Using the coherency function to detect large-scale dynamic system modal observability

Shows that the standard coherency function provides rich information about a system's observability characteristics. Specifically, linearizable large-scale systems with oscillatory dynamics are considered. Also, it is assumed that the system is excited by several random inputs. Cross-correlation of system outputs using the coherency function is shown to be a strong indicator of a particular system mode's (i.e., oscillatory pole's) participation or observability. Because the coherency can be estimated using standard FFT analysis of actual measured signals, the results enable useful information for advanced large-scale system monitoring and operation. This is demonstrated using a two-area four-generator interconnected power system example.