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Qi, Li. "AC system stability analysis and assessment for Shipboard Power Systems." Texas A&M University, 2004. http://hdl.handle.net/1969.1/3128.
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The electric power systems in U.S. Navy ships supply energy to sophisticated systems for weapons, communications, navigation and operation. The reliability and survivability of a Shipboard Power System (SPS) are critical to the mission of a Navy ship, especially under battle conditions. When a weapon hits the ship in the event of battle, it can cause severe damage to the electrical systems on the ship. Researchers in the Power System Automation Laboratory (PSAL) at Texas A&M University have developed methods for performing reconfiguration of SPS before or after a weapon hit to reduce the damage to SPS. Reconfiguration operations change the topology of an SPS. When a system is stressed, these topology changes and induced dynamics of equipment due to reconfiguration might cause voltage instability, such as progressive voltage decreases or voltage oscillations. SPS stability thus should be assessed to ensure the stable operation of a system during reconfiguration.
In this dissertation, time frames of SPS dynamics are presented. Stability problems during SPS reconfiguration are classified as long-term stability problems. Since angle stability is strongly maintained in SPS, voltage stability is studied in this dissertation for SPS stability during reconfiguration. A test SPS computer model, whose simulation results were used for stability studies, is presented in this dissertation. The model used a new generalized methodology for modeling and simulating ungrounded stiffly grounded power systems.
This dissertation presents two new indices, a static voltage stability index (SVSILji) and a dynamic voltage stability index (DVSI), for assessing the voltage stability in static and dynamic analysis. SVSILji assesses system stability by all lines in SPS. DVSI detects local bifurcations in SPS. SVSILji was found to be a better index in comparison with some indices in the literature for a study on a two-bus power system. Also, results of DVSI were similar to the results of conventional bifurcation analysis software when applied to a small power system. Using SVSILji and DVSI on the test SPS computer model, three of four factors affection voltage stability during SPS reconfiguration were verified. During reconfiguration, SVSILji and DVSI are used together to assess SPS stability.
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Wildrick, Carl M. "Stability of distributed power supply systems." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-07112009-040311/.
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Keskin, Mehmet B. "Continuation Power Flow And Voltage Stability In Power Systems." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608718/index.pdf.
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This thesis investigates an important power system phenomenon, voltage stability, by using continuation power flow method. Voltage collapse scenario is presented which can be a serious result of voltage instability and the parameters that affect voltage collapse are discussed.
In analyzing power system voltage stability, continuation power flow method is utilized which consists of successive load flows. This method is applied to a sample test system and Turkish Power System and load-voltage curves for several buses are obtained.
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Gnanam, Gnanaprabhu. "Optimal power flow including voltage stability." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1996. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/mq25844.pdf.
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Matos, Bruna Krasota. "Finite-time stability of switched systems with application to power system stability problems." reponame:Repositório Institucional da UFPR, 2015. http://hdl.handle.net/1884/45688.
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Supervisor : Prof. Dr. Roman Kuiava<br>Dissertação (mestrado) - Universidade Federal do Paraná, Setor de Tecnologia, Programa de Pós-Graduação em Engenharia Elétrica. Defesa: Curitiba, 30/08/2016<br>Inclui referências : f. 79-82<br>Área de concentração<br>Resumo: O conceito de estabilidade a tempo finito (ETF) foi criado em 1950. Sistemas dinâmicos cujas trajetórias convergem para o estado de equilíbrio em um tempo finito fazem parte desse conceito. Sistemas chaveados lineares não homogêneos também estõ sendo considerados. Esses sistemas são oriundos de muitas aplicações de controle e para casos aonde sistemas físicos não são descritos por processos unicamente contínuos ou unicamente discretos. Essa dissertação esta concentrada no problema de estabilidade a tempo finito de uma classe de sistemas chaveados lineares não homogêneos contínuos no tempo sob um sinal de chaveamento dependente do tempo seguindo um tempo de permanência T. Uma vez que a estabilidade a tempo finito é garantida, um dos principais resultados dessa dissertação garante que qualquer trajetória do sistema que comece em uma região 1 do espaço de estados, permanecera dentro de 2 _ 1 ao longo de um intervalo de tempo finito, e para qualquer sequencia de chaveamento com tempo de estabelecimento ¯ T _ T. As condições de estabilidade a tempo finito obtidas na forma de inequações matriciais bilineares (BMIs), podem ser transformadas em inequações matriciais lineares (LMIs) por uma sequência de passos que incluem o cálculo dos conjuntos 1 e 2 por meio de um conhecimento prévio dos limites de operação do sistema. Dois exemplos ilustrativos do estudo de estabilidade em sistemas de potência são utilizados para apresentar a validade dos resultados. Palavras-chave: estabilidade a tempo finito, sistemas chaveados não autônomos, inequações matriciais lineares<br>Abstract: The finite-time stability (FTS) concept was created in the 1950. Dynamical systems whose trajectories converge to an equilibrium state in finite time are involved in this concept. Switched non-homogeneous linear systems are being considered. These systems can result from many control applications and for cases where physical systems are not described by simply continuous or simply discrete processes. This dissertation is concerned with the finite-time stability problem of a class of linear continuous-time non-homogeneous switched systems under a time-dependent switching signal constrained by a dwell-time T. Once the finite-time stability is guaranteed, one of the main results of the dissertation guarantees that any system trajectory starting in a subset 1 of the state-space will remain in 2 _ 1 over a finite time interval, and, for any switching sequence with a dwell-time ¯ T _ T. The finite-time stability conditions which provided in the form of bilinear matrix inequalities (BMIs), can be transformed to linear matrix inequalities (LMIs) by means of a step-by-step procedure that includes the computation of the sets 1 and 2 by the knowledge of the system's operating range. Two illustrative examples in power system stability study are used to show the validity of the results. Keywords: finite-time stability, Non-autonomous switched systems, Linear matrix inequalities
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Lee, Hau Aik Denis. "Voltage and power stability of HVDC systems /." Stockholm, 1998. http://www.lib.kth.se/abs98/lee0311.pdf.
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PALOMINO, EDGARDO GUILLERMO CAMACHO. "VOLTAGE STABILITY REINFORCEMENT ON ELETRIC POWER SYSTEMS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2002. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=2699@1.
