Joseph Euzebe Tate

Line Outage Detection Using Phasor Angle Measurements

Although phasor measurement units (PMUs) have become increasingly widespread throughout power networks, the buses monitored by PMUs still constitute a very small percentage of the total number of system buses. Our research explores methods to derive useful information from PMU data in spite of this limited coverage. In particular, we have developed an algorithm which uses known system topology information, together with PMU phasor angle measurements, to detect system line outages. In addition to determining the outaged line, the algorithm also provides an estimate of the pre-outage flow on the outaged line. To demonstrate the effectiveness of our approach, the algorithm is demonstrated using simulated and real PMU data from two systems - a 37-bus study case and the TVA control area.

SCADA Cyber Security Testbed Development

New technologies are increasing the vulnerability of the power system to cyber security threats. Dealing with these threats and determining vulnerabilities is an important task for utilities. This paper presents the development of a testbed designed to assess the vulnerabilities introduced by using public networks for communication.

Probabilistic map of critical functional regions of the human cerebral cortex: Broca’s area revisited

The organization of basic functions of the human brain, particularly in the right hemisphere, remains poorly understood. Recent advances in functional neuroimaging have improved our understanding of cortical organization but do not allow for direct interrogation or determination of essential (versus participatory) cortical regions. Direct cortical stimulation represents a unique opportunity to provide novel insights into the functional distribution of critical epicentres. Direct cortical stimulation (bipolar, 60 Hz, 1-ms pulse) was performed in 165 consecutive patients undergoing awake mapping for resection of low-grade gliomas. Tasks included motor, sensory, counting, and picture naming. Stimulation sites eliciting positive (sensory/motor) or negative (speech arrest, dysarthria, anomia, phonological and semantic paraphasias) findings were recorded and mapped onto a standard Montreal Neurological Institute brain atlas. Montreal Neurological Institute-space functional data were subjected to cluster analysis algorithms (K-means, partition around medioids, hierarchical Ward) to elucidate crucial network epicentres. Sensorimotor function was observed in the pre/post-central gyri as expected. Articulation epicentres were also found within the pre/post-central gyri. However, speech arrest localized to ventral premotor cortex, not the classical Brocas area. Anomia/paraphasia data demonstrated foci not only within classical Wernickes area but also within the middle and inferior frontal gyri. We report the first bilateral probabilistic map for crucial cortical epicentres of human brain functions in the right and left hemispheres, including sensory, motor, and language (speech, articulation, phonology and semantics). These data challenge classical theories of brain organization (e.g. Brocas area as speech output region) and provide a distributed framework for future studies of neural networks.

Double line outage detection using phasor angle measurements

Building upon prior research in single outage detection, this work looks at how double line outages can be detected using a combination of pre-outage topology information and real-time phase angle measurements that are typically obtained from phasor measurements units (PMUs). For double line outage detection, there are two key issues which must be addressed: identification of equivalent outages and reduction of the event search space. The existence of indistinguishable outages due to incomplete PMU deployment is proved and a method of recognizing these indistinguishable outages is presented. In addition, methods for reducing the size of the multiple line outage event space are discussed.

A comparison of the optimal multiplier in polar and rectangular coordinates

Studies of the optimal multiplier (or optimal step size) modification to the standard Newton-Raphson (NR) load flow have mainly focused on highly stressed and unsolvable systems. This paper extends these previous studies by comparing performance of the NR load flow with and without optimal multipliers for a variety of unstressed, stressed, and unsolvable systems. Also, the impact of coordinate system choice in representing the voltage phasor at each bus is considered. In total, four solution methods are compared: the NR algorithm with and without optimal multipliers using polar and rectangular coordinates. This comparison is carried out by combining analysis of the optimal multiplier technique with empirical results for two-bus, 118-bus, and 10 274-bus test cases. These results indicate that the polar NR load flow with optimal multipliers is the best method of solution for both solvable and unsolvable cases.

