should be robust over an encompassing range of operating conditions, normal and outage (see Section 1.2 item 3 and Section 11.8.2, respectively).

3. • Ideally, the incremental left-shifts of the rotor modes should be more-or-less linearly related to increments in stabilizer gain for small changes about the nominal values.