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CENTRO DE PESQUISA DE ENERGIA ELÉTRICA<br>Na medida em que as redes de transmissão de energia
elétrica ficaram mais malhadas, os limites térmicos de
linhas e transformadores passaram a restringir menos a
transmissão de potência. Similarmente, o uso de sistemas
estáticos de compensação de potência reativa e
estabilizadores na excitação dos geradores aumentou a
capacidade de transmissão de potência nos sistemas antes
limitados por problemas de estabilidade angular. Hoje as
linhas de transmissão estão mais carregadas e isto deu
origem ao problema da instabilidade de tensão.Neste
trabalho, as condições de estabilidade de tensão são
avaliadas por condições nodais associadas ao máximo fluxo
de potência ativa e reativa que pode ser transmitida dos
geradores para as cargas. Estas condições nodais são
avaliadas por uma ferramenta analítica com base em
modelo matemático, simples mas poderoso, de uma direta
interpretação física do fenômeno.Índices abrangentes e
significativos são obtidos a partir da matriz Jacobiano do
sistema. Eles indicam a região de operação na curva V x P,
Q , a margem em MVA para o máximo carregamento, a
importância relativa entre as barras, uma medida de
dificuldade de transmissão, e o índice de influência que
relaciona as margens de potência entre dois pontos de
operação, o que caracteriza a eficácia ou não, por exemplo,
de uma ação de controle. O método proposto nesta tese para
reforçar as condições de estabilidade de tensão consiste de
três etapas seqüenciais. Primeiramente, avalia-se as
condições de estabilidade de tensão determinando-se a barra
crítica da rede através do cálculo da margem de potência.
Determinase o caminho de transmissão crítico, conceito novo
usado neste trabalho, entre os vários existentes para
transportar potência de geradores para aquela barra
crítica. Determina-se então o ramo crítico deste caminho,
conceito introduzido neste trabalho. Um programa de fluxo de
potência ótimo é usado para aliviar o carregamento desse
ramo crítico. A seqüência começa novamente com a avaliação
das condições no novo ponto de operação. Todas as etapas são
repetidas até que as margens resultantes sejam julgadas
adequadas.Barras de carga, de geração e de tensão
controlada por compensadores de potência reativa em
paralelo com a rede podem ser eleitas como a barra crítica.
Somente o método de avaliação nodal usado é capaz de lidar
com qualquer tipo de barra. Da mesma forma, o procedimento
proposto para reforçar as condições de estabilidade de
tensão é adequado para qualquer tipo de barra.São mostrados
inúmeros testes, tanto ilustrativos como com sistemas
reais, em pontos de operação também reais, inclusive na
situação de iminente colapso de tensão. Verifica-se que o
método proposto realmente produz os resultados desejados.<br>As the electric power transmission networks became more
interconnected, the thermal limits of lines and
transformers restrict less the power transmission.
Similarly, the use of static systems of reactive power
compensation increases the power transmission capacity in
systems whereas before they were limited by problems of
angular stability. Actually, transmission lines are more
loaded and create the voltage stability problem.
In this work, voltage stability conditions are assessment
by nodal conditions associated to the maximum active and
reactive power flow that can be transmitted from generators
to loads.These nodal conditions are assessment using an
analytical tool, based on a simple but sound mathematical
background, modelling a straightforward physical
haracterisation of the phenomena. Comprehensive and
meaningful indices are obtained from system Jacobean matrix.
They indices indicate the operating region in V x P,Q
curve, the MVA margin to the maximum load, the relative
importance among buses, the buses loading ranking, a
measure of difficult for power transmission, and the
influence indices that relates power margins between two
operating points, which characterises efficiency or not,
for example, of a control action.In order to reinforce
voltage stability condition, the thesis proposes a method
consisting of three sequential stages. Firstly, voltage
stability is analysed, deciding network critical bus using
the power margin calculation. Next, the critical
transmission path is decided, which is a new concept used
in this work, in between several existing used to transport
generators power for that critical bus. Then, critical
branch is obtained through this path, concept introduced in
this work. An optimal power flow program is used to
alleviate load flow in the critical branch. The sequence
starts again with the stability condition assessment in the
new operating point. All stages are repeated until
resultant margins are judged suitable. Load, generation and
voltage-controlled bus by shunt reactive power compensators
could be considered critical bus. The nodal method used is
the only one capable of handling any bus type.Several cases
are shown, illustrative as well as real systems using real
operating points,including imminent voltage collapse
situations. It is verified that the proposed method really
produces the desired results.
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Nguyen, Hung Dinh. "Robust stability assessment for future power systems." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/115726.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.<br>Cataloged from PDF version of thesis. "Due to the condition of the original material, there are unavoidable flaws in this reproduction. Some pages in the original document contain text that is illegible"--Disclaimer Notice page.<br>Includes bibliographical references (pages 119-128).<br>Loss of stability in electrical power systems may eventually lead to blackouts which, despite being rare, are extremely costly. However, ensuring system stability is a non-trivial task for several reasons. First, power grids, by nature, are complex nonlinear dynamical systems, so assessing and maintaining system stability is challenging mainly due to the co-existence of multiple equilibria and the lack of global stability. Second, the systems are subject to various sources of uncertainties. For example, the renewable energy injections may vary depending on the weather conditions. Unfortunately, existing security assessment may not be sufficient to verify system stability in the presence of such uncertainties. This thesis focuses on new scalable approaches for robust stability assessment applicable to three main types of stability, i.e., long-term voltage, transient, and small-signal stability. In the first part of this thesis, I develop a novel computationally tractable technique for constructing Optimal Power Flow (OPF) feasibility (convex) subsets. For any inner point of the subset, the power flow problem is guaranteed to have a feasible solution which satisfies all the operational constraints considered in the corresponding OPF. This inner approximation technique is developed based on Brouwer's fixed point theorem as the existence of a solution can be verified through a self-mapping condition. The self-mapping condition along with other operational constraints are incorporated in an optimization problem to find the largest feasible subsets. Such an optimization problem is nonlinear, but any feasible solution will correspond to a valid OPF feasibility estimation. Simulation results tested on several IEEE test cases up to 300 buses show that the estimation covers a substantial fraction of the true feasible set. Next, I introduce another inner approximation technique for estimating an attraction domain of a post-fault equilibrium based on contraction analysis. In particular, I construct a contraction region where the initial conditions are "forgotten", i.e., all trajectories starting from inside this region will exponentially converge to each other. An attraction basin is constructed by inscribing the largest ball in the contraction region. To verify contraction of a Differential-Algebraic Equation (DAE) system, I also show that one can rely on the analysis of extended virtual systems which are reducible to the original one. Moreover, the Jacobians of the synthetic systems can always be expressed in a linear form of state variables because any polynomial system has a quadratic representation. This makes the synthetic system analysis more appropriate for contraction region estimation in a large scale. In the final part of the thesis, I focus on small-signal stability assessment under load dynamic uncertainties. After introducing a generic impedance-based load model which can capture the uncertainty, I propose a new robust small signal (RSS) stability criterion. Semidefinite programming is used to find a structured Lyapunov matrix, and if it exists, the system is provably RSS stable. An important application of the criterion is to characterize operating regions which are safe from Hopf bifurcations. The robust stability assessment techniques developed in this thesis primarily address the needs of a system operator in electrical power systems. The results, however, can be naturally extended to other nonlinear dynamical systems that arise in different fields such as biology, biomedicine, economics, neuron networks, and optimization. As the robust assessment is based on sufficient conditions for stability, there is still room for development on reducing the inevitable conservatism. For example, for OPF feasibility region estimation, an important open question considers what tighter bounds on the nonlinear residual terms one can use instead of box type bounds. Also, for attraction basin problem, finding the optimal norms and metrics which result in the largest contraction domain is an interesting potential research question.<br>by Hung Dinh Nguyen.<br>Ph. D.