Damping Inter-Area Oscillations Based on a Model Predictive Control (MPC) HVDC Supplementary Controller

This paper introduces, formulates and evaluates an approach for damping inter-area oscillations of power systems based on supplementary current control of a line-commutated HVDC link. The proposed control is based on the model predictive control (MPC) strategy. The salient feature of the MPC as compared with other optimal control strategies, e.g., the linear quadratic Gaussian (LQG) control, is that it adjusts the control signal to achieve the objectives while explicitly respecting the plant constraints. This paper also compares the performance of the MPC with that of the LQG control. The two approaches are tested on the Western System Coordinating Council (WSCC) 9-bus system and the IEEE 14-bus system. Small-signal disturbance and large-signal disturbance stability studies are performed to demonstrate and compare the performances of the LQG and MPC methodologies. The study results show the effective and superior performance of the MPC for damping poorly damped oscillatory modes of the test systems.

Lossless compression of synchronized phasor measurements

By reporting time-synchronized phasor magnitudes and phase angles at rates at or above the system frequency, phasor measurement units promise to dramatically increase our ability to understand both historical and real-time power system conditions. This new information does not come without a cost, however, and one potential barrier to the effective utilization of this new data source is the increased amount of information transmission and storage capability these devices require. One way to mitigate the increased storage requirements of synchrophasor data is to compress the data, although this compression should not come at the cost of reduced accuracy. This paper proposes a new method for the lossless compression of voltage magnitude and phase data in which known characteristics of the power system are used to improve upon common, off-the-shelf compression techniques. The method is evaluated with real and simulated PMU data to show its effectiveness.

Extracting steady state values from phasor measurement unit data using FIR and median filters

With the increased penetration of phasor measurement units (PMUs) within the power grid, there is a clear need for understanding the different filtering techniques which can be used to convert raw measurements into usable data. Because of the high sampling rate of PMUs, there are relatively high frequency components present in PMU signals when compared to traditional power system measurements. These components, which can range from 0.1 Hz to half the PMU sampling frequency, must be filtered out before the data can be used with steady state analysis techniques. This paper compares the performance of two different means of filtering out this higher frequency data—FIR filtering and median filtering. Several metrics are defined to quantify the behavior of these filters with a particular emphasis on handling measurements before and after system events. Results are presented based on both real and simulated PMU data. Based on these tests, observations regarding the advantages and disadvantages of the two filter types are discussed.

Parameter estimation of doubly fed induction generator driven by wind turbine

In order to reduce the environmental consequences of electric power generation, there has been a growing interest in the use of renewable resources for generating electricity. One way of generating electricity from renewable sources is to use wind turbines that convert the kinetic energy contained in the flowing air into electrical energy. As wind power is integrated in large scale European and North American power systems, investigating the dynamic behavior of these turbines is of great importance. Unfortunately, the parameters of the wind turbine needed to conduct dynamic analysis are frequently unknown or inaccurate. This paper analyzes the behavior of two Kalman filter based estimation techniques, the Extended Kalman Filter (EKF) and the Unscented Kalman Filter (UKF), for parameter estimation of the doubly fed induction generator (DFIG) driven by wind turbine. The performance of these two methods is evaluated from different aspects: estimation accuracy, computation time, and robustness to variation of the initial parameter estimates and filter gains. Our experiments show that the performance of the UKF is superior to that of the EKF.

Energy Storage System Control for Prevention of Transient Under-Frequency Load Shedding

This paper proposes and evaluates a systematic method for controlling an energy storage system for preventing load shedding due to transient declines in frequency. The proposed controller works on local measurements and uses an extended Kalman filter to perform online identification of system parameters. These results are then used to implement a model predictive controller for the safe withdrawal of support and energy recovery, both without incurring transient load shedding. The formulation accounts for single generator outages and includes power system parameters such as inertia, damping, and droop. The proposed method is evaluated using the nonlinear simulations of 6-bus and 24-bus test systems known as Roy Billinton Test System (RBTS) and IEEE Reliability Test System. The results show that the proposed controller is effective in preventing transient load shedding.