O crescimento da demanda por eletricidade tem promovido a diversificação da matriz energética em termos de fontes primárias, porte de geração e alocação dos geradores. Neste cenário, a inserção de geradores de pequeno porte nos sistemas de distribuição tem causado a descentralização da produção de energia elétrica e, no contexto nacional, o alto potencial para geração de eletricidade através de pequenas centrais hidrelétricas e usinas de cogeração tem dado destaque aos geradores síncronos distribuídos. Contudo, é necessário avaliar as implicações da presença dos geradores síncronos em sistemas de distribuição e avaliar se as metodologias já consagradas de análises, operação e normalização técnica estão adequadas. Dentre as principais peculiaridades dos sistemas de distribuição estão a proximidade dos geradores às cargas e a presença de eventos aleatórios de maior amplitude, tais como variações de carga que ocorrem natural e intermitentemente no sistema. Além disso, problemas relacionados a oscilações eletromecânica mal amortecidas podem agora ocorrer em níveis de distribuição e deve-se estabelecer um procedimento para identificação destes modos. Entretanto, o procedimento usual para o estudo de estabilidade a pequenas perturbações pode se tornar inviável, pois a construção do modelo completo é de extrema complexidade e os parâmetros dos elementos em níveis de distribuição são de difícil obtenção. Para reverter estes problemas citados, esta pesquisa oferece um procedimento alternativo para a obtenção dos modos de oscilação eletromecânica em sistemas de distribuição, sugerindo a estimação modal através de dados ambiente. / The electricity demand increase has promoted the energy matrix diversification in terms of primary sources, generation size and allocation of generators. In this scenario, the insertion of small sized generators in distribution systems has caused the power production decentralization and, in the national context, a high potential for generating electricity through small hydroelectric power plants and cogeneration plants has drawn attention to distributed synchronous generators. However, it is necessary to assess the implications of synchronous generators presence in distribution systems and evaluate if the current methodologies of analysis, operation and technical standards are appropriate to this context. Among the main distribution systems particularities, there are the proximity of generators to loads and more significant random perturbations conceptualized as load switching. In addition, problems related to lightly damped modes can occur in distribution and there is a need to establish a procedure for modal identification. However, the usual procedure for the small-signal stability analysis is not adequate to this problem, because the model construction is very complex and the parameters in distribution are very difficult to obtain. To face the challenges, this research provides an alternative procedure for obtaining electromechanical modes in distribution systems, suggesting modal estimation techniques that use measured ambient data.

Nesta tese de doutorado é proposta uma abordagem para estimar a velocidade angular de geradores síncronos conectados em um sistema elétrico de potência, a partir de sinais que podem ser facilmente mensurados, tais como a corrente e a tensão na barra do lado de alta tensão do transformador que conecta o gerador em análise ao restante do sistema. Uma vez que informações precisas sobre o comportamento dinâmico do sistema são de elevada importância para um controle efetivo do SEP, especialmente com o aumento da complexidade da rede, a abordagem proposta nesta tese fornece uma estimativa do sinal de velocidade que pode ser aplicada no estudo da estabilidade a pequenas perturbações para mitigar os problemas inerentes a presença das oscilações eletromecânicas mal amortecidas nos SEPs. A abordagem desenvolvida é composta por dois métodos sendo cada um deles aplicável dependendo das características do problema a ser resolvido e das informações disponíveis para tanto. No primeiro método, uma técnica de sensibilidade da trajetória é aplicada ao sinal de diferença entre a resposta obtida pelo modelo simulado e aquela fornecida por dados amostrados no sistema real emulado. A partir desse sinal de erro e das curvas de sensibilidade, a técnica possibilita calibrar os coeficientes de um modelo linear do SEP e, consequentemente, descrever de forma precisa a resposta da velocidade do gerador em análise. No segundo método, uma técnica de filtragem é utilizada (filtro de Kalman Unscented) a qual fornece uma estimativa adequada para a velocidade angular do rotor mesmo quando elevadas discrepâncias são observadas entre a saída do modelo simulado e a resposta amostrada no sistema real. Os resultados obtidos sobre diferentes sistemas testes evidenciam a eficiência da abordagem proposta. / In this thesis, an approach is proposed to estimate the rotor speed of synchronous generators connected to an electric power system (EPS), from signals that can be easily sampled by measuring equipment, such as current and voltage in high voltage side of the step-up transformer of the power plant. Accurate information about the dynamic behavior of system is essential for effective control and reliable operation of EPS, especially with the increasing complexity of the grid. Hence, the main aim of this work is to provide an estimate of the rotor speed signal that can be applied in the area of small-signal stability, in order to mitigate the detrimental effects of poorly damped electromechanical oscillations in EPSs. The developed approach is composed of two methods, where each of them is applicable depending on the characteristics of the problem to be solved and the available information. In the first method, a trajectory sensitivity technique is applied on the mismatch between the simulated output in the system linear model and the response of the real system. Using this error signal and the sensitivity curves, this method allows to identify and to calibrate some coefficients of the linear model and, consequently, to adequately describe the speed response of the generator under analysis. In this second method, a filtering technique is used, the Unscented Kalman Filter, which provides an adequate estimate for rotor speed even when high discrepancies are observed between the linear model and the sampled response of real system. The results obtained on test systems with different characteristics show the efficiency of the proposed approach.

