Small-signal stability modelling and analysis of power systems with electronically controlled compensation

Flexible AC Transmission Systems (FACTS) equipment is currently being incorporated into the power system for controlling key networks parameters aiming at improving the power system steady-state and dynamic performances. The vast array of power system analysis tools used by planners and system operators, on a daily basis, for the successful running of the network are to be upgraded to include comprehensive modelling for FACTS plant components. Commensurate with this global objective, this research work is aimed at developing comprehensive power system models of FACTS devices suitable for small-signal stability studies. The FACTS components covered in this research are the Static Var Compensator (SVC) and the Thyristor-Controlled Series Capacitor (TCSC). More specifically, the modelling of these devices combined with advanced modelling of synchronous generators has positioned the current work in the area of small-signal stability modelling and analysis of power systems with electronically controlled compensation. The work has been developed within the framework of the block-diagram methodology because it yields physical insight and offers the opportunity to gain fundamental knowledge of the dynamic interactions taking place between synchronous generators and FACTS plant components. The key issues of synchronous generator modelling, from the viewpoint of small-signal stability analysis, are addressed in this thesis. In particular, the impact of synchronous generator modelling order, with emphasis on system damping, is discussed in depth. Various representations of salient-pole synchronous generators are used to enable a variety of models suitable for small-signal stability studies. The models range from synchronous generators with no danger windings, to cases when one damper winding is included in each of the rotor axes, i.e. d and q-axis. The drive behind the study is to settle the issue of what is a suitable number of machine damper windings to be used in small-signal stability analysis that adequately represents the system model with a good level of reliability while keeping engineering complexity manageable.