Neste trabalho, as restrições de estabilidade transitória são incorporadas ao problema de Fluxo de Potência Ótimo (FPO) por meio da aproximação de equações diferenciais do problema de estabilidade por um conjunto de equações algébricas provenientes de procedimentos de integração numérica. Uma contribuição original desta dissertação é a proposição de um procedimento de otimização multi-passos que minimiza problemas de convergência e acelera o processo computacional. O procedimento de otimização proposto foi testado com sucesso num sistema pequeno de 3 geradores, tendo as potências geradas como variáveis de controle. / In this work, transient stability constraints are incorporated into the Optimal Power Flow (OPF) problem by approximating differential equations constraints by a set of equivalent algebraic equations originated from numerical integration procedures. A contribution of this dissertation is the proposal of a multi-step optimization procedure, which minimizes convergence problems and speeds up computation. The proposed optimization procedure was successfully tested on a small 3-machine power system, having the generated powers as control variables.

Recent widespread blackouts have indicated the need for more efficient and accurate power system monitoring, control and protection tools. Power system state estimation, which is the major tool that is used nowadays for providing the real-time model of the system, has significant biases resulting mainly from the complexity and geographic spread and separation of an electric power system. Synchrophasor technology is a promising technology that has numerous advantages compared to conventional metering devices. PMUs provide synchronized measurements, where synchronization is achieved via a GPS clock which provides the synchronizing signal with accuracy of 1 μsec. As a result, the computed phasors have a common reference (UTC time) and can be used in local computations, thus distributing the state estimation process. The first part of the work presents a PMU enabled dynamic state estimator (DSE) that can capture with high fidelity the dynamics of the system and extract in real time the dynamic model of the system. The described DSE is performed in a decentralized way, on the substation level based on local measurements which are globally valid. The substation based DSE uses data from relays, PMUs, meters, FDRs etc in the substation only, thus avoiding all issues associated with transmission of data and associated time latencies. This approach enables very fast DSE update rate which can go up to more than 60 executions per second. The distributed state estimation architecture that synchrophasor technology enables, along with the fast sampling rate and the accuracy of the measurements that PMUs provide, enable the computation of the real-time dynamic model of the system and the development of numerous power system applications for more efficient control and protection of the system. In the second part of the work, a transient stability monitoring scheme is presented that utilizes the information given by the dynamic state estimation and enables real-time monitoring of the transient swings of the system and characterizes the stability of the system in real time. In particular, the real-time dynamic model of the system, as given by the DSE, is utilized to evaluate the system's energy function based on Lyapunov's direct method and extract stability properties from the energy function. The two major components of the scheme are a) the calculation of the center of oscillations of the system and b) the derivation of an equivalent, reduced sized model which is used for the calculation of the potential and kinetic energy of the system based on which the stability of the system is determined. Finally, as an application of the transient stability monitoring scheme, an energy based out-of-step protection scheme is proposed. The energy of the generator is continuously monitored and if it exceeds a predefined threshold then instability is asserted and a trip signal can be sent to the generator. The major advantage of the scheme is that the out-of-step condition is predicted before its occurrence and therefore relays can act much faster than today's technology. The scheme is compared to presently available state of the art out-of-step protection schemes in order to verify its superiority.

<p>Utilization of power electronics based controllable systems (or devices) in transmission systems has opened new opportunities for the power industry to optimize utilization of the existing transmission systems, and at the same time to keep high system reliability and security.</p><p>As a member of these controllable systems, Voltage Source Converters-based High Voltage direct current (VSC-HVdc) systems have the ability to rapidly control the transmitted active power, and also to independently exchange reactive power with transmissions systems. Therefore, VSC-HVdcs with a suitable control scheme can offer an alternative means to enhance transient stability, to improve power oscillations damping, and to provide voltage support. An interesting application of this system is the analysis of a power system when a VSC-HVdc is connected in parallel with ac transmission lines.</p><p>This thesis presents the derivation of control strategies to damp power oscillations, to enhance the transient stability and to provide voltage support for a VSC-HVdc. The thesis also formulates a multichoice control strategy and its application when the VSC-HVdc is connected in a synchronous system.</p><p>The control strategy for enhancing transient stability is based on the theory of Control Lyapunov Function. The control strategy for increasing the damping is based on Linear Analysis. A very effective well known way to increase damping in the system is modulating the active power through the HVdc. However, besides the control of active power, the thesis explores an alternative way to mitigate power oscillations by controlling the reactive power. This condition might be very useful when the dc link in the VSC-HVdc system is out of service, but the converter stations are in operating conditions.</p><p>A simple model of VSC-HVdc is considered in order to test the control strategy. The model represents the VSC-HVdc as an element in the power system that provides adequate interaction with other systems elements. The model is intended for analysis of power flows and electromechanical transients. It is then sufficient to consider the power frequency components of voltages and currents represented by phasors that vary with time during transients. The model is valid for symmetrical conditions, i.e. positive sequence phasors are used for the representation of the electrical state.</p>

