Low-Frequency Inter-Area Mode Detection in Power System using Continuous Wavelet Transform

Low-frequency oscillation can lead to the instability of an interconnected power system. Some power systems around the world have already seen blackout incidents because of low-frequency oscillation. Hence, identification of the low-frequency oscillation is critical to the interconnected power system. Low-frequency oscillation mode can be identified from its eigenvalue. However, it requires a true model of the large complex power system and works on the linear model under certain operating condition. The recorded signal from Phasor measurement unit (PMU) is used to apply Continuous Wavelet Transform (CWT) to identify low-frequency oscillation without prior knowledge of the complex mathematical model of the large interconnected power system. Among wavelet families, Complex Morlet mother-wavelet function is used in this work to formulate the mathematical relationship between system ringdowns low-frequency oscillation modal information and the CWT. The magnitude and phase plot of the complex-valued wavelet coefficients yield mode of the recorded signal. In this paper oscillation signal from a two-area four-machine power system is measured and then analyzed using continuous wavelet transform (CWT) technique to obtain its modal information corresponding to inter-area mode of oscillation. Finally, the linear system analysis method is used to compare the result from the proposed technique.