Alternative energy resources (such as photovoltaics, fuel cells, wind turbines, micro-turbines, and internal combustion engines) and energy storage systems (such as batteries, supercapacitors, and flywheels) are increasingly being connected to the utility grid, creating distributed energy resources which require the implementation of an effective distributed power management strategy. Parallel-connected power converters form a critical component in such a distributed energy resources system. This dissertation addresses small-signal modeling and analysis of parallel-connected power converter systems operating in distributed energy environments. This work focuses on DC-DC and DC-AC power converters. First, this work addresses the small-signal modeling and analysis of parallel-connected power converters in a battery/supercapacitor hybrid energy storage system. The small-signal model considers variations in the current of individual energy storage devices and the DC bus voltage as state variables, variations in the power converter duty cycles as control variables, and variations in the battery and the supercapacitor voltages and the load current as external disturbances. This dissertation proposes several different control strategies and studies the effects of variations in controller and filter parameters on system performance. Simulation studies were carried out using the Virtual Test Bed (VTB) platform under various load conditions to verify the proposed control strategies and their effect on the final states of the energy storage devices. Control strategies for single DC-AC three-phase power converters are also identified and investigated. These include a novel PV (active power and voltage) control with frequency droop control loop, PQ (active power and reactive power) control, voltage control, PQ control with frequency droop control, and PQ control with voltage and frequency droop control. Small-signal models of a three-phase power converter system with these control strategies were developed, and the impact of parameter variations on the stability of a PV controlled converter were studied. Moreover, a small-signal model of parallel-connected three-phase DC-AC power converters with individual DC power supplies and network is proposed. The simulations carried out in stand-alone and grid-connected modes verify the combined control strategies that were developed. In addition, a detailed small-signal mathematical model that can represent the zero-sequence current dynamics in parallel-connected three-phase DC-AC power converters that share a single DC power source is presented. The effects of a variety of factors on the zero-sequence current are investigated, and a control strategy to minimize the zero-sequence current is proposed. Time-domain simulation studies verify the results. Simulations of a parallel-connected DC-AC power converter system with nonlinear load were carried out. The active power filter implemented in this system provides sharing of harmonic load between each power converter, and reduces harmonic distortion at the nonlinear load by harmonic compensation.

The number of large-scale wind farms integrated to the power system in Sweden is increasing. Two generator concepts that are widely used are Doubly-Fed Induction Generators (DFIG) and Full Power Converters (FPC). The study is of a quantitative character and the aim of the Master thesis is to compare DFIG-models with FPC-models integrated in an area with high concentration of hydropower. Then it is possible to examine how the dynamics in the power system change depending on the selection of technology (DFIG or FPC) when connecting a wind farm. The power system is simulated during a summer night, i.e., a low load is connected. The Master thesis covers stability analysis of the power system by using rotor angle stability that are split into small-signal stability and transient stability (time-domain simulations) and finally voltage stability to see how the hydropower generators react when varying the power production in the wind farm. The Master thesis concludes that independently of wind turbine technique, integration of a wind farm has slight impact on the stability in the power system compared to a power system without a wind farm, even though the load is low. Further, an integration of a wind farms affects the reactive power production in neighbouring hydropower plants. Finally, when increasing the size of the wind farm the neighbouring hydropower station consume less reactive power which can induce problem with the voltage stability.