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Vance, Katelynn Atkins. "Evaluation of Stability Boundaries in Power Systems." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/78322.
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Power systems are extremely non-linear systems which require substantial modeling and control efforts to run continuously. The movement of the power system in parameter and state space is often not well understood, thus making it difficult or impossible to determine whether the system is nearing instability. This dissertation demonstrates several ways in which the power system stability boundary can be calculated. The power system movements evaluated here address the effects of inter-area oscillations on the system which occur in the seconds to minutes time period.
The first uses gain scheduling techniques through creation of a set of linear parameter varying (LPV) systems for many operating points of the non-linear system. In the case presented, load and line reactance are used as parameters. The scheduling variables are the power flows in tie lines of the system due to the useful information they provide about the power system state in addition to being available for measurement. A linear controller is developed for the LPV model using H₂/H∞ with pole placement objectives. When the control is applied to the non-linear system, the proposed algorithm predicts the response of the non-linear system to the control by determining if the current system state is located within the domain of attraction of the equilibrium. If the stability domain contains a convex combination of the two points, the control will aid the system in moving towards the equilibrium.
The second contribution of this thesis is through the development and implementation of a pseudo non-linear evaluation of a power system as it moves through state space. A system linearization occurs first to compute a multi-objective state space controller. For each contingency definition, many variations of the power system example are created and assigned to the particular contingency class. The powerflow variations and contingency controls are combined to run sets of time series analysis in which the Lyapunov function is tracked over three time steps. This data is utilized for a classification analysis which identifies and classifies the data by the contingency type. The goal is that whenever a new event occurs on the system, real time data can be fed into the trained tree to provide a control for application to increase system damping.<br>Ph. D.
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Sumsurooah, Sharmila. "Robust stability analysis of power electronic systems." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/37829/.
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Power electronics is the enabling technology that can put transportation on a more sustainable pathway. The key problem with power electronic (PE) systems is that they are prone to instability. Classical techniques are insufficient at assessing the stability of these systems, as they do not take into account the uncertain nature of physical systems. This thesis presents the structured singular value (SSV) method as an effective, reliable and robust stability analysis approach that justifiably incorporates uncertainties which are inherently present in physical systems. Although the SSV approach has numerous benefits, it has a few drawbacks that tend to make it hard to apply. Its theoretical framework remains complex. The practical approaches to applying the SSV method to PE systems seem lacking in the literature. The SSV approach is generally applied to linear system models while most systems are non-linear in nature. This thesis demonstrates the applicability of the SSV method to PE systems, by addressing these limitations. The work first brings deeper and clearer insights into key concepts of SSV theory. It demonstrates the significance and usefulness of the robust stability measure (SSV) in the space of multiple parametric uncertainties, through the concept of the hypercube. Secondly, it presents several practical approaches to applying the SSV method to PE systems. Finally, it develops a modelling methodology that converts a non-linear system to an equivalent linear model, suited for SSV analysis. The findings are supported by simulation and experimental results of the buck converter, permanent magnet machine drive, ideal constant power load and resistance-inductance-capacitance systems. This thesis provides the design engineer with some crucial theoretical and practical tools for applying the SSV approach to both linear and non-linear models of PE systems, while showing how to reap the full benefits of the method. It is the author's belief that the SSV method can be used as widely as classical methods, and to great effect.
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Anderson, Sharon Lee. "Reduced order power system models for transient stability studies." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-09052009-040743/.
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Hiskens, Ian A. "Energy functions, transient stability and voltage behaviour /." Online version, 1990. http://bibpurl.oclc.org/web/30417.
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Kunwar, Amit. "Stability aspects of wind power integration in power systems and microgrids." Thesis, Kunwar, Amit (2019) Stability aspects of wind power integration in power systems and microgrids. PhD thesis, Murdoch University, 2019. https://researchrepository.murdoch.edu.au/id/eprint/49890/.
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Wind farms can be located in remote and weak parts of power networks, due to the availability of wind energy. With integration of power from such wind farms, the power system’s stability might be affected especially at higher penetration levels. Instability issues resulting from such incorporations must be addressed to accommodate higher wind power penetration in the power networks. This thesis attempts to analyse the stability issues of power system with integration of variable speed wind turbine technology especially focusing on doubly fed induction generators. Additionally, a microgrid with different inertial and non-inertial sources is examined for enhancing design aspect of such microgrids from stability perspectives.
