Thesis (M.S.)--Mississippi State University. Department of Electrical and Computer Engineering. / Title from title screen. Includes bibliographical references.

Thesis (M.S.) -- Mississippi State University. Department of Electrical and Computer Engineering. / Title from title screen. Includes bibliographical references.

abstract: The standard optimal power flow (OPF) problem is an economic dispatch (ED) problem combined with transmission constraints, which are based on a static topology. However, topology control (TC) has been proposed in the past as a corrective mechanism to relieve overloads and voltage violations. Even though the benefits of TC are presented by several research works in the past, the computational complexity associated with TC has been a major deterrent to its implementation. The proposed work develops heuristics for TC and investigates its potential to improve the computational time for TC for various applications. The objective is to develop computationally light methods to harness the flexibility of the grid to derive maximum benefits to the system in terms of reliability. One of the goals of this research is to develop a tool that will be capable of providing TC actions in a minimal time-frame, which can be readily adopted by the industry for real-time corrective applications. A DC based heuristic, i.e., a greedy algorithm, is developed and applied to improve the computational time for the TC problem while still maintaining the ability to find quality solutions. In the greedy algorithm, an expression is derived, which indicates the impact on the objective for a marginal change in the state of a transmission line. This expression is used to generate a priority list with potential candidate lines for switching, which may provide huge improvements to the system. The advantage of this method is that it is a fast heuristic as compared to using mixed integer programming (MIP) approach. Alternatively, AC based heuristics are developed for TC problem and tested on actual data from PJM, ERCOT and TVA. AC based N-1 contingency analysis is performed to identify the contingencies that cause network violations. Simple proximity based heuristics are developed and the fast decoupled power flow is solved iteratively to identify the top five TC actions, which provide reduction in violations. Time domain simulations are performed to ensure that the TC actions do not cause system instability. Simulation results show significant reductions in violations in the system by the application of the TC heuristics. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2016

Made available in DSpace on 2014-06-11T19:22:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-11-19Bitstream added on 2014-06-13T18:49:32Z : No. of bitstreams: 1 menezes_mm_me_ilha.pdf: 769292 bytes, checksum: 4b80be15a6104228fa9612312498644f (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este trabalho apresenta estudos referentes à estabilidade a pequenas perturbações do SEP, considerando a atuação de FACTS para o amortecimento das oscilações eletromecânicas de baixa frequência. São abordados os dispositivos FACTS TCSC (Thyristor Controlled Series Capacitor) e o SSSC (Static Synchronous Series Compensator). É realizada a representação e modelagem dos dispositivos FACTS no SEP inserindo no Modelo Sensibilidade de Potência. Para melhorar o desempenho do SEP no que se refere à estabilidade a pequenas perturbações, controladores suplementares são propostos para aumentar o desempenho dos dispositivos TCSC e SSSC, introduzindo o amortecimento necessário ao SEP. Adicionam-se os controladores suplementares POD no modelo modificado para os dispositivos TCSC e SSSC para verificar sua atuação. Para encontrar a melhor localização para instalação dos dispositivos é usado a teoria dos resíduos. Esta mesma teoria é usada também para o ajuste dos parâmetros dos controlares juntamente com outro ajuste feito através de Redes Neurais Artificiais (RNA), que é proposto como alternativa de comparação ao método dos resíduos. Simulações são efetuadas em um sistema teste simétrico para se verificar resultados e a eficácia do controlador POD (parâmetros ajustados pela RNA proposta), acoplados aos dispositivos FACTS, na manutenção da estabilidade a pequenas perturbações do SEP. Palavras-chave: Controladores POD. Estabilidade de sistema de potência. Redes neurais artificiais. TCSC e SSSC / This work presents studies referred to short term Electric Power System (EPS) perturbations, considering the actuation of FACTS devices for low frequency electromechanical oscillation damping. The devices considered are: FACTS TCSC (Thyristor Controlled Series Capacitor) and the SSSC (Static Synchronous Series Compensator). It is representation and modeling FACTS devices in the EPS inserting in the Power Sensitivity Model. To improve the performance of the EPS considering the short term perturbations, additional controllers are proposed to increase the performance of the TCSC and SSSC devices, introducing the necessary damping to the EPS. The additional POD controller is added to the modified model for TCSC and SSSC devices to verify the acting. The residual theory is used to find the best location to install the devices. The same theory is used to adjust the parameters of the controllers and an adjustment with Artificial Neural Networks (ANN) is proposed as an alternative to the residual method. Simulations are effectuated for a symmetric test system to verify the efficiency of the POD controller (parameters adjusted by the ANN proposed), coupled with the FACTS devices, to maintain the stability considering the short term perturbations

