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