At different penetration levels of wind power, oscillatory modes are identified, and participation factors of the most associated state variables on such oscillatory modes are observed. Flexible ac transmission system based series and shunt devices are found effective in enhancing the small signal stability of such power networks for different wind power penetration levels. Besides, series devices are observed to contribute to an improvement in the transient behaviour of the power system. Similarly, high voltage dc link is also witnessed to positively influence low frequency oscillation damping. Furthermore, this thesis shows that higher voltage gain values of wind farms can contribute to an improvement in the small signal stability for increased wind power penetration. Another observation displays that a doubly fed induction based wind farm can contribute to improving the voltage stability of a distribution network in a steady state operating condition, as well as following disturbances. Based on the study on an isolated microgrid that has a combination of synchronous, converter-based distributed resources, and energy storage systems, it is observed that a suitable modification in such microgrid’s various components and parameters can positively influence its small signal stability.
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Areerak, Kongpan. "Modelling and stability analysis of aircraft power systems." Thesis, University of Nottingham, 2009. http://eprints.nottingham.ac.uk/12944/.
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The more-electric aircraft concept is a major trend in aircraft electrical power system engineering and results in an increase in electrical loads based on power electronic converters and motor drive systems. Unfortunately, power electronic driven loads often behave as constant power loads having the small-signal negative impedance that can significantly degrade the power system stability margin. Therefore, the stability issue of aircraft power systems is of great importance. The research of the thesis deals with the modelling and stability analysis of an aircraft power system. The aircraft power system architecture considered in the thesis is based on the More Open Electrical Technologies (MOET) aircraft power system with one generator as only a single generator can be connected to a system at any one time. The small-signal stability analysis is used with the system dynamic model derived from the dq modelling method under the assumption that the aircraft power system operating point does not change rapidly during normal operation mode. The linearization technique using the first order terms of a Taylor expansion is used so as to achieve a set of linear models around an equilibrium point for a small-signal stability study. The thesis presents the development of effective models capable of representing the electrical power system dynamic behaviour for stability studies. The proposed model can be used to predict the instability point for variations in operating points and/or system parameters. Agreement between the theoretical estimation, simulation, and experimental results for a simple system are achieved that ranges from acceptable to very good. Finally, the subsystem models described in the thesis can be interconnected in an algorithmic way that is representative of a more generalized aircraft power system model. The generalized model is also applied to a more complex and realistic aircraft power system with simulation validations for thorough investigations of aircraft power system stability. This model may be considered as a powerful and flexible stability analysis tool to analyse the complex multi-converter electrical power systems.
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Zhang, Xiaorui. "Voltage stability analysis and control in power systems." Thesis, University of Strathclyde, 2007. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=21656.
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Under the title of Voltage Stability Analysis and Control, three major subjects have been examined in this PhD project: the fundamental study of voltage stability, the on-line prediction method for voltage collapse, and secondary voltage control systems. The fundamental study was aimed to lay a theoretical foundation for the rest of research in this project. The on-line prediction method and secondary voltage control systems are particularly targeting on the "early prediction and prevention" strategy to tackle the rapid and "uncontrollable" nature of the voltage collapse phenomenon. The work on the fundamental study was presented in chapter 3 of this thesis. The basic characteristics of voltage collapse were examined, the theory concerning the voltage stability determining factors (VSDFs) was established. Based on this fundamental study, a knowledge based system for the on-line prediction of voltage collapse was proposed in chapter 4. The pattern recognition technique was used in this prediction system, and the design and development of such a system were intensively discussed in this chapter. As a well recognised prevention measure to voltage collapse, secondary voltage control systems were systematically investigated in chapter 5,6, and 7 of this thesis. Chapter 5 deals with the principle of secondary voltage control, and the design and analysis of such a system by classic and optimal control were presented in chapter 6 and 7 respectively. As a further study, improving voltage stability through generation dispatch was also briefly discussed at the end of this thesis. An algorithm aimed at this purpose was proposed to determine the generation participation pattern upon system load increase. All the studies in this project were simulated on the standard IEEE test power systems, some of the study results have been published in the different international conferences or academic forums.
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Zhang, Richard Yi. "Robust stability analysis for large-scale power systems." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/108846.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2017.<br>This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.<br>Cataloged from student-submitted PDF version of thesis.<br>Includes bibliographical references (pages 145-154).<br>Innovations in electric power systems, such as renewable energy, demand-side participation, and electric vehicles, are all expected to increase variability and uncertainty, making stability verification more challenging. This thesis extends the technique of robust stability analysis to large-scale electric power systems under uncertainty. In the first part of this thesis, we examine the use of the technique to solve real problems faced by grid operators. We present two case studies: small-signal stability for distributed renewables on the IEEE 118-bus test system, and large-signal stability for a microgrid system. In each case study, we show that robust stability analysis can be used to compute stability margins for entire collections of uncertain scenarios. In the second part of this thesis, we develop scalable algorithms to solve robust stability analysis problems on large-scale power systems. We use preconditioned iterative methods to solve the Newton direction computation in the interior-point method, in order to avoid the O(n6) time complexity associated with a dense-matrix approach. The per-iteration costs of the iterative methods are reduced to O(n3) through a hierarchical block-diagonal-plus-low-rank structure in the data matrices. We provide evidence that the methods converge to an [epsilon]-accurate solution in O(1=[square root of ] [epsilon]) iterations, and characterize two broad classes of problems for which the enhanced convergence is guaranteed.<br>by Richard Yi Zhang.<br>Ph. D.
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Huynh, Phuong. "Stability analysis of large-scale power electronics systems." Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/40205.
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A new methodology is proposed to investigate the large-signal stability of interconnected power electronics systems. The approach consists of decoupling the system into a source subsystem and a load subsystem, and stability of the entire system can be analyzed based on investigating the feedback loop formed by the interconnected source/load system. The proposed methodology requires two stages: (1) since the source and the load are unknown nonlinear subsystems, system identification, which consists of isolating each subsystem into a series combination of a linear part and a nonlinear part, must be performed, and (2) stability analysis of the interconnected system is conducted thereafter based on a developed stability criterion suitable for the nonlinear interconnected-block-structure model. Applicability of the methodology is verified through stability analysis of PWM converters and a typical power electronics system.<br>Ph. D.
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Amy, John Victor. "Composite system stability methods applied to advanced shipboard electric power systems." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/10945/23576.
