George Stefopoulos

Phasor-Measurement-Based State Estimation for Synchrophasor Data Quality Improvement and Power Transfer Interface Monitoring

Validation and data quality improvement of phasor data through state estimation is the first step in ensuring that the synchrophasor data is useful for applications in monitoring, visualization, and control. This paper presents a phasor-measurement-based state estimator (PSE) for improving data consistency by identifying angle biases and current scaling errors in the phasor data using the augmented state vector approach. These errors can arise from issues with the Global Positioning Signal (GPS), timing circuits, instrument channels, and/or data channel scaling. The PSE is demonstrated using several sets of disturbance data from the Central New York Power System. The PSE can also provide estimates of line parameters and transformer tap ratios with sufficient measurement redundancy. Finally, the PSE allows the computation of interface power flows for disturbance and stability monitoring.

Missing Data Recovery by Exploiting Low-Dimensionality in Power System Synchrophasor Measurements

This paper presents a new framework of recovering missing synchrophasor measurements (erasures). Leveraging the approximate low-rank property of phasor measurement unit (PMU) data, we connect the problem of recovering PMU data erasures with recent advances in low-rank matrix completion methods. Since the existing analysis for matrix completion methods assumes an independent-erasure model that does not capture the correlations in PMU erasures, we propose two models to characterize the temporal and the channel correlations in PMU erasures and provide theoretical guarantees of a matrix completion method in recovering correlated erasures in both models. We also propose an online algorithm that can fill in the missing PMU measurements for real-time applications. Numerical experiments on actual PMU data are conducted to verify the effectiveness of the proposed methods.

Object-oriented 3-Phase distributed dynamic state estimator

This paper presents a suite of two distributed dynamic state estimators (QSE and DSE) that are performed at the substation level. The algorithm uses local GPS-synchronized and conventional non-synchronized measurements in the substation of interest for estimating the states of the substation as well as the states at the other ends of the transmission lines at the adjacent substations. The estimation algorithm provides the true dynamic (transient) states of the system. As such it provides the basic infrastructure for highly accurate real time dynamic monitoring and control at speeds that are not presently available. Numerical experiments on the NYPA Gilboa-Blenheim substation are presented in this paper for the purpose of evaluating the performance of the proposed algorithms. It is shown that the proposed algorithm is reliable and feasible for practical implementation.

Application of a Phasor-Only State Estimator to a Large Power System Using Real PMU Data

This paper applies a phasor-only state estimator (PSE) to a large power system consisting of two control regions, using synchrophasor data from 56 765/345/230 kV substations. Although the technique has been previously developed, this paper describes a topology processor to determine the redundant clusters of connected buses such that the PSE can be used in real time. This PSE allows corrections for phase biases, transformer taps, and current magnitude scaling. The ability to simultaneously solve the PSE for the two control regions is due to a PMU monitoring a tie-line between these two regions. The results show that with this method, the total vector errors of the measured voltage phasor data in these two control regions average to less than 0.5% under ambient conditions. The PSE also computes virtual phasor measurements on 70 buses that do not have PMUs, including large steam generator and wind-turbine generator substations.

Identification of Successive “Unobservable” Cyber Data Attacks in Power Systems Through Matrix Decomposition

This paper presents a new framework of identifying a series of cyber data attacks on power system synchrophasor measurements. We focus on detecting “unobservable” cyber data attacks that cannot be detected by any existing method that purely relies on measurements received at one time instant. Leveraging the approximate low-rank property of phasor measurement unit (PMU) data, we formulate the identification problem of successive unobservable cyber attacks as a matrix decomposition problem of a low-rank matrix plus a transformed column-sparse matrix. We propose a convex-optimization-based method and provide its theoretical guarantee in the data identification. Numerical experiments on actual PMU data from the Central New York power system and synthetic data are conducted to verify the effectiveness of the proposed method.

Identification of “unobservable” cyber data attacks on power grids

This paper presents a new framework of identifying cyber data attacks on synchrophasor measurements. We focus on detecting “unobservable” cyber data attacks that cannot be detected by any existing detection method that purely relies on measurements received at one time instant. Leveraging the approximate low-rank property of phasor measurement unit (PMU) data, we formulate the unobservable cyber attack identification problem as a matrix decomposition problem where the observed data matrix is the sum of a low-rank matrix plus a linear projection of a column-sparse matrix. We propose a convex-optimization-based decomposition method and provide its theoretical guarantee in the attack identification. Numerical experiments on actual PMU data and synthetic data are conducted to verify the effectiveness of the proposed method.

Inter-area oscillation damping and primary frequency control of the New York state power grid with multi-functional multi-band power system stabilizers

The paper discusses the impacts of the advanced closed loop control through multi-functional multi-band power system stabilizers on dynamic performance of the New York State power grid. Reference signal modulation of certain devices in the system has been shown to improve system damping and affect frequency response during generator outage scenarios. The methodology behind the development of system models and subsequent tuning of the controllers is discussed. Results demonstrate how feedback control of various power system equipment, including those that are electronically-interfaced, can aid in improving dynamic behavior of large interconnected systems.

Advanced disturbance recording and playback enabled by a distributed dynamic state estimation including bad data detection and topology change identification

Previous work has demonstrated a distributed dynamic state estimator (DSE) that is implemented in the substation level using local data (synchronized and non-synchronized) and can capture in real time the dynamics of the system with speeds of 60 times per second. Due to the plurality of the available measurements in a substation, bad data is a common occurrence. This paper initially focuses on the algorithm based on which the DSE identifies and removes bad data. Topology changes can also be identified and the system model is automatically updated in the DSE procedure. The end result is a highly accurate and validated model of the system which can be efficiently stored and utilized offline, thus enabling a novel scheme for disturbance recording and playback. Numerical results on the bad data and topology identification, performed on the NYPA Gilboa-Blenheim substation, are presented. A demonstration of the disturbance recording and playback tool is also provided.

Phasor-measurement-based voltage stability margin calculation for a power transfer interface with multiple injections and transfer paths

For complex power transfer interfaces or load areas with multiple in-feeds, we present a method for phasor-measurement-based calculation of voltage stability margins. In the case of complex transfer paths with multiple injections, a radial system approach may not be sufficient for voltage stability analysis. Our approach provides voltage stability margins considering the full fidelity of the transfer paths. In this paper, we extend a previously proposed phasor-measurement-based approach [1] and apply it to a voltage stability-limited power transfer interface using synchronized phasor measurements from loss-of-generation disturbance events. Previous work employed a simple radial system [2] or modeled a power transfer interface using only one generator [1]. In our approach, we use the PMU data to model multiple external injections that share the power transfer increase, and we employ a modified AQ-bus power flow method to compute the steady-state voltage stability margins [3]. We demonstrate the method using real PMU data from disturbance events in the US Eastern Interconnection.

Validation of generic models for stability analysis of two large static var systems in New York using PMU data

This paper presents an approach for the validation of generic standard models for an SVC and a STATCOM using voltage and current data measured by phasor measurement units (PMUs) at the respective substations where these devices are installed. The data used were recorded in real-time during system disturbances at different locations of the system. By using the measured voltage, as an input to the model, the response of the model is computed and compared with the measured response of the shunt dynamic device. An optimization algorithm is used to optimally estimate the gains of the modeled controls in order to achieve good agreement between the simulated and measured response of the device. The models used in this process are generic models for static var systems developed in previous work by the WECC SVC Task Force.