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This paper presents a new data-driven methodology for power system coherency identification of generator and non-generator buses. This methodology is exclusively based on intrinsic statistical properties extracted directly from observations, without any prior assumption of the probability distribution function (PDF) for the data. The main advances of this proposal are: (i) gathering of statistical information from the data itself despite scenarios where the PDF may change (different inverter-based load and generation scenarios, load levels of the system, and changes in topology); and (ii) assignment of buses into coherent areas without any tuning of parameters, nor manually labeling of huge amounts of training data. This new method, called typicality-based data analysis (TDA), is applied to the correlation metric of the distance between dynamic responses of buses, either voltage angles or frequencies. Simulated signals from a benchmark power system with cases considering the presence of non-synchronous generation and islanding conditions, and real data associated with generation trips in the U.S. Eastern Interconnection are used to corroborate the methodology effectiveness. [ABSTRACT FROM AUTHOR]

The paper proposes a new approach for the recovery of missing data from phasor measurement units (PMUs). The approach is based on the application of tensor decomposition to PMU data organized as three-dimensional tensors with respect to time, location and type of variables. The organization of the PMU data is in the form of a bus-oriented data structure and a branch-oriented data structure. Two versions of the approach are introduced. The first version uses polyadic tensor decomposition and the second version uses Tucker tensor decomposition. Several case studies are conducted validating the proposed approaches including measured PMU data in the New York transmission system. Comparison with existing approaches is performed to demonstrate the improvement in missing data recovery accuracy achieved by the new approach. [ABSTRACT FROM AUTHOR]

We present an energy storage controller synthesis method for power systems with respect to metric temporal logic (MTL) specifications. The power systems with both constant impedance loads and constant power loads are modeled as a set of differential–algebraic equations. After a fault is cleared, with uncertainties in the fault clearing time, the generator machine angles and rotor speed deviations will enter a set of postfault initial states. We use the robust neighborhood approach to cover this set using the initial robust neighborhoods of finitely many simulated postfault trajectories. These simulated postfault trajectories meet the frequency regulation requirements specified in MTL as they are driven by the optimal control input signals obtained through a functional gradient descent approach. In this way, all the possible postfault trajectories with the given uncertainties in the fault clearing time are guaranteed to satisfy the MTL specification. Furthermore, we learn a piecewise linear control law from the data of the simulated trajectories to generate a feedback controller. [ABSTRACT FROM AUTHOR]

Cyber data attacks are the worst-case interacting bad data to power system state estimation and cannot be detected by existing bad data detectors. This paper for the first time analyzes the likelihood of cyber data attacks by characterizing the actions of a malicious intruder in a dynamic environment, where power system state evolves with time, and measurement devices could become inaccessible due to detected attacks. This analysis is important for the operator to evaluate the vulnerability of power systems to data attacks. A Markov decision process is proposed to model an intruder’s strategy, with the objective to maximize its cumulative reward across time. The optimal attack policy is solved from the intruder’s perspective, and the attack likelihood is then analyzed based on the obtained policy. Two attack scenarios are studied to model different knowledge levels of the intruder about the dynamics of power systems. Numerical experiments are conducted on the IEEE 14-bus and 30-bus test systems to study the intruder’s attack strategy and analyze the attack probability. [ABSTRACT FROM AUTHOR]

Motivated by missing data recovery in power system monitoring, we study the problem of recovering missing entries of high-dimensional signals that exhibit low-dimensional nonlinear structures. We propose a novel model, termed as “union and sums of subspaces,” to characterize practical nonlinear datasets. In this model, each data point belongs to either one of a few low-dimensional subspaces or the sum of a subset of subspaces. We propose convex-optimization-based methods to recover missing entries under this model. We theoretically analyze the recovery guarantee of our proposed methods with both noiseless and noisy measurements. Numerical experiments on synthetic data and simulated power system data are conducted to verify the effectiveness of the proposed methods. [ABSTRACT FROM PUBLISHER]

Electromechanical wave propagation is present in power systems as a transient spatial delay of generator rotor angle variations when a disturbance occurs. The control and mitigation of the this wave phenomenon, which spreads out to different locations at a comparably slow speed, is important for enhancing power system transient stability, as shown in part two of this two-paper series. In an idealized power system consisting of infinitesimal generators and line impedances, this traveling wave can exist to infinite frequencies, its speed can be derived from a wave equation and its reflection can be eliminated by a characteristic termination. Part one of this paper series examines realistic power systems with finite size generators and line impedances. It shows that there is a finite approximation of the traveling wave in real power systems as the wave can exist only within a finite frequency range. This paper also examines aspects such as reflections due to discrete elements, controller design based on the load modulation effect, and the existence of traveling wave and its attenuation in the Australian power system. [ABSTRACT FROM AUTHOR]

This second part of a two-paper series gives an overview of key insights and control implications arising from the wave characteristics of power system transient stability. These insights, which are unique to traveling wave interpretation, are obtained through time-domain analysis of artificial and real test systems: “critical region for a stressed link near the end of a longitudinal system,” “dispersed control in a path,” “placement of controllers considering structure and load distribution in a system,” and “localized transient stability enhancement.” Good transient stability enhancement is successfully achieved by controllers in all test systems in terms of larger critical clearing time, which directly translates to increased maximum safe power transfer. The controller design is based on the transmission line analogy of traveling waves and load modulation effect. The concepts in this paper series can assist in improving the design of control strategies to enhance power system transient stability by considering the wave aspects. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

As wind penetration increases in power systems around the world, new challenges to the controllability and operation of a power system are encountered. In particular, frequency response is impacted when a considerable amount of power-electronics interfaced generation, such as wind, is connected to the system. This paper uses small-signal analysis and dynamic simulation to study frequency response in power systems and investigate how Type-3 DFAG wind turbines can impact this response on a test power system, whose frequency response is determined mainly by a frequency-regulation mode. By operating the wind turbines in a deloaded mode, a proposed pitch-angle controller is designed using a root-locus analysis. Time simulations are used to demonstrate the transient and steady-state performance of the proposed controller in the test system with 25% and 50% wind penetration. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

This paper discusses the design and usage of a Simulink-based phasor measurement unit (PMU) simulator package. The simulator and PMU data is available upon request from the first author. The motivation for developing the package is to provide a flexible environment for teaching phasor measurement and frequency estimation to advanced undergraduate and graduate students, and providing a knowledge base to students for research. This software allows for the exploration of the algorithms and phenomena involved in the phasor estimation process. The package is built on the Simulink platform and is able to process simulated signals as well as measured point-on-wave data. The popularity and relevance of the proposed package is evaluated using formal questioners. [ABSTRACT FROM PUBLISHER]