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CIVINS<br>Large increases in the complexity of shipboard electric loads as well as development of electric drive, integrated electric drive and pulsed power systems make manifest the present and future importance of naval electric power systems. The most crucial attribute of these systems is their ability to fulfill their function in the presence of "large-signal" perturbations. Fundamental differences between shipboard and commercial electric power systems make all but the most general nonlinear, "large-signal" stability analyses inappropriate for the design and assessment of naval electric power systems. The tightly coupled and compact nature of shipboard systems are best accommodated by composite system stability analyses. Composite system methods, based upon Lyapunov's direct method, require that each component's stability be represented by a Lyapunov function. A new Lyapunov function which is based upon coenergy is developed for 3-phase synchronous machines. This use of coenergy is generalizable to all electromechanical energy conversion devices. The coenergy-based Lyapunov function is implemented as a "stability organ" which generates waveforms at information teirninals of a "device object" in the object oriented simulation environment of WAVESIM. Single generator simulation results are used to acquire a measure of the "over sufficiency" of the coenergy-based Lyapunov function. Some means of combining the components' Lyapunov functions is necessary with composite system stability criterions. To provide the largest stability region in a Lyapunov function convective derivative space, thereby reducing "over sufficiency", a "timevariant weighted-sum" composite system criterion is developed. This criterion is implemented as a "stability demon" "device object" within the WAVESIM environment. The "stability demon" is tested through RLC circuit simulations and a two-generator simulation. The output of the "stability demon" is suitable for use within an overall system stabilising controller.
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Farsangi, Malihe Maghfouri. "Robust control of flexible AC transmission systems for damping power system oscillations." Thesis, Brunel University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269400.
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Dale, L. A. "Real-time modelling of multimachine power systems." Thesis, University of Bath, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374598.
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Zhou, Ning. "Subspace methods of system identification applied to power systems." Laramie, Wyo. : University of Wyoming, 2005. http://proquest.umi.com/pqdweb?did=1095432761&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.
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Cheung, Siu-pan. "Direct transient stability margin assessment of power system with excitation control and SVC control /." Hong Kong : University of Hong Kong, 1996. http://sunzi.lib.hku.hk/hkuto/record.jsp?B1753706X.
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Cvetkovic, Milos. "Power-Electronics-Enabled Transient Stabilization of Power Systems." Research Showcase @ CMU, 2013. http://repository.cmu.edu/dissertations/344.
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Transient stability of electric energy grids is defined as the ability of the power system to remain in synchronism during large disturbances. If the grid is not equipped with controllers capable of transiently stabilizing system dynamics, large disturbances could cause protection to trigger disconnecting the equipment and leading further to cascading system-wide blackouts. Today’s practice of tuning controllers generally does not guarantee a transiently stable response because it does not use a model for representing system-wide dynamic interactions. To overcome this problem, in this thesis we propose a new systems modeling and control design for provable transient stabilization of power systems against a given set of disturbances. Of particular interest are fast power-electronically-controlled Flexible Alternating Current Transmission System (FACTS) devices which have become a new major option for achieving transient stabilization. The first major contribution of this thesis is a framework for modeling of general interconnected power systems for very fast transient stabilization using FACTS devices. We recognize that a dynamic model for transient stabilization of power systems has to capture fast electromagnetic dynamics of the transmission grid and FACTS, in addition to the commonly-modeled generator dynamics. To meet this need, a nonlinear dynamic model of general interconnected electric power systems is derived using time-varying phasors associated with states of all dynamic components. The second major contribution of this thesis is a two-level approach to modeling and control which exploits the unique network structure and enables preserving only relevant dynamics in the nonlinear system model. This approach is fundamentally based on separating: a) internal dynamics model for ensuring stable local response of components; b) system-level model in terms of interaction variables for ensuring stability of the system when the components are interconnected. The two levels can be controlled separately which minimizes the need for communication between controllers. Both distributed and cooperative ectropy-based controllers are proposed to control the interaction-level of system dynamics. Proof of concept simulations are presented to illustrate and compare the promising performance of the derived controllers. Some of the most advanced FACTS industry installations are modeled and further generalized using our approach.
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Zhang, Yi. "Adaptive remedial action schemes for transient instability." Online access for everyone, 2007. http://www.dissertations.wsu.edu/Dissertations/Fall2007/y_zhang_112707.pdf.
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Wang, Min. "Pattern recognition methodology for network-based diagnostics of power quality problems /." Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/6099.
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Parsi-Feraidoonian, Raiomand. "Application of catastrophe theory to transient stability analysis of multimachine power systems." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/29723.
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Transient stability analysis is an important part of power planning and operation. For large power systems, such analysis is very time consuming and expensive. Therefore, an online
transient stability assessment will be required as these large power systems are operated close to their maximum limits. In this thesis swallowtail catastrophe is used to determine the transient stability regions. The bifurcation set represents the transient stability region in terms of power system transient parameters bounded by the transient stability limits. The system modelling is generalized in such, that the analysis could handle either one or any number of critical machines. This generalized model is then tested on a three-machine as well as a seven-machine system. The results of the stability analysis done with the generalized method is compared with the time solution and the results were satisfactory. The transient stability regions determined are valid for any changes in loading conditions and fault location. This method is a good candidate for on-line assessment of transient stability of power systems.<br>Applied Science, Faculty of<br>Electrical and Computer Engineering, Department of<br>Graduate
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Jiriwibhakorn, Somchat. "Transient stability assessment of power systems using neural networks." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249489.
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Hong, Mingguo. "Controllability and diagnosis in electric power systems /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/6088.
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曾坤明 and Kwan-ming Tsang. "Decoupling and stabilizing control of multi-machine power systems withstatic VAr compensators." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1993. http://hub.hku.hk/bib/B31211008.
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Teeuwsen, Simon P. "Oscillatory stability assessment of power systems using computational intelligence." [S.l. : s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=974964263.
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WENG, CHIYUAN. "Transient Stability Analysis of Power Systems with Energy Storage." Case Western Reserve University School of Graduate Studies / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=case1348453228.
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Ebrahimpour, Mohammad Reza. "An analytical study of the power flow equations with applications to systems with multiple close solutions." Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/15746.
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Bremner, Jonathan James. "Complex torque coefficient analysis of multi-device power systems." Thesis, University of Glasgow, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362955.
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張小彬 and Siu-pan Cheung. "Direct transient stability margin assessment of power system with excitation control and SVC control." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1996. http://hub.hku.hk/bib/B31212979.
