| 1. |
- Almas, Muhammad Shoaib, 1987-
(author)
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Synchrophasor Applications and their Vulnerability to Time Synchronization Impairment
- 2017
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Doctoral thesis (other academic/artistic)abstract
- Recent years have seen the significance of utilizing time-synchronized, high resolution measurements from phasor measurement units (PMUs) to develop and implement wide-area monitoring, protection and control (WAMPAC) systems. WAMPAC systems aim to provide holistic view of the power system and enable detection and control of certain power system phenomena to enhance reliability and integrity of the grid.This thesis focuses on the design, development and experimental validation of WAMPAC applications, and investigates their vulnerability to time synchronization impairment. To this purpose, a state-of-the-art real-time hardware-in-the-loop (RT-HIL) test-bench was established for prototyping of synchrophasor-based applications. This platform was extensively used throughout the thesis for end-to-end testing of the proposed WAMPAC applications. To facilitate the development of WAMPAC applications, an open-source real-time data mediator is presented that parses the incoming synchrophasor stream and provides access to raw data in LabVIEW environment.Within the domain of wide-area protection applications, the thesis proposes hybrid synchrophasor and IEC 61850-8-1 GOOSE-based islanding detection and automatic synchronization schemes. These applications utilize synchrophasor measurements to assess the state of the power system and initiate protection / corrective action using GOOSE messages. The associated communication latencies incurred due to the utilization of synchrophasors and GOOSE messages are also determined. It is shown that such applications can have a seamless and cost-effective deployment in the field. Within the context of wide-area control applications, this thesis explores the possibility of utilizing synchrophasor-based damping signals in a commercial excitation control system (ECS). For this purpose, a hardware prototype of wide-area damping controller (WADC) is presented together with its interface with ECS. The WADC allows real-time monitoring and remote parameter tuning that could potentially facilitate system operators’ to exploit existing damping assets (e.g. conventional generators) when changes in operating conditions or network topology emerges.Finally the thesis experimentally investigates the impact of time synchronization impairment on WAMPAC applications by designing RT-HIL experiments for time synchronization signal loss and time synchronization spoofing. It is experimentally demonstrated that GPS-based time synchronization impairment results in corrupt phase angle computations by PMUs, and the impact this has on associated WAMPAC application.
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| 2. |
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| 3. |
- Barreto, Sergio, et al.
(author)
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Undetectable PMU Timing-Attack on Linear State-Estimation by UsingRank-1 Approximation
- 2018
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In: IEEE Transactions on Smart Grid. - : IEEE Press. - 1949-3053 .- 1949-3061. ; 9:4, s. 3530-3542
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Journal article (peer-reviewed)abstract
- Smart-grid applications based on synchrophasor measurements have recently been shown to be vulnerable to timing attacks. A fundamental question is whether timing attacks could remain undetected by bad-data detection algorithms used in conjunction with state-of-the-art situational-awareness state estimators. In this paper, we analyze the detectability of timing attacks on linear state-estimation. We show that it is possible to forge delay attacks that are undetectable. We give a closed form for an undetectable attack; it imposes two phase offsets to two or more synchrophasor-based measurement units that can be translated to synchrophasors’ time delays. We also propose different methods for combining two-delays attacks to produce a larger impact. We simulate the attacks on a benchmark powertransmission grid, we show that they are successful and can lead to physical grid damage. To prove undetectability, we use classic bad-data detection techniques such as the largest normalized residual and the 2-test.
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| 4. |
- Delcourt, Marguerite, et al.
(author)
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Time-Synchronization Attack Detection in Unbalanced Three-Phase Systems
- 2021
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In: IEEE Transactions on Smart Grid. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1949-3053 .- 1949-3061. ; 12:5, s. 4460-4470
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Journal article (peer-reviewed)abstract
- Phasor measurement units (PMU) rely on an accurate time-synchronization to phase-align the phasors and timestamp the voltage and current phasor measurements. Among the symmetrical components computed from the phasors in three-phase systems, the standard practice only uses the direct-sequence component for state estimation and bad data detection (BDD). Time-synchronization attacks (TSAs) can compromise the measured phasors and can, thus, significantly alter the state estimate in a manner that is undetectable by widely used power-system BDD algorithms. In this paper we investigate the potential of utilizing the three-phase model instead of the direct-sequence model for mitigating the vulnerability of state estimation to undetectable TSAs. We show analytically that if the power system is unbalanced then the use of the three-phase model as input to BDD algorithms enables to detect attacks that would be undetectable if only the direct-sequence model was used. Simulations performed on the IEEE 39-bus benchmark using real load profiles recorded on the grid of the city of Lausanne confirm our analytical results. Our results provide a new argument for the adoption of three-phase models for BDD, as their use is a simple, yet effective measure for reducing the vulnerability of PMU measurements to TSAs.
