Synchronized measurement based estimation of inter-area electromechanical modes using the Ibrahim time domain method

Abstract

Based on measured ring-down signals from the power systems, this paper introduces the Ibrahim time domain (ITD) method for estimating the inter-area electromechanical modes, including the frequencies, damping ratios and the mode shapes. A zero-phase low-pass filter is utilized to improve the performance of the ITD method in the presence of measurement noise, and the statistical characteristics of the estimation results are obtained through Monte Carlo simulations. The performance of the proposed method is compared with that of the stochastic subspace identification (SSI) technique. Simulation results show that in the presence of measurement noise, the ITD method and the SSI method have similar good performance, but the ITD method is much faster than the SSI method; and when there exit both ring-down signals and ambient noise signals (ring-downs contaminated by ambient noise), the ITD method performs better than the SSI method does. Finally, the performance of the ITD method is evaluated by considering three factors that may be encountered in real measured data, which are measurement noise, ambient noise and limited availability of PMU measurements, and we find that as long as the total participation of the available inputs in a particular mode is overwhelming, the ITD method can still give quite acceptable estimation results for this mode. All the simulations are conducted using a nonlinear power system model, and the effect of the nonlinear factors of the system is incorporated in the simulation data.