Methods for small signal analysis of very large power systems

The size of the interconnected power system in North America has grown to such an extent that, if dc links are included, all utilities in the U.S. and Canada form constituent parts. Recent economic and environmental pressures have caused the system to become more highly stressed than in the past and this has caused low frequency, highly oscillatory modes to have been observed on the system on a number of occasions. These low frequency modes have been found to be caused by groups of relatively closely coupled machines, oscillating across weak transmission links. For such modes, the normally used reduction techniques may not be sufficiently accurate and, consequently there is a need to study the problem using very large power sytem models. In this paper, a general review of the small signal analysis of power systems is given. The special requirements for the analysis of very large systems are stressed and a number of methods, recently developed for such analysis, are discussed in detail. Those problem areas still to be resolved are identified and suggestions are made for the future development of power system small signal analysis programs.