Orientador: Walmir de Freitas Filho / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-16T21:04:55Z (GMT). No. of bitstreams: 1 Ricciardi_TiagoRodarte_M.pdf: 3291776 bytes, checksum: c647c3c5eaa394835294087b10e89863 (MD5) Previous issue date: 2010 / Resumo: O uso de geradores conectados via inversores em redes de distribuição de energia elétrica tem aumentado consideravelmente nos últimos anos em razão dos avanços obtidos nas tecnologias de células a combustível e fotovoltaicas bem como de microturbinas e turbinas eólicas. Nesse contexto, a utilização de sistemas de proteção antiilhamento no ponto de conexão do gerador com a rede elétrica é uma das exigências previstas nos principais guias técnicos empregados pelas concessionárias. Ilhamento ocorre quando uma parte da rede de distribuição torna-se eletricamente isolada da fonte de energia principal (subestação), mas continua a ser energizada por geradores distribuídos conectados no subsistema isolado. No caso particular dos geradores conectados via inversores, os principais dispositivos utilizados comercialmente para fornecer proteção antiilhamento são baseados no conceito de realimentação positiva, cuja idéia básica é empregar um dos parâmetros que definem a tensão terminal do gerador como sinal de realimentação positiva no seu sistema controle. Caso o gerador esteja conectado ao sistema de distribuição, a realimentação positiva não consegue, a priori, desestabilizar o gerador. Por outro lado, caso o gerador torne-se ilhado, a realimentação positiva fará com que o gerador se torne instável e, por conseguinte, a situação de ilhamento pode ser rapidamente detectada por relés de sub/sobre tensão e/ou sub/sob freqüência. Visto que tal esquema de proteção esforça-se para desestabilizar o gerador independentemente da ocorrência ou não de ilhamentos, é fundamental desenvolver ferramentas para analisar a estabilidade de redes com múltiplos geradores equipados com proteção antiilhamento via realimentação positiva. O objetivo desta dissertação de mestrado foi desenvolver uma série de modelos linearizados no espaço de estados para representar os principais dispositivos de proteção antiilhamento existentes comercialmente a fim de investigar a estabilidade frente a pequenas perturbações de sistemas de distribuição de energia elétrica com múltiplos geradores conectados via inversores utilizando-se análise modal / Abstract: The usage of inverter-based generators connected directly to electric Power distribution systems has considerably increased in recent years due to the technological advances of fuel and photovoltaic cells as well as microturbines and wind turbines. In this context, the usage of anti-islanding protection devices at the interconnection point is required by the main technical guides utilized by the utilities. Islanding occurs when a portion of the distribution system becomes electrically isolated from the remainder of the power system, yet continues to be energized by distributed generators. In the case of inverter-based generators, the main devices commercially employed to supply anti-islanding protection are based on the positive feedback concept. These methods use the deviations of voltage frequency and/or magnitude from normal values as positive feedback signals into the control system to influence the operation of inverterbased distributed generators. If the generator is connected to a strong utility system, in priori, the destabilizing force of the positive feedback has a negligible impact and the generator can operate without difficulties. On the other hand, when the generator is islanded, the positive feedback can destabilize the generator easily. Such distinctively different generator behaviors facilitate the detection of islanding conditions by using under/over voltage and frequency relays. Since the positive feedback scheme is a destabilizing force, the impact of this scheme on the stability of system with multiples inverter-based generators is of concern. If the positive feedback gain is too high, the generator may become unstable even if it is connected to the main supply system. Thus, the objective of this master thesis is to develop several small-signal models to investigate the stability of distribution network with multiple inverter-based generators with positive feedback anti-islanding protection by using modal analysis / Mestrado / Energia Eletrica / Mestre em Engenharia Elétrica