The purpose of this research is to develop a method of making system equivalents for the Real Time Digital Simulator (RTDS), which should enhance its capability of simulating large power systems. The proposed equivalent combines a Frequency Dependent Network Equivalent (FDNE) for the high frequency electromagnetic transients and a Transient Stability Analysis (TSA) type simulation block for the electromechanical transients. The frequency dependent characteristic for FDNE is obtained by curve-fitting frequency domain admittance characteristics using the Vector Fitting method. An approach for approximating the frequency dependent characteristic of large power networks from readily available typical power-flow data is also introduced. A new scheme of incorporating TSA solution in RTDS is proposed. This report shows how the TSA algorithm can be adapted to a real time platform. The validity of this method is confirmed with examples, including the study of a multi in-feed HVDC system based network.

The purpose of this research is to develop a method of making system equivalents for the Real Time Digital Simulator (RTDS), which should enhance its capability of simulating large power systems. The proposed equivalent combines a Frequency Dependent Network Equivalent (FDNE) for the high frequency electromagnetic transients and a Transient Stability Analysis (TSA) type simulation block for the electromechanical transients. The frequency dependent characteristic for FDNE is obtained by curve-fitting frequency domain admittance characteristics using the Vector Fitting method. An approach for approximating the frequency dependent characteristic of large power networks from readily available typical power-flow data is also introduced. A new scheme of incorporating TSA solution in RTDS is proposed. This report shows how the TSA algorithm can be adapted to a real time platform. The validity of this method is confirmed with examples, including the study of a multi in-feed HVDC system based network.

Orientador: Laurence Duarte Colvara / Banca: Carlos Roberto Minussi / Banca: Wagner Peron Ferreira / Resumo: Este trabalho apresenta um estudo sobre a relação entre os principais tipos de bifurcações que ocorrem em sistemas elétricos de potência e em quais ocasiões elas podem ocorrer em máquinas síncronas com ou sem RAT (Regulador Automático de Tensão). Para explorar tais fenômenos, primeiramente o sistema é modelado, sendo utilizado para o caso MBI (Máquina - Barramento In nito) o modelo um eixo e, então, a matriz de estado é calculada para a análise dos autovalores. Para os sistemas multimáquinas estudados, são incluídos dois enrolamentos amortecedores nos eixos d ¡ q. São então apresentados os métodos de análise de estabilidade transitória convencionais, amplamente utilizados, conhecidos como método Tradicional e Método Direto. As condições para a ocorrência de bifurcações são analisadas utilizando os coe - cientes linearizados do modelo de He ron-Phillips para o caso MBI, onde é mostrado que se espera perder a estabilidade para o sistema com regulador automático de tensão através de uma bifurcação de Hopf e para o caso sem RAT através de uma bifurcação Sela-Nó. Por m, é analisado o ciclo-limite para o caso de uma máquina - barramento in nito e para sistemas multimáquinas através do modelo não-linear. A região de estabilidade é analisada no plano de fase, sendo mostrada a necessidade de incluir a variação de uxo no enrolamento de campo para uma análise correta da estabilidade. É também mostrado que este ciclo-limite pode reduzir a fronteira de estabilidade calculada pelo método convencional. / Abstract: The aim of this study is the relation among main types of bifurcations that occur in electrical power systems and the circumstances they can happen with the synchronous machines considered with or without AVR (Automatic Voltage Regulator). To explore such phenomena, the system is rst modeled with the synchronous machines described by the one axis model for the MIB (Machine - In nite Bus) case , and so the state matrix is computed for the analysis of its eigenvalues. For multimachine systems case two windings dampers are included in d-q axes. The conditions for the occurrence of bifurcations are analyzed using the coe cients of the He ron-Phillips model for MIB case, where it is shown that one expects the system with automatic voltage regulator lose synchronism through a Hopf bifurcation and for the case without RAT through a Saddle- Node Bifurcation. Finally, the nonlinear model is accounted for in order to consider the limit-cycle for the case of one machine - in nite bus case as well as for multimachine system. Since internal voltage a ects the boundary of the stability region it must be considered. Then the phase portrait does not su ce and the trajectories must to be observed in a sub space de ned with the internal voltage. It is also shown that this limit-cycle can reduce the boundary of stability calculated by means of the direct method. / Mestre