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Khan, Atif Zaman. "Eigenvalue sensitivites and their applications to power system voltage stability." Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/13911.
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Zhang, Yang. "Design of wide-area damping control systems for power system low-frequency inter-area oscillations." Online access for everyone, 2007. http://www.dissertations.wsu.edu/Dissertations/Fall2007/y_zhang_112007.pdf.
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Kang, Rizhong. "Preventive and Corrective Control of Voltage Stability in Electric Power Systems." Thesis, The University of Sydney, 2018. http://hdl.handle.net/2123/19789.
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This thesis proposes a novel approach aiming to counteract short term voltage fluctuations and transient instability by employing centralized emergency demand response. The objectives in this optimization model include a proposed short-term voltage stability index, inversed transient stability margin and system operation cost. Combined demand response actions of load shedding and load recovery are applied during the corrective period. To reduce computational complexity, load shedding bus candidates are selected based on trajectory sensitivity ranking with respect to the load shedding quantities. Then the optimization model is solved via multi-objective evolutionary algorithms (MOEAs). Compared with existing practices, this work not only coordinates between preventive control (PC) and corrective control (CC) actions, but also considers a proposed user disruption indicator to reflect power supply deviation from nominal demand during load shedding and load recovery periods. A comprehensive three-dimensional Pareto-optimal trade-off solution is computed for decision-making. The proposed method is verified by simulation results on the IEEE 39-bus system.
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Elkington, Katherine. "On the Use of Wind Power for Transient Stability Enhancement of Power Systems." Thesis, KTH, Elektriska energisystem, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-118931.
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This report deals with the impact of doubly fed induction generators on the stability of a power system. The impact was quantified by means of detailed numerical simulations. The report contains a full description of the simulation, and details of the small signal analysis performed to analyse the system. Before the simulation results are presented, a foundation is laid, explaining the theory required to understand the models used and the calculations performed in the simulation. The derivation of a model of a doubly fed induction generator is presented, along with a description of the model of a synchronous generator. These are used in the simulation and analysis of a multi-machine power system, consisting of both of these types of generators. An explanation of how dynamic simulations of power systems can be performed is also put forward. This is useful, not only for understanding the simulation performed for this report, but as a guide to performing simulations of this type. This is true also for a description of linearisation and small signal analysis contained in this report. The software package MATLAB is used to perform the simulations, and the small signal analysis. Since the method described in this report is very general, it can be used to perform similar power system simulations for other power systems, and with other software. Numerical simulations reveal that the addition of doubly fed generators, such as those in wind parks, to a power system improves the response of the system after small disturbances, but can worsen it after larger disturbances.
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Parsons, Antony Cozart. "Automatic location of transient power quality disturbances /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
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Ghasemi, Hassan. "On-line Monitoring and Oscillatory Stability Margin Prediction in Power Systems Based on System Identification." Thesis, University of Waterloo, 2006. http://hdl.handle.net/10012/834.
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Poorly damped electromechanical modes detection in a power system and corresponding stability margins prediction are very important in power system planning and operation, and can provide significant help to power system operators with preventing stability problems. <br /><br /> Stochastic subspace identification is proposed in this thesis as a technique to extract the critical mode(s) from the measured ambient noise without requiring artificial disturbances (e. g. a line outage), allowing these critical modes to be used as an on-line index, which is referred here to as System Identification Stability Indices (SISI) to predict the closest oscillatory instability. The SISI is not only independent of system models and truly representative of the actual system, but also computationally efficient. In addition, readily available signals in a power system and several identification methods are categorized, and merits and pitfalls of each one are addressed in this work. <br /><br /> The damping torque of linearized models of power systems is studied in this thesis as another possible on-line security index. This index is estimated by means of proper system identification techniques applied to both power system transient response and ambient noise. The damping torque index is shown to address some of drawbacks of the SISI. <br /><br /> This thesis also demonstrates the connection between the second order statistical properties, including confidence intervals, of the estimated electromechanical modes and the variance of model parameters. These analyses show that Monte-Carlo type of experiments or simulations can be avoided, hence resulting in a significant reduction in the number of samples. <br /><br /> In these types of studies, the models available in simulation packages are extremely important due to their unquestionable impact on modal analysis results. Hence, in this thesis, the validity of generator subtransient model and a typical STATCOM transient stability (TS) model are also investigated by means of system identification, illustrating that under certain conditions the STATCOM TS model can yield results that are too optimistic, which can lead to errors in power system planning and operation. <br /><br /> In addition to several small test systems used throughout this thesis, the feasibility of the proposed indices are tested on a realistic system with 14,000 buses, demonstrating their usefulness in practice.
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Kasis, Andreas. "Distributed schemes for stability and optimality in power networks." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/270819.
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The generation, transmission and distribution of electricity underpins modern technology and constitutes a necessary element for our development and economic functionality. In the recent years, as a result of environmental concerns and technological advances, private and public investment have been steadily turning towards renewable sources of energy, resulting in a growing penetration of those in the power network. This poses additional challenges in the control of power networks, since renewable generation is in general intermittent, and a large penetration may cause frequent deviations between generation and demand, which can harm power quality and even cause blackouts. Load side participation in the power grid is considered by many a means to counterbalance intermittent generation, due to its ability to provide fast response at urgencies. Industrial loads as well as household appliances, may respond to frequency deviations by adjusting their demand in order to support the network. This is backed by the development of relevant sensing and computation technologies. The increasing numbers of local renewable sources of generation along the introduction of controllable loads dramatically increases the number of active elements in the power network, making traditionally implemented, centralised control dicult and costly. This demonstrates the need for the employment of highly distributed schemes in the control of generation and demand. Such schemes need to ensure the smooth and stable operation of the network. Furthermore, an issue of fairness among controllable loads needs to be considered, such that it is ensured that all loads share the burden to support the network evenly and with minimum disruption. We study the dynamic behaviour of power networks within the primary and secondary frequency control timeframes. Using tools from non-linear control and optimisation, we present methods to design distributed control schemes for generation and demand that guarantee stability and fairness in power allocation. Our analysis provides relaxed stability conditions in comparison with current literature and allows the inclusion of practically relevant classes of generation and demand dynamics that have not been considered within this setting, such as of higher order dynamics. Furthermore, fairness in the power allocation between loads is guaranteed by ensuring that the equilibria of the system are solutions to appropriately constructed optimisation problems. It is evident that a synchronising variable is required for optimality to be achieved and frequency is used as such in primary control schemes whereas for secondary frequency control a dierent synchronising variable is adopted. For the latter case, the requirements of the synchronising feedback scheme have been relaxed with the use of an appropriate observer, showing that stability and optimality guarantees are retained. The problem of secondary frequency regulation where ancillary services are provided from switching loads is also considered. Such loads switch on and off when some prescribed frequency threshold is reached in order to support the power network at urgencies. We show that the presence of switching loads does not compromise the stability of the power network and reduces the frequency overshoot, potentially saving the network from collapsing. Furthermore, we explain that when the on and o switching frequencies are equivalent, then arbitrarily fast switching phenomena might occur, something undesirable in practical implementations. As a solution to this problem, hysteresis schemes where the switch on and off frequencies differ are proposed and stability guarantees are provided within this setting.
