Method For Voltage Stability Assessment Research Articles

Power System Voltage Stability Assessment Using Enhanced Power Flow Models

This paper presents an enhanced method for power system voltage stability assessment. Key features of this method are the inclusion of the characteristics of key dynamic devices and an efficient method to solve the associated algebraic and differential equation sets in steady-state conditions. It offers an accurate representation of equipment operating characteristics for voltage stability margin calculation. The importance of the proposed modeling approach is demonstrated with simulation results.

Complete controllability of an N-bus dynamic power system model

As the computational and analytical methods for voltage stability assessment become more mature, voltage control becomes a primary issue. Power systems are large, nonlinear, and dynamic. During the last three decades, the application of differential geometry in the area of nonlinear control has produced significant results for the controllability analysis. This paper is concerned with the controllability problem of power systems using the differential geometric methods. The modeled control devices include the mechanical power input to generators, VAr compensation devices, and tap settings of the on-load tap changers. Conceptually, the main result of this research is the characterization and construction of a complete controllability region, within which a power system can be steered from one state to another by use of piecewise constant controls. The results are obtained for two cases: (1) unbounded piecewise constant controls and (2) bounded piecewise constant controls. A complete controllability region identifies the limitations of the available controls of a power system. The proposed method is believed to be significant since it is a new and systematic approach to the analysis of power system controllability using a nonlinear control system model.

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 is based on the standard load flow equations. For small-disturbance analysis, 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 point 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 implicit assumptions on the steadystate behaviour of dynamic components (generator control systems, loads). These assumptions are not satisfied by the usual dynamic models, and this discrepancy leads to different results in the voltage stability assessment using static and dynamic methods. In the framework of bifurcation theory, this paper discusses the relationships between static and small-disturbance dynamic approaches to find the voltage stability critical condition, with emphasis on system component modelling. A set of hypotheses on generator control systems and load models is given for a multimachine system, according to which the same critical conditions are obtained both from the load flow 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 may justify the use of simple and fast static methods for voltage stability assessment and shows that the smalldisturbance voltage stability limit depends only on the steady-state characteristics of the dynamic components of the system.