Evaluation of the ITD Based Methods and the ERA based Methods in Estimating Inter-area Electromechanical Modes During Ambient Operation

An accurate and full awareness of the properties of the interarea electromechanical oscillation modes is essential for the secure operation of the power system. This paper applies the Ibrahim time domain (ITD) method to estimate the interarea modes of the power systems, including the frequencies, damping ratios and mode shapes, using PMU measurements during ambient operation condition. Three ITD-based methods are investigated and their performances are evaluated and compared with those of the methods based on the eigen-system realization algorithm (ERA). The performance evaluation of the methods includes their robustness to the measurement noise, their sensitivity to different levels of ambient excitation and their computation efficiency. Considering the random feature of the measurement noise and the ambient excitation, Monte Carlo simulations are conducted to obtain the statistical results. Comparison results in the 16-machine power system model show that the ITD-based methods can accurately identify more interarea modes than the ERA-based methods do, and that all the three ITD-based methods are much faster than the ERA-based methods, which makes them promising for real time implementation. The proposed methods are also validated using real PMU measurements from Sichuan power grid of China.