Orientador : Vivaldo Fernando da Costa / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-04T02:42:32Z (GMT). No. of bitstreams: 1 Domingues_AdrianaFavaro_D.pdf: 789245 bytes, checksum: 9ca2b124a01cd871aa7f4bbb4c63c57a (MD5) Previous issue date: 2005 / Resumo: Este trabalho aborda o problema das oscilações eletromecânicas de baixa freqüência de modo interárea em sistemas de energia elétrica através de duas metodologias: primeiramente, através do método convencional da análise modal linear e, posteriormente, através da aplicação do método da forma normal dos campos vetoriais como ferramenta para viabilizar o acréscimo dos termos não lineares de segunda ordem resultantes da expansão em série de Taylor. Neste caso, o método da forma normal é aplicado a um Modelo de Sensibilidade de Potência com representação de segunda ordem, para investigar os efeitos das interações não lineares entre os modos naturais de oscilação de sistemas de energia elétrica. São consideradas, em ambas as análises, a inclusão de dispositivos FACTS e da modelagem dinâmica das cargas. As simulações são realizadas para um sistema simétrico de duas áreas e para o Sistema Equivalente Sul-Sudeste Brasileiro. A metodologia de análise proposta mostra-se bastante satisfatória como alternativa à simulação não linear no domínio do tempo e à análise modal convencional / Abstract: In this work, the analysis of power systems inter-area mode oscillations is performed by the application of two different methodologies: first, the linear modal analysis, and then the analysis including second order nonlinear terms from a Taylor series expansion, with the application of the method of normal forms of vector fields. In this case, the method of normal forms is applied to a Power Sensitivity Model including second order nonlinear terms, in order to investigate the effects of nonlinear interactions between system modes. Both methodologies consider the inclusion of FACTS devices and dynamic load model. Simulations are performed for a symmetric two-area test power system and for the Equivalent South-Southeast Brazilian system. The results obtained show that the methodology proposed is very effective as an alternative to linear modal analysis and timedomain simulation in the performance of inter-area mode oscillations analysis / Doutorado / Energia Eletrica / Doutor em Engenharia Elétrica

Orientador: Vivaldo Fernando da Costa / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-14T11:14:17Z (GMT). No. of bitstreams: 1 Paccini_RodrigodeOliveira_M.pdf: 1988341 bytes, checksum: 7be3a801c003202ec884c8313b60ac5f (MD5) Previous issue date: 2009 / Resumo: Quando um sistema interligado de corrente alternada sofre variações de carga, sua freqüência pode exibir um comportamento oscilatório. Se este mesmo sistema possuir um elo de corrente contínua em paralelo com as linhas de intercâmbio, esse efeito poderá ser atenuado devido à atuação do controlador de corrente do elo. Esta tese apresenta um estudo que avalia a eficiência de um elo de CC para o amortecimento de oscilações de freqüência de intercâmbio sob condições de pequenas perturbações, operando o sistema com Controle Automático de Geração (CAG). Um modelo de injeção de potência utilizado para representar o elo CC é implementado no Modelo de Sensibilidade de Potência (MSP). Uma das vantagens desse modelo é permitir o desacoplamento da rede em duas partes distintas: o balanço ativo e o balanço reativo, em que as duas podem ser tratadas juntas ou separadamente. Com a escolha desse modelo, tornou-se possível implementar toda a rede no formato de diagrama de blocos. Além disso, as barras de carga do sistema são acessíveis através do diagrama de blocos, o que torna possível variar também a característica da carga. Através dessa representação, tornou-se viável a inserção do elo de CC no diagrama de blocos, pois o mesmo foi modelado como uma injeção de potência nas barras terminais nos balanços ativo e reativo, fechando um novo balanço de potência. As análises no domínio do tempo foram realizadas no programa Matlab Simulink®. Também utilizando este software, um controlador de amortecimento de oscilações de potência (POD-Power Oscillation Damping Controller) foi projetado para a modulação da potência do elo de CC. Os resultados obtidos mostram que o elo de CC possui um grande potencial para a manutenção do amortecimento de oscilações de freqüência de modo inter-área, quando equipados com controladores POD. / Abstract: When an interconnected alternate-current power system suffers variations of loads, its frequency can exhibit an oscillatory behavior. If this system possesses a direct-current link in parallel with the inter-tie lines, this effect could be decreased, due to the link current