abstract: Electric power system security assessment is one of the most important requirements for operational and resource planning of the bulk power system ensuring safe operation of the power system for all credible contingencies. This deterministic approach usually provides a conservative criterion and can result in expensive bulk system expansion plans or conservative operating limits. Furthermore, with increased penetration of converter-based renewable generation in the electric grid, the dynamics of the grid are changing. In addition, the variability and intermittency associated with the renewable energy sources introduce uncertainty in the electricity grid. Since security margins have direct economic impact on the utilities; more clarity is required regarding the basis on which security decisions are made. The main objective of this work is to provide an approach for risk-based security assessment (RBSA) to define dynamic reliability standards in future electricity grids. RBSA provides a measure of the security of the power system that combines both the likelihood and the consequence of an event. A novel approach to estimate the impact of transient stability is presented by modeling several important protection systems within the transient stability analysis. A robust operational metric to quantify the impact of transient instability event is proposed that incorporates the effort required to stabilize any transiently unstable event. The effect of converter-interfaced renewable energy injection on system reliability is investigated us-ing RBSA. A robust RBSA diagnostics tool is developed which provides an interactive user interface where the RBSA results and contingency ranking reports can be explored and compared based on specific user inputs without executing time domain simulations or risk calculations, hence providing a fast and robust approach for handling large time domain simulation and risk assessment data. The results show that RBSA can be used effectively in system planning to select security limits. Comparison of RBSA with deterministic methods show that RBSA not only provides less conservative results, it also illustrates the bases on which such security decisions are made. RBSA helps in identifying critical aspects of system reliability that is not possible using the deterministic reliability techniques. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2017

Made available in DSpace on 2014-06-11T19:22:35Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-02-22Bitstream added on 2014-06-13T18:49:40Z : No. of bitstreams: 1 pereira_mbc_me_ilha.pdf: 1170771 bytes, checksum: f8ba8678a1d9af0316e036187c7f36d7 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este trabalho tem por objetivo contribuir para o desenvolvimento de técnicas de Educação em Engenharia apresentando uma ferramenta de apoio ao Ensino/Aprendizagem de Sistemas Elétricos de Potência na forma de um software de interface amigável e baixo custo. O software desenvolvido em linguagem C++ segue os padrões de programação orientada a objetos e oferece ao usuário a resolução de fluxos de potência e simulações de casos de contingências transitórias com possibilidade de interatividade, apresentando resultados em ambiente gráfico. Desenvolvido para aplicação na área de Dinâmica e Estabilidade de Sistemas de Potência, suporta sistemas-exemplos clássicos do IEEE e também disponibiliza ao usuário ferramentas para personalização de arquivos de dados de entrada, tornando-se flexível e de fácil acesso aos casos já inseridos no sistema. O usuário também pode criar novos sistemas de acordo com suas necessidades. Os resultados são exibidos em forma numérica e também através de gráficos tridimensionais e animação, possibilitando fácil visualização de resultados, entendimento de fenômenos e análise de influências sobre o desempenho. / This work presents a contribution to the development of Engineering Education techniques by means of a Teaching/Learning support tool for Electrical Power System studies resulting in a friendly low cost interface software. It was developed in C++ language and follows the pattern of object oriented programming, offering to the user the resolution of load flow and digital simulations of transient stability with the possibility of interactivity, showing the results in a graphic environment. It was developed for use in applications of Static and Transient Power Systems Stability and it has enclosed classic sample-systems of IEEE and others and also allows the user to customize input data files. Then the tool is flexible and enables easy access to cases formerly inserted in the system. The user also can create new systems according to his needs. The machines rotors movement can be seen in a graphic animation, allowing easy visualization of events, phenomena comprehension and analysis of influences about the performance.

