Study on models and methods for identifying of voltage stability limit more precisely

With the increasing concerns for more precise description of voltage stability limit in modern power systems, we investigated some models and methods required in this work. First, bifurcation method and so-called two-step method were both applied to a two-bus system, bringing up the first special characteristic of induction motor model: A SNB induced by stalling of motors always occurs well before Fold bifurcation point and SNB does not coincide with Fold in general sense. We proved this conclusion using analytic forms of the simple system. Then, the relationships between Continuation Power Flow (CPF), bifurcation and two-step method were revealed. Further application of these methods on a 9-bus system showed the second special characteristics of induction motor model: It is not all SNB with motors would lead to voltage instability and the system behavior at these SNBs will also depend on operating condition. The property of SNB could be verified either by bifurcation diagram or via time domain simulation with two-step method. Finally, a test on 1000-bus system confirms the complexity brought out by induction motor model and effectiveness of two-step method in computing voltage stability limit in a higher degree of precision.