This paper introduces a high-gain, low-noise band-pass filter system for detection/amplification of small signals. In addition, related theory and methodology are described for a specific design implementation. Simulation and experimental results are presented and discussed. The purpose of the implemented design was to construct a band-pass filter system with 102 dB gain and with an output noise level of less than 0.8V. The design of the high-gain band-pass filter system was achieved mainly with the help of Filter Pro, LTSpice IV, and Multisim 12. The thesis provides important support for the project Marker Locator and constitutes a valuable reference for future active filter system design and small signal detection/amplification. / Marker Locator

The focus of this research is on deriving small signal stability models for different Flexible AC Transmission Systems devices by introducing a simple systematic method that is applicable to any dynamic device. Two different small signal models for Unified Power Flow Controllers are introduced. One model is called the power control mode and the other model is the voltage control mode. The two models are compared from transient stability point of view to show the necessity of developing both models for UPFC. The thesis also shows how to derive the small signal stability model of Static Synchronous Compensator, as the shunt branch of UPFC. The small signal stability models of both devices are then validated to ensure the accuracy of the derived models. STATCOM and UPFC power control mode are validated against PSCAD. The UPFC voltage control mode is validated against nonlinear solution of system equations.

The focus of this research is on deriving small signal stability models for different Flexible AC Transmission Systems devices by introducing a simple systematic method that is applicable to any dynamic device. Two different small signal models for Unified Power Flow Controllers are introduced. One model is called the power control mode and the other model is the voltage control mode. The two models are compared from transient stability point of view to show the necessity of developing both models for UPFC. The thesis also shows how to derive the small signal stability model of Static Synchronous Compensator, as the shunt branch of UPFC. The small signal stability models of both devices are then validated to ensure the accuracy of the derived models. STATCOM and UPFC power control mode are validated against PSCAD. The UPFC voltage control mode is validated against nonlinear solution of system equations.

Made available in DSpace on 2014-06-11T19:30:50Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-08-21Bitstream added on 2014-06-13T19:19:29Z : No. of bitstreams: 1 pereira_als_dr_ilha.pdf: 1505539 bytes, checksum: 8b3fa09211b5f80a63a93c6fd21675aa (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este trabalho apresenta estudos referentes à inclusão do dispositivo FACTS STATCOM e a utilização de Redes Neurais Artificiais para o ajuste dos parâmetros de sinais adicionais estabilizantes (PSS’s e POD’s) no sistema de potência multimáquinas. O objetivo é a melhoria da estabilidade frente às pequenas perturbações do sistema de energia elétrica. O modelo matemático utilizado para o estudo das oscilações eletromecânicas de baixa freqüência em sistemas de energia elétrica foi o Modelo de Sensibilidade de Potência (MSP), modificado para permitir a inclusão do dispositivo STATCOM. Este modelo baseia-se no princípio de que o balanço de potência ativa e reativa deve ser satisfeito continuamente em qualquer barra do sistema durante um processo dinâmico. Prosseguindo na realização do trabalho foram desenvolvidos os modelos matemáticos para a inclusão dos PSS’s e POD’s no sistema elétrico, bem como foi realizada uma discussão a respeito da escolha do local de instalação destes controladores e técnicas clássicas para o ajuste de seus parâmetros. A partir disto foram utilizadas redes neurais artificiais (RNA’s) com o objetivo de ajustar os parâmetros dos controladores. A rede utilizada para este fim foi a do tipo Perceptron Multicamadas, sendo utilizado para o seu treinamento o algoritmo Backpropagation. Simulações foram realizadas e os resultados obtidos para os sistemas testes Sul Brasileiro, Simétrico de Duas Áreas e New England são comentados / This work presents studies about the inclusion of FACTS STATCOM devices using neural networks tune stability additional signal parameters (PSS’s and POD’s) on a multi-machine power system. The objective is to improve the stability to small perturbations in electric power systems. The mathematical model used for studying the lower frequency electromechanical oscillations is the Power Sensitivity Model (PSM), modified to allow the inclusion of the STATCOM device. This model is based on the principle that the active and reactive power balance must be continuously satisfied in every bus of the system during the dynamical process. Mathematical models were developed to include the PSS’s and POD’s on the electrical system, as well as the local to install these control devices and the classical techniques to adjust these parameters. Afterwards, the neural networks were used to adjust the parameters of the controllers. The neural network used is a Perceptron Multi Layer, with the training by backpropagation. Simulations were effectuated for the South Brazilian Power System, the Two Areas Symmetrical Power System and the New England Power System

