Estimation of electro-mechanical mode parameters using frequency measurements

Oscillation frequency and damping of electro-mechanical modes in a power system have traditionally been determined from events caused by large disturbances such as line switchings or generator tripping. Recent papers have shown the possibility to extract this information during normal operation from measurements of power through, or angle difference across, a transmission line. In this paper these methods are applied to frequency measurements from a 230 V wall-outlet. If accurate frequency and phase estimates can be obtained, this can be used for load control to damp electro-mechanical oscillations. Doing this in the distribution system is easier than in the transmission system. Using frequency for this has the advantage that this signal is available everywhere. It would thus be convenient if the estimation of modes and damping could be done in the distribution system. The results show that it is much harder to detect electro-mechanical mode information from frequency than from angle difference or power. However, it is possible to find the frequency of two electromechanical modes whereas the damping has too large an uncertainty. Fundamental problems when using frequency for mode estimation are further discussed.