Weighted update method for spectral mode shape estimation from PMU measurements

A method of tracking a power system´s electromechanical mode shape and coherence over time is presented. It uses an algorithm of weighted-updates to efficiently compute an existing spectral estimation algorithm. The advantage of this over other mode shape estimators is that it overcomes the assumption that the system being estimated is stationary. The relationship between spectral densities and mode shape and coherence is reviewed. The method is applied to both a simulated system and measured data from the western North American power system. It is shown to accurately track the mode shape and coherence over time in the presence of a major system configuration change.