Orientador: Percival Bueno de Araujo / Banca: Carlos Roberto Minussi / Banca: Laurence Duarte Colvara / Banca: Roberto Apolonio / Banca: Vivaldo Fernando da Costa / Resumo: Este trabalho apresenta estudos referentes à inclusão do dispositivo FACTS STATCOM e a utilização de Redes Neurais Artificiais para o ajuste dos parâmetros de sinais adicionais estabilizantes (PSS's e POD's) no sistema de potência multimáquinas. O objetivo é a melhoria da estabilidade frente às pequenas perturbações do sistema de energia elétrica. O modelo matemático utilizado para o estudo das oscilações eletromecânicas de baixa freqüência em sistemas de energia elétrica foi o Modelo de Sensibilidade de Potência (MSP), modificado para permitir a inclusão do dispositivo STATCOM. Este modelo baseia-se no princípio de que o balanço de potência ativa e reativa deve ser satisfeito continuamente em qualquer barra do sistema durante um processo dinâmico. Prosseguindo na realização do trabalho foram desenvolvidos os modelos matemáticos para a inclusão dos PSS's e POD's no sistema elétrico, bem como foi realizada uma discussão a respeito da escolha do local de instalação destes controladores e técnicas clássicas para o ajuste de seus parâmetros. A partir disto foram utilizadas redes neurais artificiais (RNA's) com o objetivo de ajustar os parâmetros dos controladores. A rede utilizada para este fim foi a do tipo Perceptron Multicamadas, sendo utilizado para o seu treinamento o algoritmo Backpropagation. Simulações foram realizadas e os resultados obtidos para os sistemas testes Sul Brasileiro, Simétrico de Duas Áreas e New England são comentados / Abstract: This work presents studies about the inclusion of FACTS STATCOM devices using neural networks tune stability additional signal parameters (PSS's and POD's) on a multi-machine power system. The objective is to improve the stability to small perturbations in electric power systems. The mathematical model used for studying the lower frequency electromechanical oscillations is the Power Sensitivity Model (PSM), modified to allow the inclusion of the STATCOM device. This model is based on the principle that the active and reactive power balance must be continuously satisfied in every bus of the system during the dynamical process. Mathematical models were developed to include the PSS's and POD's on the electrical system, as well as the local to install these control devices and the classical techniques to adjust these parameters. Afterwards, the neural networks were used to adjust the parameters of the controllers. The neural network used is a Perceptron Multi Layer, with the training by backpropagation. Simulations were effectuated for the South Brazilian Power System, the Two Areas Symmetrical Power System and the New England Power System / Doutor

Orientador: Percival Bueno de Araujo / Resumo: Neste trabalho é desenvolvido o modelo matemático de sistemas elétricos de potência multimáquinas para avaliar a estabilidade a pequenas perturbações, com a atuação simultânea de diferentes dispositivos FACTS controlando o fluxo de potência. Os FACTS do tipo SSSC e STATCOM são modelados, considerando suas perdas internas, o modelo resultante é acrescentado à resolução do fluxo de potência, considerando que cada dispositivo FACTS controla uma grandeza do sistema. Utilizando da solução do fluxo, das matrizes Ybarra e Jacobiana, e também tensões e potências, estes são empregados ao Modelo de Sensibilidade de Potência, por meio de simulações, é verificada a atuação dos elementos de controle na estabilidade a pequenas perturbações de sistemas multimáquinas. Para acréscimo de amortecimento às oscilações eletromecânicas, são aplicados controladores ESP e POD. A partir da representação de espaço de estados do modelo final, os autovalores resultantes são estudados para avaliar a estabilidade do sistema. Ao final é discutida a atuação individual e conjunta dos dispositivos FACTS na estabilidade, quando aplicados ao controle do fluxo de potência. / Abstract: In this work the mathematical model of multi-machine power electric systems is developed to evaluate the stability to small perturbations, with the simultaneous actuation of different FACTS devices controlling the power flow. The FACTS of type SSSC and STATCOM are modeled, considering their internal losses, the resulting model is added to the resolution of the power flow, considering that each FACTS device controls a quantity of the system. By the solution of the power flux, the Ybus and Jacobian matrices, as well as voltages and powers, these are used to the Power Sensitivity Model, by means of simulations, it is verified the performance of the control elements in the stability to small perturbation of multi-machine systems. For addition of damping to electromechanical oscillations, ESP and POD controllers are applied. From the state space representation of the final model, the resulting eigenvalues are studied to evaluate the stability of the system. At the end, the individual and combined performance of the FACTS devices in the stability, when applied to the control of the power flow, is discussed. / Doutor