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| 5. |
- Mahmood, Farhan, et al.
(author)
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Experimental Validation of a Steady State Model Synthesis Method for a Three-Phase Unbalanced Active Distribution Network Feeder
- 2018
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In: IEEE Access. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2169-3536. ; 6, s. 4042-4053
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Journal article (peer-reviewed)abstract
- This paper presents the field validation of a method that performs steady-state model synthesis (SSMS) of active distribution networks using syncrophasor measurements. The validation is performed by applying the SSMS method on a real active distribution feeder network by utilizing the measurements from real phasor measurement units (PMUs) installed at the EPFL campus. An extended version of total vector error and a power flow comparison at the PMU buses are used as performance assessment metrics. A real-time hardware-in-the-loop simulations set up at the Distributed Energy System Laboratory is used for further performance assessment of the SSMS application. The effectiveness of the SSMS application is demonstrated by testing it extensively for several different case studies.
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| 6. |
- Paolone, Giovanna, et al.
(author)
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Long-Term, Targeted Delivery of GDNF from Encapsulated Cells Is Neuroprotective and Reduces Seizures in the Pilocarpine Model of Epilepsy
- 2019
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In: The Journal of Neuroscience : the official journal of the Society for Neuroscience. - 1529-2401. ; 39:11, s. 2144-2156
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Journal article (peer-reviewed)abstract
- Neurotrophic factors are candidates for treating epilepsy, but their development has been hampered by difficulties in achieving stable and targeted delivery of efficacious concentrations within the desired brain region. We have developed an encapsulated cell technology that overcomes these obstacles by providing a targeted, continuous, de novo synthesized source of high levels of neurotrophic molecules from human clonal ARPE-19 cells encapsulated into hollow fiber membranes. Here we illustrate the potential of this approach for delivering glial cell line-derived neurotrophic factor (GDNF) directly to the hippocampus of epileptic rats. In vivo studies demonstrated that bilateral intrahippocampal implants continued to secrete GDNF that produced high hippocampal GDNF tissue levels in a long-term manner. Identical implants robustly reduced seizure frequency in the pilocarpine model. Seizures were reduced rapidly, and this effect increased in magnitude over 3 months, ultimately leading to a reduction of seizures by 93%. This effect persisted even after device removal, suggesting potential disease-modifying benefits. Importantly, seizure reduction was associated with normalized changes in anxiety and improved cognitive performance. Immunohistochemical analyses revealed that the neurological benefits of GDNF were associated with the normalization of anatomical alterations accompanying chronic epilepsy, including hippocampal atrophy, cell degeneration, loss of parvalbumin-positive interneurons, and abnormal neurogenesis. These effects were associated with the activation of GDNF receptors. All in all, these results support the concept that the implantation of encapsulated GDNF-secreting cells can deliver GDNF in a sustained, targeted, and efficacious manner, paving the way for continuing preclinical evaluation and eventual clinical translation of this approach for epilepsy.SIGNIFICANCE STATEMENT Epilepsy is one of the most common neurological conditions, affecting millions of individuals of all ages. These patients experience debilitating seizures that frequently increase over time and can associate with significant cognitive decline and psychiatric disorders that are generally poorly controlled by pharmacotherapy. We have developed a clinically validated, implantable cell encapsulation system that delivers high and consistent levels of GDNF directly to the brain. In epileptic animals, this system produced a progressive and permanent reduction (>90%) in seizure frequency. These benefits were accompanied by improvements in cognitive and anxiolytic behavior and the normalization of changes in CNS anatomy that underlie chronic epilepsy. Together, these data suggest a novel means of tackling the frequently intractable neurological consequences of this devastating disorder.
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| 7. |
- Shereen, Ezzeldin, et al.
