The Research Of Limit Induced Bifurcation In Power System Static Voltage Stability

In recent years, a lot of voltage collapse accidents have occurred in many large power systems worldwide, which caused huge economic losses and great social disorder. Voltage stability has become a severe problem to power system. Bifurcation theory is a powerful tool to analyze structural stability of power system in theory and practice, so we can use it to research power system voltage stability. As power system voltage instability is monotonous mostly, so the research of static voltage stability has got widespread concern.In this paper, limit induced bifurcation in power system static voltage stability was researched on the basis of the research of nonlinear comprehensive dynamic equivalent method. The computational expression of comprehensive dynamic equivalent impedance was derived, which solved the online identification difficulty of comprehensive dynamic equivalent impedance. A necessary condition of maximum power of load node was proved. The condition is that load static equivalent impedance modulus is equal to comprehensive dynamic equivalent impedance modulus. On the basis of the computational expression of comprehensive dynamic equivalent impedance and the necessary condition of maximum power of load node, we analyzed weak nodes of systems and proposed a method to determine limit induced bifurcation combining impedance modulus margin index. According to this method, we can easily determine limit induced bifurcation as long as getting the impedance modulus margin when generator exceeds its reactive power limit. A necessary condition of limit induced bifurcation was proved. The condition is that power-angle is greater than critical power-angle. Moreover, the computational expression of critical power-angle was derived. Limit induced bifurcation was determined through comparing critical injected reactive power and injected reactive power when generator exceeded its reactive power limit. Limit induced bifurcation will occur when critical injected reactive power is less than injected reactive power when generator exceeds its reactive power limit. At the same time, the analytic calculation method of critical injected reactive power was proposed. The effectiveness of the proposed methods were demonstrated through the simulation of IEEE14-bus, IEEE30-bus and IEEE118-bus systems.