controller action. This work presents a study that evaluates the efficiency of DC link for the damping of interarea frequency oscillations under small disturbances, operating the system with automatic generation control (AGC). A DC power injection model is implemented in the Power Sensitivity Model (PSM). One of the advantages of this model is to allow the detach of the network in two distinct parts: the active and reactive balances, where the two can be dealt together or separately. With the choice of this model, it's possible to implement the complete network in the block diagram format. Moreover, the network load bus are accessible through the block diagram, which this are possible to vary the load characteristic. Through this representation, the insertion of DC link in the block diagram became viable, therefore it was modeled as a power injection in the terminals bus in the active and reactive balances, closing a new power balance. The time domain analysis is carried out the software Matlab Simulink®. Also using this software, a POD controller (Power Oscillation Damping Controller) was designed for the DC power modulation. The results show that DC link comprises a great potential for the maintenance of frequency oscillations damping in interarea mode, when coupled to POD controllers. / Mestrado / Energia Eletrica / Mestre em Engenharia Elétrica

Les nouvelles politiques adoptées par les autorités nationales ont encouragé pendant les dernières années l'intégration à grande échelle des systèmes d'énergie renouvelable (RES). L'intégration à grande échelle des RES aura inévitablement des conséquences sur le réseau de transport d'électricité tel qu'il est conçu aujourd'hui, car le transport de l'électricité massif sur de longues distances pourrait amener les réseaux de transport à fonctionner près de leurs limites, réduisant ainsi leurs marges de sécurité. Des systèmes de transport d’électricité plus complexes seront donc nécessaires.Dans ce scénario, les systèmes de transmission à Courant Continu Haute Tension (HVDC) constituent la solution la plus intéressante pour le renforcement et l'amélioration des réseaux à Courant Alternatif (AC) existants, non seulement en utilisant des configurations point à point, mais aussi dans des configurations multi-terminales. L'introduction des systèmes HVDC aboutira à terme à un réseau électrique hybride haute tension AC/DC, qui doit être analysé comme un système unique afin de mieux comprendre les interactions entre le réseau AC et le réseau DC.Cette thèse porte sur l'analyse de la stabilité transitoire des systèmes de transmission électrique hybrides AC/DC. Plus particulièrement, deux questions ont été abordées: Quel est l'impact d'un défaut du réseau DC sur la stabilité transitoire du réseau AC? Comment est-il possible de se servir des systèmes de transmission DC en tant qu'actionneurs afin d'améliorer la stabilité transitoire AC ?Dans la première partie de ce travail, les modèles mathématiques du réseau hybride AC/DC sont décrits ainsi que les outils nécessaires à l'analyse du système en tenant compte de sa nature non linéaire. Ensuite, une analyse approfondie de la stabilité transitoire du réseau électrique dans le cas particulier d'un court-circuit dans le réseau DC et l'exécution des stratégies de protection correspondantes sont effectuées. En complément, des indicateurs de stabilité et des outils pour dimensionner les futurs réseaux de la MTDC afin de respecter les contraintes des stratégies de protection existantes sont proposés.La deuxième partie de la thèse porte sur les propositions de commande pour la modulation des références de puissance des systèmes de transmission HVDC dans le but d'améliorer la stabilité transitoire du système AC connecté à ce réseau DC. Tout d'abord, nous axons notre étude sur le contrôle non linéaire des liaisons HVDC point à point dans des liaisons hybrides AC/DC. La compensation rapide des perturbations de puissance, l'injection de puissance d'amortissement et l'injection de puissance de synchronisation sont identifiées comme des mécanismes par lesquels les systèmes HVDC peuvent améliorer les marges de stabilité des réseaux AC.Enfin, une stratégie de contrôle pour l'amélioration de la stabilité transitoire par injection de puissance active dans par un réseau MTDC est proposée. Grâce à la communication entre les stations, la commande décentralisée proposée injecte la puissance d'amortissement et de synchronisation entre chaque paire de convertisseurs en utilisant uniquement des mesures au niveau des convertisseurs. L'implémentation proposée permet d'utiliser au maximum la capacité disponible des convertisseurs en gérant les limites de puissance d'une manière décentralisée. / The new policy frameworks adopted by national authorities has encouraged the large scale-integration of Renewable Energy Systems (RES) into bulk power systems. The large-scale integration of RES will have consequences on the