A DYNAMIC INTERPRETATION OF THE LOAD-FLOW JACOBIAN SINGULARITY FOR VOLTAGE STABILITY ANALYSIS

In voltage stability analysis, both static and dynamic approaches are used to evaluate the system critical conditions. The static approach i s based on the standard load-flow equations. For small-disturbance ana lysis, the dynamic approach is based on the eigenvalue computation of the linearized system, while for large-disturbance analysis a complete time-domain simulation is required. However, both the equilibrium poi nt around which linearization is performed and the initial conditions for the simulation are computed by a procedure which uses the standard load-flow equations. The standard load-flow equations make some impli cit assumptions on the steady-state behaviour of dynamic components (g enerator control systems, loads). These assumptions are not satisfied by the usual dynamic models, and this discrepancy leads to different r esults in the voltage stability assessment using static and dynamic me thods. In the framework of bifurcation theory, this paper discusses th e relationships between static and small-disturbance dynamic approache s to find the voltage stability, critical condition, with emphasis on system component modelling. A set of hypotheses on generator control s ystems and load models is given for a multimachine system, according t o which the same critical conditions are obtained both from the load-f low equations and from the full eigenvalue analysis. These hypotheses are less restrictive than those previously proposed in the literature and make it possible to obtain equivalence between the singularity of the load-flow Jacobian and a null eigenvalue of the linearized dynamic system. Following a dynamic argumentation based on small-disturbance analysis, this result maq!justify the use of simple and fast static me thods for voltage stability assessment and shows that the small-distur bance voltage stability limit depends only on the steady-state charact eristics of the dynamic components of the system. (C) 1996 Elsevier Sc ience Ltd.