(author)
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Feasibility of Time-Synchronization Attacks Against PMU-Based State Estimation
- 2020
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In: IEEE Transactions on Instrumentation and Measurement. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9456 .- 1557-9662. ; 69:6, s. 3412-3427
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Journal article (peer-reviewed)abstract
- The emerging measurement technology of phasor measurement units (PMUs) makes it possible to estimate the state of electrical grids in real time, thus opening the way to new protection and control applications. PMUs rely on precise time synchronization; therefore, they are vulnerable to time-synchronization attacks (TSAs), which alter the measured voltage and current phases. In particular, undetectable TSAs pose a significant threat as they lead to an incorrect but credible estimate of the system state. Prior work has shown that such attacks exist against pairs of PMUs, but they do not take into consideration the clock adjustment performed by the clock servo, which can modify the attack angles and make the attacks detectable. This cannot be easily addressed with the existing attacks, as the undetectable angle values form a discrete set and cannot be continuously adjusted as would be required to address the problems posed to the attacker by the clock servo. Going beyond prior work, this article first shows how to perform undetectable attacks against more than two PMUs, so that the set of undetectable attacks forms a continuum and supports small adjustments. Second, it shows how an attacker can anticipate the operation of the clock servo while achieving her attack goal and remaining undetectable. Third, this article shows how to identify vulnerable sets of PMUs. Numerical results on the 39-bus IEEE benchmark system illustrate the feasibility of the proposed attack strategies.
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| 8. |
- Theethayi, Nelson, et al.
(author)
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External Impdeance and Admittance of Buried Horizontal Wires for Transient Studies Using Transmission Line Analysis
- 2007
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In: IEEE transactions on dielectrics and electrical insulation. - 1070-9878 .- 1558-4135. ; 14:3, s. 751-761
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Journal article (peer-reviewed)abstract
- The paper investigates the applicability of some closed form expressions for the ground impedance and ground admittance of buried horizontal wires (bare and insulated) for lightning or switching transient analyses based on transmission line (TL) theory. In view of the frequency contents that typically characterize such transients, the behavior of the ground impedance and admittance is studied for a wide frequency range up to 10 MHz. Low frequency approximation of the ground impedance is not always appropriate for transient analysis. Sensitivity analyses show that, unlike overhead wires, the ground impedance for buried wires is little sensitive to the ground conductivity. On the other hand, the ground admittance varies strongly with the ground conductivity. The paper also discusses the results of transient analysis of buried cables performed by means of electromagnetic transient programs (EMTP) that neglect the ground admittance. The limits of such an approximation are discussed in order to evaluate the applicability of EMTP-like programs to the transient analysis of buried conductors. Transient pulse propagation in time domain based on finite difference time domain (FDTD) method of solution of TL equations is also discussed for a future inclusion of non-linear phenomena, like soil ionization and arcing/breakdown mechanisms, in the soil. The analysis presented could be useful in estimating surge propagation characteristics of buried wires for appropriate insulation coordination and transient protection.
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| 9. |
- Yuan, Zhao, 1988-
(author)
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Convex Optimal Power Flow Based on Second-Order Cone Programming: Models, Algorithms and Applications
- 2018
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Doctoral thesis (other academic/artistic)abstract
- Optimal power flow (OPF) is the fundamental mathematical model to optimally operate the power system. Improving the solution quality of OPF can help the power industry save billions of dollars annually. Past decades have witnessed enormous research efforts on OPF since J. Carpentier proposed the fully formulated alternating current OPF (ACOPF) model which is nonconvex. This thesis proposes three convex OPF models (SOC-ACOPF) based on second-order cone programming (SOCP) and McCormick envelope. The underlying idea of the proposed SOC-ACOPF models is to drop assumptions of the original SOC-ACOPF model by convex relaxation and approximation methods. A heuristic algorithm to recover feasible OPF solution from the relaxed solution of the proposed SOC-ACOPF models is developed. The quality of solutions with respect to global optimum is evaluated using MATPOWER and LINDOGLOBAL. A computational comparison with other SOC-ACOPF models in the literature is also conducted. The numerical results show robust performance of the proposed SOC-ACOPF models and the feasible solution recovery algorithm. We then propose to speed up solving large-scale SOC-ACOPF problem by decomposition and parallelization. We use spectral factorization to partition large power network to multiple subnetworks connected by tie-lines. A modified Benders decomposition algorithm (M-BDA) is proposed to solve the SOC-ACOPF problem iteratively. Taking the total power output of each subnetwork as the complicating variable, we formulate the SOC-ACOPF problem of tie-lines as the master problem and the SOC-ACOPF problems of the subnetworks as the subproblems in the proposed M-BDA. The feasibility of the proposed M-BDA is analytically proved. A GAMS grid computing framework is designed to compute the formulated subproblems in parallel. The numerical results show that the proposed M-BDA can solve large-scale SOC-ACOPF problem efficiently. Accelerated M-BDA by parallel computing converges within few iterations.Finally, various applications of our SOC-ACOPF models and M-BDA including distribution locational marginal pricing (DLMP), wind power integration and ultra-large-scale power network or super grid operation are demonstrated.
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