Orientador: Laurence Duarte Colvara / Banca: Sergio Azevedo de Oliveira / Banca: Silvia Galvão de Souza Cervantes / Resumo: Este trabalho tem por objetivo contribuir para o desenvolvimento de técnicas de Educação em Engenharia apresentando uma ferramenta de apoio ao Ensino/Aprendizagem de Sistemas Elétricos de Potência na forma de um software de interface amigável e baixo custo. O software desenvolvido em linguagem C++ segue os padrões de programação orientada a objetos e oferece ao usuário a resolução de fluxos de potência e simulações de casos de contingências transitórias com possibilidade de interatividade, apresentando resultados em ambiente gráfico. Desenvolvido para aplicação na área de Dinâmica e Estabilidade de Sistemas de Potência, suporta sistemas-exemplos clássicos do IEEE e também disponibiliza ao usuário ferramentas para personalização de arquivos de dados de entrada, tornando-se flexível e de fácil acesso aos casos já inseridos no sistema. O usuário também pode criar novos sistemas de acordo com suas necessidades. Os resultados são exibidos em forma numérica e também através de gráficos tridimensionais e animação, possibilitando fácil visualização de resultados, entendimento de fenômenos e análise de influências sobre o desempenho. / Abstract: This work presents a contribution to the development of Engineering Education techniques by means of a Teaching/Learning support tool for Electrical Power System studies resulting in a friendly low cost interface software. It was developed in C++ language and follows the pattern of object oriented programming, offering to the user the resolution of load flow and digital simulations of transient stability with the possibility of interactivity, showing the results in a graphic environment. It was developed for use in applications of Static and Transient Power Systems Stability and it has enclosed classic sample-systems of IEEE and others and also allows the user to customize input data files. Then the tool is flexible and enables easy access to cases formerly inserted in the system. The user also can create new systems according to his needs. The machines rotors movement can be seen in a graphic animation, allowing easy visualization of events, phenomena comprehension and analysis of influences about the performance. / Mestre

Made available in DSpace on 2014-12-17T14:55:57Z (GMT). No. of bitstreams: 1 ClovisBMO.pdf: 4499915 bytes, checksum: b3ed589a5cb7e5f7a1b113d606f615e2 (MD5) Previous issue date: 2006-02-20 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / This work presents a description of models development at DigSILENT PowerFactoryTM program for the transient stability study in power systems with wind turbine. The main goal is to make available means to use a dynamic simulation program in power systems, widely published, and utilize it as a tool that helps in programs results evaluations used for this intent. The process of simulations and analyses results starts after the models setting description phase. The results obtained by the DigSILENT PowerFactoryTM and ATP, program chosen to the validation also international recognized, are compared during this phase. The main tools and guide lines of PowerFactoryTM program use are presented here, directing these elements to the solution of the approached problem. For the simulation it is used a real system which it will be connected a wind farm. Two different technologies of wind turbines were implemented: doubly-fed induction generator with frequency converter, connecting the rotor to the stator and to the grid, and synchronous wind generator with frequency converter, interconnecting the generator to the grid. Besides presenting the basic conceptions of dynamic simulation, it is described the implemented control strategies and models of turbine and converters. The stability of the wind turbine interconnected to grid is analyzed in many operational conditions, resultant of diverse kinds of disturbances / Este trabalho apresenta uma descri??o do desenvolvimento de modelos no programa DigSILENT PowerFactoryTM voltados ao estudo de estabilidade transit?ria em sistemas de pot?ncia com aerogerador. O objetivo ? disponibilizar meios para se utilizar um programa de simula??o din?mica em sistemas de pot?ncia, amplamente divulgado, e utiliz?-lo como uma ferramenta que auxilie na avalia??o dos resultados de programas usados para este fim. Ap?s a fase de descri??o da montagem dos modelos inicia-se o processo de simula??o e an?lise dos resultados. ? durante esta fase que s?o comparados os resultados do DigSILENT PowerFactoryTM com os resultados obtidos com o ATP, programa escolhido para avalia??o, tamb?m com reconhecimento internacional. S?o apresentadas as principais ferramentas e diretrizes do uso do programa PowerFactoryTM, direcionando tais elementos ? solu??o do problema formulado. Para simula??o, utiliza-se uma rede real, na qual ser? introduzido um parque e?lico. Dois tipos de tecnologias de gera??o e?lica foram implementadas: aerogerador de indu??o duplamente excitado com conversor de freq??ncia, conectando o rotor ao estator e ? rede, e aerogerador s?ncrono com conversor de freq??ncia, interligando o gerador ? rede. Al?m de apresentar os conceitos b?sicos de simula??o din?mica, descrevem-se as estrat?gias de controle implementadas e os modelos de turbinas e conversores. A estabilidade do aerogerador interligado ? rede ? avaliada em diversas condi??es operacionais, resultante de variados tipos de perturba??es