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The robustness of the stability property of multivariable feedback control systems with respect to model uncertainty is studied and discussed. By introducing a topological notion of arcwise connectivity, existing and new robust stability tests are combined and unified under a common framework. The new switching-type robust stability test is easy to apply, and does not require the nominal and perturbed plants to share the same number of closed right half-plane poles, or zeros, or both. It also highlights the importance of both the sensitivity matrix and the complementary sensitivity matrix in determining the robust stability of a feedback system. More specifically, it is shown that at those frequencies where there is a possibility of an uncertain pole crossing the jw-axis, robust stability is "maximized" by minimizing the maximum singular value of the sensitivity matrix. At frequencies where there is a likelihood of uncertain zeros crossing the imaginary axis, it is then desirable to minimize the maximum singular value of the complementary sensitivity matrix. A robustness optimization problem is posed as a non-square H^∞-optimization problem. All solutions to the optimization problem are derived, and parameterized by the solutions to an "equivalent" two-parameter interpolation problem. Motivated by improvements in disturbance rejection and robust stability, additional optimization objectives are introduced to arrive at the 'best' solution.

Thesis (M.S.)--Rochester Institute of Technology, 1994. / Typescript. Includes bibliographical references.

In this work we introduce a novel queueing model with two classes of users in which, instead of accessing a resource, users wait in the system to match with a candidate from the other class. The users are selective and the matchings occur probabilistically. This new model is useful for analysing the traffic in web portals that match people who provide a service with people who demand the same service, e.g. employment portals, matrimonial and dating sites and rental portals. We first provide a Markov chain model for these systems and derive the probability distribution of the number of matches up to some finite time given the number of arrivals. We then prove that if no control mechanism is employed these systems are unstable for any set of parameters. We suggest four different classes of control policies to assure stability and conduct analysis on performance measures under the control policies. Contrary to the intuition that the rejection rate should decrease as the users become more likely to be matched, we show that for certain control policies the rejection rate is insensitive to the matching probability. Even more surprisingly, we show that for reasonable policies the rejection rate may be an increasing function of the matching probability. We also prove insensitivity results related to the average queue lengths and waiting times. Further, to gain more insight into the behaviour of probabilistic matching systems, we propose approximation methods based on fluid and diffusion limits using different scalings. We analyse the basic properties of these approximations and show that some performance measures are insensitive to the matching probability agreeing with the results found by the exact analysis. Finally we study the optimal control and revenue management for the systems with the objective of profit maximization. We formulate mathematical models for both unobservable and observable systems. For an unobservable system we suggest a deterministic optimal control, while for an observable system we develop an optimal myopic state dependent pricing.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Norman August Lehtomaki. / Ph.D.

Voltage unbalance performance of a power line depends on a few parameters that are not necessarily constant at any given instance. The random nature of a power system raises questions around the ability of a system planner to allocate equitable share of the power quality parameters, like voltage unbalance, at design stage. Even a more interesting question is whether applying current methods will guarantee that emissions will be under the set limits. The presence of single or dual phase feeders on such a line will result in a more dynamic voltage unbalance. The first part of this research is a study on deterministic method of voltage unbalance allocation presented by the IEC. The IEC 61000-13-3 report is a comprehensive guideline and the best place to start when looking to develop an emissions standard for voltage unbalance. This dissertation presents a method that can be used to set planning levels for unbalance emission at various voltage levels in order to avoid high voltage unbalance at the end user. The method depends on the agreed power of the customer, the power of the unbalanced load, and the system characteristics. The method works well for short feeders with roughly the same negative sequence impedance and equal short circuit levels. In South Africa, however, there are radial feeders that span over 100km. Hence on such a feeder, there can be ratios of 1:10 between sending end and the last customer on the line. Preliminary research revealed that IEC 61000-6-3, a report on allocation of harmonics, has a method applicable to long feeders. This method was investigated extensively and applied to voltage unbalance allocation. At the core of the method is the assumption that feeders have an even distribution of load. To illustrate the application of this method an example is given. The second part of the study explores a stochastic method of voltage unbalance allocation. In this study the possibility of random connection is considered. A Monte Carlo study is presented. The impact of various parameters are analysed and the findings reveal that phase allocation has the most influence on emission. The results show that the method of random connection of loads can be applied in special conditions only i.e. were sizes of loads do not differ greatly and the number of required connections are low. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.

