Power system low frequency oscillation mode estimation using wide area measurement systems

Abstract

Oscillations in power systems are triggered by a wide variety of events. The system damps most of the oscillations, but a few undamped oscillations may remain which may lead to system collapse. Therefore low frequency oscillations inspection is necessary in the context of recent power system operation and control. Ringdown portion of the signal provides rich information of the low frequency oscillatory modes which has been taken into analysis. This paper provides a practical case study in which seven signal processing based techniques i.e. Prony Analysis (PA), Fast Fourier Transform (FFT), S-Transform (ST), Wigner-Ville Distribution (WVD), Estimation of Signal Parameters by Rotational Invariance Technique (ESPRIT), Hilbert-Huang Transform (HHT) and Matrix Pencil Method (MPM) were presented for estimating the low frequency modes in a given ringdown signal. Preprocessing of the signal is done by detrending. The application of the signal processing techniques is illustrated using actual wide area measurement systems (WAMS) data collected from four different Phasor Measurement Unit (PMU) i.e. Dadri, Vindyachal, Kanpur and Moga which are located near the recent disturbance event at the Northern Grid of India. Simulation results show that the seven signal processing technique (FFT, PA, ST, WVD, ESPRIT, HHT and MPM) estimates two common oscillatory frequency modes (0.2, 0.5) from the raw signal. Thus, these seven techniques provide satisfactory performance in determining small frequency modes of the signal without losing its valuable property. Also a comparative study of the seven signal processing techniques has been carried out in order to find the best one. It was found that FFT and ESPRIT gives exact frequency modes as compared to other techniques, so they are recommended for estimation of low frequency modes. Further investigations were also carried out to estimate low frequency oscillatory mode with another case study of Eastern Interconnect Phasor Project (EIPP) data with the seven signal processing techniques (FFT, PA, ST, WVD, ESPRIT, HHT and MPM). It was found from the simulation results of EIPP data that two low frequency oscillatory mode (0.51Hz, 0.2Hz) exist.