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Knazkins, Valerijs. "Stability of power systems with large amounts of distributed generation." Doctoral thesis, KTH, Electrical Systems, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-46.
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<p>This four-part dissertation is essentially concerned with some theoretical aspects of the stability studies of power systems with large penetration levels of distributed generation. In particular, in Parts I and II the main emphasis is placed upon the transient rotor angle and voltage stability. The remaining two parts are devoted to some system-theoretic and practical aspects of identification and modeling of aggregate power system loads, design of auxiliary robust control, and a general qualitative discussion on the impact that distributed generation has on the power systems. </p><p>One of the central themes of this dissertation is the development of analytical tools for studying the dynamic properties of power systems with asynchronous generators. It appears that the use of traditional tools for nonlinear system analysis is problematic, which diverted the focus of this thesis to new analytical tools such as, for example, the Extended Invariance Principle. In the framework of the Extended Invariance Principle, new extended Lyapunov functions are developed for the investigation of transient stability of power systems with both synchronous and asynchronous generators. In most voltage stability studies, one of the most common hypotheses is the deterministic nature of the power systems, which might be inadequate in power systems with large fractions of intrinsically intermittent generation, such as, for instance, wind farms. To explicitly account for the presence of intermittent (uncertain) generation and/or stochastic consumption, this thesis presents a new method for voltage stability analysis which makes an extensive use of interval arithmetics. </p><p>It is a commonly recognized fact that power system load modeling has a major impact on the dynamic behavior of the power system. To properly represent the loads in system analysis and simulations, adequate load models are needed. In many cases, one of the most reliable ways to obtain such models is to apply a system identification method. This dissertation presents new load identification methodologies which are based on the minimization of a certain prediction error. </p><p>In some cases, DG can provide ancillary services by operating in a load following mode. In such a case, it is important to ensure that the distributed generator is able to accurately follow the load variations in the presence of disturbances. To enhance the load following capabilities of a solid oxide fuel plant, this thesis suggests the use of robust control. This dissertation is concluded by a general discussion on the possible impacts that large amounts of DG might have on the operation, control, and stability of electric power systems.</p>
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Zadehkhost, Sajjad. "Efficient algorithms to expedite transient stability analysis of power systems." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/52816.
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With rapid increase in complexity of modern power systems, there is a strong need for better computational tools to ensure the reliable operation of electrical grids. These tools need to be accurate, computationally efficient, and capable of using advanced measurement devices. In this context, transient stability assessment (TSA) is an important study that determines system’s dynamic security margins following a major disturbance. The TSA consists of a set of differential-algebraic equations (DAEs), which are typically solved using time-domain simulation (TDS) approach. While being very accurate, the TDS requires significant computational resources when applied to practical power systems. This problem becomes more significant in transient stability monitoring (TSM), wherein the computational performance of the TDS is typically the bottleneck. This research is to investigate available challenges in the TSM applications and develop new algorithms to help realizing a practical monitoring tool for transient stability studies. The thesis focuses on three research thrusts: i) dynamic reduction of power system to reduce problem size; ii) advanced computation approaches to expedite the TDS method; iii) integration of PMU measurements into the TSM. Initially, a new adaptive aggregation algorithm for dynamic reduction is proposed, wherein parameters of generators and structure of transmission network are considered to aggregate coherent generators and create a reduced-order system. Also, a new criterion is defined to monitor validity of the constructed reduced system. It is shown that the proposed technique is more accurate than traditional aggregation methods. To expedite the TDS approach, this thesis presents two new integration techniques, which are called Multi-Decomposition Approach (MDA) and Successive Linearization and Integration Technique (SLIT). In these methods, the nonlinear DAEs are decomposed into a series of linear subsystems, which participate in approximating actual solution. It is demonstrated that sequential and parallel versions of the MDA and SLIT are faster than state-of-the-art integration techniques. Finally, a dynamic state estimator based on Extended Kalman Filter is developed to convert the PMU measurements into a set of state variables suitable for transient stability studies. Computer studies show that the proposed framework provides accurate results in highly disturbed power systems with fairly low PMU sampling rates.<br>Applied Science, Faculty of<br>Electrical and Computer Engineering, Department of<br>Graduate
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Mihirig, Ali Mohamed. "Transient stability analysis of multimachine power systems by catastrophe theory." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/29022.
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Transient stability analysis is an important part of power system planning and operation. For large power systems, such analysis is very demanding in computation time. On-line transient stability assessment will be necessary for secure and reliable operation of power systems in the near future because systems are operated close to their maximum limits.
In the last two decades, a vast amount of research work has been done in the area of fast transient stability assessment by direct methods. The major difficulties associated with direct methods are the limitations in the power system model, determination of transient stability regions and adaptation to changes in operating conditions. In this thesis catastrophe theory is used to determine the transient stability regions. Taylor series expansion is used to find the energy balance equation in terms of clearing time and system transient parameters. The energy function is then put in the form of a catastrophe manifold from which the bifurcation set is extracted. The bifurcation set represents the transient stability region in terms of the power system transient parameters bounded by the transient stability limits. The transient stability regions determined are valid for any changes in loading conditions and fault location. The transient stability problem is dealt with in the two dimensions of transient stability limits and critical clearing times. Transient stability limits are given by the bifurcation set and the critical clearing times are calculated from the catastrophe manifold equation. The method achieves a breakthrough in the modelling problem because the effects of exciter response, flux decay and systems damping can all be included in the transient stability analysis. Numerical examples of one-machine infinite-bus and multi-machine power systems show very good agreement with the time solution in the practical range of first swing stability analysis. The method presented fulfills all requirements for on-line assessment of transient stability of power systems.<br>Applied Science, Faculty of<br>Electrical and Computer Engineering, Department of<br>Graduate
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Al, Marhoon Hussain Hassan. "A Practical Method for Power Systems Transient Stability and Security." ScholarWorks@UNO, 2011. http://scholarworks.uno.edu/td/114.
