The event analysis engine, shown on the right side of the flow chart, carries out an expert system–based Prony-type ringdown analysis of system responses following disturbances or oscillations in the system. The objective for this engine is fast detection of poorly damped oscillations from sudden events in a power system, so that they can be analyzed and mitigating control actions can be initiated before the oscillations lead to potential equipment damage and outages. Event analysis engine uses four algorithms, namely, Prony, Matrix Pencil (MP), Eigenvalue Realization Algorithm (ERA) and Hankel Total Least Square (HTLS) together with multiple crosschecks to ensure the accuracy and reliability of ringdown analysis results.

The complementary damping monitor engine, shown on the left side of the flow chart, estimates the damping, frequency, and mode shape of poorly damped oscillatory modes from ambient PMU measurements. Unlike the event monitor engine, which only works when the system is subject to disturbances, the damping monitor engine is applicable all the time. By using natural power system responses to routine random fluctuations from load variations and generation changes, the damping monitor engine continuously tracks damping levels and mode shapes of poorly damped oscillatory modes. Damping monitor engine uses two algorithms, namely, Fast Frequency Domain Decomposition (FFDD) and Fast Stochastic Subspace Identification (FSSI) to estimate the dominant modes, their frequencies, damping and energy levels from wide area synchrophasor measurements continuously.