Made available in DSpace on 2014-06-11T19:22:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-05-25Bitstream added on 2014-06-13T20:08:28Z : No. of bitstreams: 1 martins_rvf_me_ilha.pdf: 1143165 bytes, checksum: 34607cda52dfc8bc20e888b8601f3e4b (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / PROPG - Programa de Pós-Graduação / Este trabalho dedica-se ao estudo da contribuição do SVC (Static Var Compensator) na estabilidade transitória em sistema multimáquinas. Coeficientes de sensibilidade nomeados fator de efeito e coeficiente de eficácia auxiliam na compreensão da atuação do SVC na admitância de transferência entre máquinas, que por sua vez exercem grande influência na capacidade de sincronização do sistema multimáquinas. Estuda-se a dinâmica da compensação do SVC neste trabalho, considerando dois controladores, sendo controle de tensão e controle estabilizador suplementar, este com sinal de entrada remoto das variações das velocidades angulares. Tais controladores, por meio da variação da susceptância do SVC, proporcionam influência na energia potencial do sistema, com reflexos diretos nas cordilheiras energéticas em torno de um ponto de operação, alterando o relevo energético proporcionando maiores condições de estabilidade comprovadas pela elevação do tempo crítico de eliminação de uma falta / This work is dedicated to the study of the SVC (Static Var Compensator) contribution on the transient stability in multimachine power system. Coefficients of sensibility named effect factor and coefficient of efficiency help on the comprehension the influence of the SVC in the transference admittance between machines, which, on the other hand, have great influence on the synchronization capacity of the multimachine system. It is studied the dynamic of the SVC compensation in this work, considering two controllers, which are voltage control and supplementary stabilizer control, this one with remote signal input being the angular speeds variations. Such controllers, through the variation of the SVC susceptance, provide influence on the system potential energy, with direct reflections on the energy ridges around an operation point, altering the energy relief providing major conditions of stability proven by the elevation of the critical time of elimination of a fault

Orientador: Laurence Duarte Colvara / Banca: Percival Bueno de Araujo / Banca: George Lauro Ribeiro de Brito / Resumo: Este trabalho dedica-se ao estudo da contribuição do SVC (Static Var Compensator) na estabilidade transitória em sistema multimáquinas. Coeficientes de sensibilidade nomeados fator de efeito e coeficiente de eficácia auxiliam na compreensão da atuação do SVC na admitância de transferência entre máquinas, que por sua vez exercem grande influência na capacidade de sincronização do sistema multimáquinas. Estuda-se a dinâmica da compensação do SVC neste trabalho, considerando dois controladores, sendo controle de tensão e controle estabilizador suplementar, este com sinal de entrada remoto das variações das velocidades angulares. Tais controladores, por meio da variação da susceptância do SVC, proporcionam influência na energia potencial do sistema, com reflexos diretos nas cordilheiras energéticas em torno de um ponto de operação, alterando o relevo energético proporcionando maiores condições de estabilidade comprovadas pela elevação do tempo crítico de eliminação de uma falta / Abstract: This work is dedicated to the study of the SVC (Static Var Compensator) contribution on the transient stability in multimachine power system. Coefficients of sensibility named effect factor and coefficient of efficiency help on the comprehension the influence of the SVC in the transference admittance between machines, which, on the other hand, have great influence on the synchronization capacity of the multimachine system. It is studied the dynamic of the SVC compensation in this work, considering two controllers, which are voltage control and supplementary stabilizer control, this one with remote signal input being the angular speeds variations. Such controllers, through the variation of the SVC susceptance, provide influence on the system potential energy, with direct reflections on the energy ridges around an operation point, altering the energy relief providing major conditions of stability proven by the elevation of the critical time of elimination of a fault / Mestre

Orientador: Carlos Alberto de Castro Junior / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-12T09:57:48Z (GMT). No. of bitstreams: 1 Fujisawa_CassioHideki_M.pdf: 844179 bytes, checksum: 599c2d5e9fde47013351265d74d7b02a (MD5) Previous issue date: 2008 / Resumo:Neste trabalho de pesquisa propõe-se uma ferramenta flexível para o Cálculo da margem de segurança de redes de distribuição de energia elétrica com relação à estabilidade e de tensão. Esta margem de segurança está relacionada à distância (em termos da carga)entre o ponto de operação atual e o ponto de operação correspondente à máxima carga admissível. Esta ferramenta utiliza um fluxo de carga pelo método de Newton modificado e se presta também avaliar certos impactos da inserção da geração distribuída sobre a operação da rede. A metodologia proposta mostra-se adequada inclusive em ambientes sujeitos a severas restrições de tempo computacional, como a operação em tempo real de sistemas elétricos de potência. / Abstract: A flexible tool for computing the voltage stability security margin of distributions systems is proposed in this research work. This security margin corresponds to the distance (in load parameter space) from the Current operating point to the maximum loading point. This tool uses a modified Newton's load flow method and it is also useful for evaluating Certain impacts of the insertion of distributed generation on the system operation. The proposed methodology has shown to be suited for environment subjected to severe computation time constraints, such as power systems real time operation. / Mestrado / Energia Eletrica / Mestre em Engenharia Elétrica

According to the proposed definition and classification of power system stability addressed by IEEE and CIGRE Task Force, voltage stability refers to the stability of maintaining the steady voltage magnitudes at all buses in a power system when the system is subjected to a disturbance from a given operating condition (OC). Cascading outage due to voltage collapse is a probable consequence during insecure voltage situations. In this regard, fast responding and reliable voltage security assessment (VSA) is effective and indispensable for system to survive in conceivable contingencies. This paper aims at establishing an online systematic framework for voltage security assessment with high-speed data streams from synchrophasors and phasor data concentrators (PDCs). Periodically updated decision trees (DTs) have been applied in different subjects of security assessments in power systems. However, with a training data set of operating conditions that grows rapidly, re-training and restructuring a decision tree becomes a time-consuming process. Hoeffding-tree-based method constructs a learner that is capable of memory management to process streaming data without retaining the complete data set for training purposes in real-time and guarantees the accuracy of learner. The proposed approach of voltage security assessment based on Very Fast Decision Tree (VFDT) system is tested and evaluated by the IEEE 118-bus standard system. / Master of Science