Oscillation Detection Algorithm Development Summary Report and Test Plan

Abstract

EXECUTIVE SUMMARYSmall signal stability problems are one of the major threats to grid stability and reliability in California and the western U.S. power grid. An unstable oscillatory mode can cause large-amplitude oscillations and may result in system breakup and largescale blackouts. There have been several incidents of system-wide oscillations. Of them, the most notable is the August 10, 1996 western system breakup produced as a result of undamped system-wide oscillations. There is a great need for real-time monitoring of small-signal oscillations in the system. In power systems, a small-signal oscillation is the result of poor electromechanical damping. Considerable understanding and literature have been developed on the small-signal stability problem over the past 50+ years. These studies have been mainly based on a linearized system model and eigenvalue analysis of its characteristic matrix. However, its practical feasibility is greatly limited because power system models have been found inadequate in describing realtime operating conditions. Significant efforts have been devoted to monitoring system oscillatory behaviors from real-time measurements in the past 20 years. The deployment of phasor measurement units (PMU) provides high-precision time-synchronized data needed for estimating oscillation modes. Measurement-based modal analysis, also known as ModeMeter, uses real-time phasor measurements to estimate system oscillation modes and their damping. Low damping indicates potential system stability issues. Oscillation alarms can be issued when the power system is lightly damped. A good oscillation alarm tool can provide time for operators to take remedial reaction and reduce the probability of a system breakup as a result of a light damping condition. To facilitate ModeMeter development and evaluation, the Western Electricity Coordinating Council (WECC) has conducted a number of system tests in the past decade. The tests include large signal tests through insertion of the 1,400 MW Chief Joseph brake resistance, mid-level signal tests through ±125 MW modulation of Pacific DC Intertie (PDCI) real power set values, and noise probing tests through ±10-20 MW modulation of the PDCI power. Recently, the system tests have advanced to a weekly basis, towards future continuous tests and real-time oscillation monitoring. Real-time oscillation monitoring requires ModeMeter algorithms to have the capability to work with various kinds of measurements: disturbance data (ringdown signals), noise probing data, and ambient data.Several measurement-based modal analysis algorithms have been developed. They include Prony analysis, Regularized Robust Recursive Least Square (R3LS) algorithm, Yule-Walker algorithm, Yule-Walker Spectrum algorithm, and the N4SID algorithm. Each has been shown to be effective for certain situations, but not as effective for some other situations. For example, the traditional Prony analysis works well for disturbance data but not for ambient data, while Yule-Walker is designed for ambient data only....

Survey on forced oscillations in power system

“…On the other hand, undamped modes can be hazardous for the power system. In the past decades, remarkable efforts has been devoted to estimate the modal properties of a power system using component-based approach and measurement-based approach [3]. Numerous measurement-based modal analysis algorithms has been proposed.…”

Stochastic subspace identification‐based approach for tracking inter‐area oscillatory modes in bulk power system utilising synchrophasor measurements

“…On the other hand, the measurement-based approaches are alternatives to resolve these issues and complement the model-based approaches [4,5]. Inspired by the initiative of the wide-area measurement systems (WAMSs) which consist of phasor measurement units (PMUs), the measurement-based approaches, also known as ModeMeter [5], are proposed to extract the electromechanical oscillatory modes and damping from the measurement. One appealing characteristics of such approaches is that they do not require detailed power system model nor accurate parameters.…”

Improved non‐linear least squares method for estimating the damping levels of electromechanical oscillations

“…a damping ratio lower than a certain threshold value) all the necessary countermeasures have to be implemented for restoring secure and stable operating conditions, for instance generators’ re‐dispatching, tie line flows adjustments, load reductions, network topology changes etc. [6]. Tracking of electromechanical oscillations can be currently performed in real time thanks to the quick development of the wide area measurement/monitoring systems (WAMS) and the development of mode meter modules to equip the traditional energy management systems (EMS).…”