A comparison of dynamic security indices based on direct methods

Abstract

This paper presents a comparison of direct methods for transient stability assessment. The emphasis is on stability criteria based on Lyapunov's direct method. The comparison is made by studying the similarities and differences in the regions of attraction which the direct methods define. The region of attraction is characterized in terms of a performance index (PI) and a threshold value (TH). This paper reformulates the various Lyapunov energy functions and stability criteria for the direct methods proposed in the literature in a unified mathematical notation. Specifically, each energy function is reformulated in terms of a general form of the PI and each type of stability criterion is restated in terms of a threshold value, TH. Comparison tables are presented to identify the similarities and differences in the PI parameters, threshold values and dynamic models. These tables are used to show the correctness of several relationships among the direct methods mentioned in the literature and to derive new relationships for the similarities and differences between the direct methods.