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Stability analysis methods may be categorized by two major stability analysis methods: small-signal stability and transient stability analyses. Transient stability methods are further categorized into two major categories: numerical methods based on numerical integration, and direct methods. The purpose of this thesis is to study and investigate transient stability analysis using a combination of step-by-step and direct methods using Equal Area Criterion. The proposed method is extended for transient stability analysis of multi machine power systems. The proposed method calculates the potential and kinetic energies for all machines in a power system and then compares the largest group of kinetic energies to the smallest groups of potential energies. A decision based on the comparison can be made to determine stability of the power system. The proposed method is used to simulate the IEEE 39 Bus system to verify its effectiveness by comparison to the results obtained by pure numerical methods.
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O'Rourke, Colm J. "Decentralized power systems : reference-frame theory and stability region generation." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/127082.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, May, 2020<br>Cataloged from the official PDF of thesis.<br>Includes bibliographical references (pages 87-91).<br>Electricity provides the foundation for many of today's technological advances. The desire for energy security, a reduction in carbon dioxide emissions and a diversification of resources are all motivations for changes in how electricity is generated and transmitted. Recent alternatives to traditional centralized power-plants include technologies that are decentralized and intermittent, such as solar photovoltaic and wind power. This trend poses considerable challenges in the hardware making up these systems, the software that control and monitor power networks and their mathematical modelling. This thesis presents a set of contributions that address some of the aforementioned challenges. Firstly, we examine the fundamental theories used in modelling and controlling power systems. We expand previous work on reference-frame theory, by providing an alternative interpretation and derivation of the commonly used Park and Clarke transformations. We present a geometric interpretation that has applications in power quality. Secondly, we introduce a framework for producing regions of stability for power systems using conditional generative adversarial neural networks. This provides transmission and distribution operators with an accurate set of control options even as the system changes significantly.<br>by Colm J. O'Rourke.<br>Ph. D.<br>Ph.D. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science
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Praprost, Kenneth Lee. "Power system stability and security methods with applications to restorative state operation." Case Western Reserve University School of Graduate Studies / OhioLINK, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=case1060190618.
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Schooley, David C. "Unit commitment and system reliability in electric utility systems with independent wind and solar generation." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/12917.
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Sayler, Kent Alexander Halpin S. Mark. "Predicting generator coupling using power system impedance matrices." Auburn, Ala., 2006. http://repo.lib.auburn.edu/2006%20Spring/master's/SAYLER_KENT_33.pdf.
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Wu, Qiang. "Dynamics and coordinated control of voltage behavior in power systems." Thesis, The University of Sydney, 2000. https://hdl.handle.net/2123/27766.
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This thesis presents results on the dynamics and coordinated control of voltage behavior
in power systems.
The first part of the thesis is on dynamic modeling, with emphasis on tap-changing
transformers and load dynamics. For both, highly simplified models are used in voltage
stability analysis, despite the complex nature of the devices involved, i.e. tap changing
operation and aggregate load. The operating conditions, under which the stability results
based on these simplified models are reliable need to be clarified. A study is carried
out on the influence of diiferent discrete and continuous tap models on voltage stability
properties, particularly when combined with load dynamics. It has been found that
small disturbance analysis, especially if based on the common continuous tap model with
fixed time constant, is often an unreliable indicator of system stability. Some important
differences in system responses with continuous and discrete tap models are highlighted
along with the conditions under which they occur.
Limit cycles are shown to characterize the system responses with discrete tap models. The
limit cycles originate from the deadband nonlinearity embedded in the discrete tap operation
and tap-load interactions. Describing functions for the nonlinearity of the discrete
tap operation are derived and used to predict the existence of limit cycles. Furthermore,
the feasibility of avoiding the limit cycles through adjusting deadband size is investigated.
It has been shown that whether or not increasing deadband can always eliminate
the existing limit cycle depends on the associated load dynamics.
Following this, attention is given to load dynamics modeling. The focus is on use of
generic dynamic load models. A simulation study is given on system behavior with generic
dynamic loads as compared with the detailed physically based load models which they ap—
proximate. Several simple and a more complicated load structures are considered, which
include lower voltage tap changers, induction motors, thermostatically controlled heating
and static load. It has been shown, for simple load structures, generic dynamic load models,
if the parameters are properly identified, provide fairly accurate prediction of system
stability behavior in all cases except the one with high percentage of induction motors.
On the other hand, for a load structure with diverse compositions, generic dynamic load
models have practically useful accuracy for representing the load. This suggests that ap—
plying generic dynamic load models will be practically useful in reducing the complexity
of system modeling and give reliable stability analysis results.
The second part of the thesis is devoted to coordinated voltage control. A general frame
work for coordinating optimally a diverse set of control actions is established. The benefit
of control coordination is illustrated through a case study on coordination of capacitor
switching and tap locking. By careful coordination of these controls, voltage collapse can
be arrested with less overall control effort and less impact on the voltage profile than by
either acting along.
An analytical framework for coordinated voltage control based on coordination of dissimilar
control actions is then presented. A 4-stage optimal control scheme is proposed along
with detailed formulations. In the first three stages, a security constrained steady—state
approach is used to define the optimal control direction for providing stability and adequate
security margin. An algorithm based on differential dynamic programming based
is then used to optimally schedule controls with different response time and dynamics.
Finally, the dynamic sensitivity-based method is employed to refine the obtained control
sequence; in terms of finding the optimal switching times for the control actions identified
in earlier stages.
In the final study of the thesis, application is made of the stability analysis and coordinated
control techniques to a substantial physical power system, namely the New South Wales
power grid. The algorithm and techniques proposed in previous chapters is tested in a
more practical situation.