electricity transmission system as it is conceived today, since the transmission of bulk power over long distances could lead the existing transmission systems to work close to their limits, thus decreasing their dynamic security margins. Therefore more complex transmissions systems are needed.Under this scenario, HVDC transmission systems raise as the most attractive solution for the reinforcement and improvement of existing AC networks, not only using point-to-point configurations, but also in a Multi-Terminal configuration. The introduction of HVDC transmission systems will eventually result in a hybrid high voltage AC/DC power system, which requires to be analyzed as a unique system in order to understand the interactions between the AC network and the DC grid.This thesis addresses the transient stability analysis of hybrid AC/DC electric transmission systems. More in particular, two questions sought to be investigated: What is the impact of a DC contingency on AC transient stability? How can we take advantage of the of DC transmission systems as control inputs in order to enhance AC transient stability?In the first part of this work, the mathematical models of the hybrid AC/DC grid are described as well as the necessary tools for the analysis of the system taking into account its nonlinear nature. Then, a thorough analysis of transient stability of the power system in the particular case of a DC fault and the execution of the corresponding protection strategies is done. As a complement, stability indicators and tools for sizing future MTDC grids in order to respect the constraints of existing protection strategies are proposed.The second part of the thesis addresses the control proposals for the modulation of power references of the HVDC transmission systems with the purpose of transient stability enhancement of the surrounding AC system. Firstly, we focus our study in the nonlinear control of point-to-point HVDC links in hybrid corridors. Fast power compensation, injection of damping power and injection of synchronizing power are identified as the mechanisms through which HVDC systems can improve stability margins.Finally, a control strategy for transient stability enhancement via active power injections of an MTDC grid is proposed. Using communication between the stations, the proposed decentralized control injects damping and synchronizing power between each pair of converters using only measurements at the converters level. The proposed implementation allows to fully use the available headroom of the converters by dealing with power limits in a decentralized way.

In this report, the effect that a higher penetration ofrenewable energy sources has on electric power grid stability isevaluated. The report also compares different methods of stabilizingan unstable grid. The model used is a two-area four-machinesystem and the main objective is to stabilize the synchronousgenerators such that they revert back to synchronism afterbeing subjugated to a small signal disturbance. The stabilizationmethods consists of supplementary Power System Stabilizers(PSSs) complementing the exciter systems of the synchronousmachines, as well as two types of converter-based controllers inthe renewable energy source: Grid-Following (GFL) convertersand Grid-Forming (GFM) converters. The results show thata system with renewable energy sources is more sensitive todisturbances and has a larger rotor angle deviation from a steadystate when using only GFLs compared to the conventional gridwithout PSSs. It is also found that a conventional grid requiressupplementary PSSs to be stable. This is also the case for asystem with renewable energy controlled by GFL. The systemwith GFM controllers does however not need supplementary PSSto be stable. This leads to the conclusion that GFM is morepreferable than GFL to control a grid with a higher penetrationof renewable energy. / I denna rapport utvärderas hur en högre andel förnybara energikällor påverkar stabiliteten i elnät, och jämför också olika metoder för att stabilisera ett instabilt nät. Modellen som används var ett två-områdes-fyrmaskinsystem och huvudsyftet är att stabilisera synkrongeneratorerna så att de återgår till synkronism efter att ha utsatts för en liten småsignalsstörning. Stabiliseringsmetoderna består av kompletterande Power System Stabilizers (PSS:er) som kompletterade exciteringssystemen i synkronmaskinerna, samt två typer av omvandlarbaserade styrenheter i den förnybara energikällan: Grid-Following (GFL)-omvandlare och Grid-Forming (GFM)omvandlare. Resultaten visar att ett system med förnybara energikällor är mer känsligt för störningar och har en större rotorvinkelavvikelse från ett stationärt tillstånd när GFL-kontroller används jämfört med det konventionella nätet utan PSS:er. Det visar sig också att ett konventionellt nät kräver kompletterande PSS:er för att vara stabilt. Detta är också fallet för ett system med förnybar energi som enbart kontrolleras av GFL-omvandlare. Systemet med GFM-omvandlare behöver dock inte kompletterande PSS för att vara stabilt. Detta leder till slutsatsen att GFM är mer att föredra än GFL för att kontrollera ett nät med högre andel förnybar energi. / Kandidatexjobb i elektroteknik 2022, KTH, Stockholm

