Abstract
Recently, voltage instability has been becoming one of major problems of power systems, and therefore, a lot of researchers have been studying this problem. A recent major topic arising as the results of these studies is associated with the mechanism leading to voltage collapse, especially the contribution of load dynamics to this phenomena. In fact, different assumptions as to load representations, that is static or dynamic, have given different analysis results in many previous studies. Further, the theoretical interpretation about the difference has not yet been given completely up to now.
This paper provides a resolution of the above problems by extending the authors' previous study(9), in which possible voltage instability patterns have been classified into four types. In the first half of this paper, the relationships among the classified instabilities are theoretically derived using a general expression of load dynamics. The theoretical meaning of general analysis results under static and dynamic load representations is also examined here. Then, taking Nagao's simulation method as an example(10), the effectiveness of this method is studied from the view point of its inherent characteristics as well as analysis errors caused by its assumption of static loads. In the latter half, these theoretical results are verified through numerical simulations in IEEE 14 test system, with taking into account dynamic characteristics of generators, controllers, tap changers, induction motor loads, etc.
