On-line modal analysis based on synchronized measurement technology

This paper proposes a new approach for modal analysis of a large power system that is based on the on-line system identification by using the synchronously measured responses of remote machines. Since the power system is identified as a linear dynamic system, the eigenanalysis can provide the damping constants, modal frequencies and mode shapes of the weakly damped electromechanical modes that appear in the measurer: responses at an operating point. In the paper, it is also discussed how to select a small number of the machines suitable for detecting slow oscillatory modes and estimating the eigenvalues of slow modes. Such machines can be found out by utilizing the slow coherency observed in the global motion between groups of machines. The verification of the new modal analysis and the coherency based machine selection is done by simulation studies of a 3-machine and 9-bus system, and a 25-machine and 66-bus system.