The study of nonlinear dynamical systems via the spectrum of the Koopman operator has emerged as a paradigm shift, from the Poincaré's geometric picture that centers the attention on the evolution of states, to the Koopman operator's picture that focuses on the evolution of observables. The Koopman operator-theoretic framework rests on the idea of lifting the states of a nonlinear dynamical system to a higher dimensional space; these lifted states are referred to as the Koopman eigenfunctions. To determine the Koopman eigenfunctions, one performs a nonlinear transformation of the states by relying on the so-called observables, that is, scalar-valued functions of the states. In other words, one executes a change of coordinates from the state space to another set of coordinates, which are denominated Koopman canonical coordinates. The variables defined on these intrinsic coordinates will evolve linearly in time, despite the underlying system being nonlinear. Since the Koopman operator is linear, it is natural to exploit its spectral properties. In fact, the theory surrounding the spectral properties of linear operators has well-known implications in electric power systems. Examples include small-signal stability analysis and direct methods for transient stability analysis based on the Lyapunov function. From the applications' standpoint, this framework based on the Koopman operator is attractive because it is capable of revealing linear and nonlinear modes by only applying well-established tools that have been developed for linear systems. With the challenges associated with the high-dimensionality and increasing uncertainties in the power systems models, researchers and practitioners are seeking alternative modeling approaches capable of incorporating information from measurements. This is fueled by an increasing amount of data made available by the wide-scale deployment of measuring devices such as phasor measurement units and smart meters. Along these lines, the Koopman operator theory is a promising framework for the integration of data analysis into our mathematical knowledge and is bringing an exciting perspective to the community. The present dissertation reports on the application of the Koopman operator for identification, estimation, and control of electric power systems. A dynamic state estimator based on the Koopman operator has been developed and compares favorably against model-based approaches, in particular for centralized dynamic state estimation. Also, a data-driven method to compute participation factors for nonlinear systems based on Koopman mode decomposition has been developed; it generalizes the original definition of participation factors under certain conditions. / PHD / Electric power systems are complex, large-scale, and given the bidirectional causality between economic growth and electricity consumption, they are constantly being expanded. In the U.S., some of the electric power grid facilities date back to the 1880s, and this aging system is operating at its capacity limits. In addition, the international pressure for sustainability is driving an unprecedented deployment of renewable energy sources into the grid. Unlike the case of other primary sources of electric energy such as coal and nuclear, the electricity generated from renewable energy sources is strongly influenced by the weather conditions, which are very challenging to forecast even for short periods of time. Within this context, the mathematical models that have aided engineers to design and operate electric power grids over the past decades are falling short when uncertainties are incorporated to the models of such high-dimensional systems. Consequently, researchers are investigating alternative data-driven approaches. This is not only motivated by the need to overcome the above challenges, but it is also fueled by the increasing amount of data produced by today’s powerful computational resources and experimental apparatus. In power systems, a massive amount of data will be available thanks to the deployment of measuring devices called phasor measurement units. Along these lines, the Koopman operator theory is a promising framework for the integration of data analysis into our mathematical knowledge, and is bringing an exciting perspective on the treatment of high-dimensional systems that lie in the forefront of science and technology. In the research work reported in this dissertation, the Koopman operator theory has been exploited to seek for solutions to some of the challenges that are threatening the safe, reliable, and efficient operation of electric power systems.