Heuristic method to identify the smallest stability margin due to bifurcations considering different load patterns

Abstract

Power systems currently operate close to their stability limits due to economic and environmental restrictions. Under these operating conditions, three types of bifurcations may be close: the Saddle-Node (SNB), Hofp (HB), and Limit-Induced Bifurcations (LIB). These bifurcations are characterized by qualitative and quantitative changes in the system happen as one of its parameters (usually the load level) varies and creates an unstable behavior in the system. In stability studies, the stability margin (SM) is defined as the distance between the current operating point and the one in which one of these bifurcations occur. In the literature, it can be seen that the majority of the methods to identify this margin assumes that the load grows in a specific direction, typically taking into account the inertia constants of the generators. However, this estimate of the margin may not be precise since the variations of the load patterns in the system may not follow this assumed direction of growth. This problems is particularly critical in deregulated system where the power generation and the load levels are influenced by economic factors. Therefore, the load growth must be treated as a system uncertainty. Little attention has been given to the problem of identification of a load pattern or growth direction that leads to the least conservative stability margin. Having this in mind, the objective of this undergraduate research project consists in obtaining the load growth direction or load pattern that results in the smallest stability margin of the system. To this end, an optimization problem will be formulated and solved using different methods and, later on, a comparison among them will be made. (AU)