Research On Transient Stability Limits Using Trajectory Sensitivities

Research on the stability limit analysis is always one of the critical issues for power system. In literature, two approaches in stability analysis are presented: one is through the repetitive time domain simulations and the other derived from the characteristic of transient energy margin. The former has the advantage of details in model and high accuracy in results while the latter is efficient to the on-line analysis. In this paper, a new research combined with the advantages of the two techniques is proposed to compute stability limits including critical clearing time (CCT) and generation limits of generators using trajectory sensitivity.Trajectory sensitivities are traditionally classified as α sensitivity (to system parameters) and β sensitivity (to initial state). New formulations, different from β sensitivity, of post-fault trajectory sensitivity to fault clearing time (t_cl) are first presented through the use of mathematical deduction. Based on the characteristics of minimum corrected kinetic energy (CKE) and normalized kinetic energy (NKE) versus t_cl curves, an iterative method directed by the minimum kinetic energy sensitivity (CKE or NKE) to t_cl is proposed to estimate CCT. With the mapping technique from the trajectory sensitivity to kinetic energy sensitivity, the problem that time when minimum kinetic energy of post-fault trajectory arrives differs from distinct t_cl is resolved in this thesis. With corporation of the simulation of α sensitivity, similar approach can be utilized to estimate the critical outputs of generators.The new approach to estimate transient stability limits is independent of system model and its high efficiency comes from no more than two iterations. Case studies on New England test system validate its effectiveness and efficiency thoroughly.