A novel method for online voltage stability assessment based on PMU measurements and Thevenin equivalent

Abstract

From the power systems security point of view, determining the voltage stability margin is essential for the operation of systems. An inaccurate determination of the maximum loading factor or voltage collapse point in a power system may cause voltage instability and blackout of the system. So, applying a proper method with high accuracy and high speed is vital in analysing voltage stability in power systems. This article presents a novel method based on Thevenin equivalent of power systems to accurately determine load-ability margin using phasor measurement units (PMUs) data. The proposed method is based on the fact that at the voltage collapse point, the characteristic curves of ‘the reactive power at the receiving end’ and ‘the reactive power of the load’ in the weakest bus are tangential to each other. Furthermore, online application of the proposed method requires accurate estimation of the ‘ZIP load model’ and ‘Thevenin equivalent’ of the system. The proposed method is designed to determine the load-ability margin, ZIP load model and Thevenin equivalent of the power system, simultaneously. This characteristic of the method makes it possible to be applied for online voltage stability assessments. To demonstrate the effectiveness of the proposed method, the simulation results for IEEE 14-bus, 39-bus New England and IEEE 300-bus are presented and analysed.