Influence Of The Generator Damping And Parameter Fluctuation To Power System Stability

Modern power systems are featured with extra high voltage level, long-distance and heavy power transmission, and inter-area connection. They are now operated approaching to their stability limit due to the economical and environmental constraints. More and more attentions are paid on power system stability and security studies nowadays. Among all power stability, small signal stability is regarded as the basic requirement for power system normal operation. Eigen-based method is the basic tool for the traditional small signal stability analysis. Recently, bifurcation theory is applied to power system small signal stability analysis. Based on this method, system global bifurcation and stability characteristics can be easily obtained. In this thesis, eigen-method and bifurcation theory are both used to analyze the influence of generator damping model and parameter fluctuation to power system small signal stability. Main work of this thesis is as following:Firstly, two generator damping models used in power system small signal stability study are compared. Generator damping is a typical nonlinear function of generator speed. It is also influenced with the generator operating conditions. However, in traditional stability studies, generator damping is usually treated as a linear function of generator speed for simplification. In this thesis, linear damping model and a so-called Liwschitz nonlinear damping model are compared in power system small signal stability analysis. It can be found that the system bifurcation diagrams are different when the damping models are different. E.g., although there both exist chaos in the power systems with two damping models, the chaotic areas, the system bifurcation diagrams and the bifurcation types are different.Secondly, influence of the parameter fluctuations to power system stability is discussed. We calculate the system dynamic with time-domain simulation when system is under an equilibrium point and some parameter (such as exciter gain KA) changes. The maximum parameter fluctuating ranges, i.e. the parameter disturbance stability region, under different load levels are also determined. It can be found that boundary of the stability region is not convex. Eigen-based method and bifurcation method are used to analyze the topological characteristic of the region's boundary.Works of the thesis are helpful to select appropriate generator damping model in power system stability analysis and to determine the reasonable fluctuating range of the key system parameters. More works should be done in the future.