Made available in DSpace on 2016-08-17T14:52:56Z (GMT). No. of bitstreams: 1 Jorge Isaac Rodriguez Rodriguez.pdf: 1323419 bytes, checksum: 4200a77bd6a2f02a314bd07b92e57da8 (MD5) Previous issue date: 2005-02-28 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / In this work a framework for development of electric energy systems applications is proposed, on which several methodologies of analysis can be integrated or be adapted. An application of that framework has been developed to quantify the economic aspect for the improvement of power systems dynamic security based on preventive control. The following methodologies have been integrated for this objective: power systems dynamic security assessment, calculation of preventive control measures for dynamic security improvement and economic quantification of the impact caused by the application of those measures. Dynamic security assessment function uses a fast methodology based on transient energy function for contingencies dynamic ranking and a time-domain based methodology for the dynamic evaluation of contingencies. This last function has been implemented using a distributed processing environment. The power system dynamic security level is defined according to heuristic criteria which will determine the need of application of some control measure. The preventive control measures are defined when establishing the maximum limits of generation; those measures are calculated with fast methods without the use of sensitivities. Power system operation feasibility considering the new generation limits is obtained using a non linear optimal power flow program (OPF) with an objective function of load shedding minimization. The new operation condition of the power system is calculated following technical and economic considerations with the use of an OPF for several objective functions. The framework was projected using object-oriented methodology and CORBA (common object request broker architecture) architecture and has been coded in C++ and Java languages. Complete implementation of the described methodologies has been successfully tested with the Anderson-Fouad WECC-3 generators system and with a configuration of 44 generators of the interconnected Brazilian system. Analysis of results indicates that preventive control allows an improvement of power system dynamic security and a corresponding reduction in the economic impact after the occurrence of severe disturbances. / Neste trabalho é proposto um framework para desenvolvimento de aplicações elétricas, sobre o qual podem ser implementadas ou adaptadas distintas metodologias de análise, conseguindo que trabalhem em forma integrada para a quantificação do impacto econômico da melhoria da segurança dinâmica de sistemas elétricos. As metodologias incluem a avaliação da segurança dinâmica de sistemas de energia elétrica, o cálculo de medidas de controle preventivas para a melhoria dos níveis de segurança dinâmica e a quantificação do impacto econômico produzido pela aplicação de ditas medidas. Na avaliação da segurança dinâmica utiliza-se uma metodologia baseada na função de energia transitória para o ordenamento dinâmico de contingências e uma metodologia baseada no domínio do tempo para a avaliação dinâmica de contingências, esta última dentro de um ambiente de processamento paralelo. O nível de segurança dinâmica do sistema é estabelecido seguindo critérios heurísticos que determinarão a necessidade da aplicação de alguma medida de controle. As medidas de controle preventivo são definidas ao estabelecer os limites máximos de geração, calculados com métodos rápidos, sem o uso de sensibilidades. A factibilidade da operação do sistema considerando estes novos limites de geração é obtida com a utilização de um fluxo de potência ótimo não linear (FPO) e uma função objetivo de minimização de corte de carga. O novo ponto de operação é calculado segundo considerações técnico - econômicas com a utilização de um FPO para diferentes funções objetivo. O framework foi projetado utilizando metodologia orientada a objetos e uma arquitetura CORBA (common object request broker architecture), e codificado nas linguagens C++ e Java. A implementação total das metodologias descritas foi testada com sucesso no sistema Anderson-Fouad WECC de 3 geradores e numa configuração do sistema interligado brasileiro de 44 geradores. A análise dos resultados indica que o controle preventivo permite uma melhoria da segurança dinâmica do sistema de potência e uma correspondente diminuição no impacto econômico após a ocorrência de perturbações severas.

[pt] Esta dissertação trata do problema da agregação dinâmica de modelos de estabilizadores com dupla entrada, aplicados em reguladores de tensão de unidades geradoras coerentes, visando o cálculo de equivalentes dinâmicos precisos para estudos de estabilidade transitória de sistemas de energia elétrica. A metodologia utilizada para o cálculo de equivalentes dinâmicos é baseada em coerência de geradores, e apresenta três etapas básicas: a identificação de unidades geradoras coerentes, a redução estática da rede externa, e a agregação dinâmica dos geradores de cada grupo formado. A agregação dinâmica de um grupo de unidades geradoras coerentes permite a formação de uma ou mais unidades geradoras equivalentes. Haverá um modelo equivalente para cada componente da unidade geradora, ou seja, modelos equivalentes de máquina síncrona, sistema de excitação, estabilizador, turbina e regulador de velocidade. O ajuste numérico dos parâmetros lineares da função de transferência equivalente é feito pelo método de Levenberg-Marquardt, de modo a minimizar o erro entre a resposta em freqüência desta função e a da função de transferência agregada, que representa a soma das funções de transferência individuais das unidades de cada grupo. Isto caracteriza um problema de otimização multivariável. As respostas em freqüência são apresentadas em diagramas de Bode (módulo e fase). A avaliação do desempenho dinâmico dos equivalentes é feita no sistema teste New England, comparando-se as curvas de oscilação dos geradores do sistema interno obtidas em simulações com a rede completa e com o equivalente. Os modelos de estabilizadores com dupla entrada utilizados são do banco de dados do sistema elétrico brasileiro. / [en] This dissertation deals with the problem of dynamic aggregation of dualinput stabilizer models applied on voltage regulators of coherent generating units to calculate dynamic equivalents for power system transient stability studies. The methodology used for the calculation of coherency-based dynamic equivalents has three basic steps: the identification of the coherent groups of generating units, the network reduction and the dynamic aggregation of coherent generator models. The dynamic aggregation of a group of coherent generating units attached to a common busbar consists of the representation of this group by one or more equivalent generating units. There will be an equivalent model for each component of the generating unit, i.e., an equivalent model for the synchronous machine, other one for the excitation system, and so on. The linear parameters of the equivalent transfer function are numerically adjusted to match the frequency response of the corresponding aggregated transfer function which represents the sum of the individual transfer functions for each coherent group. This characterises a multivariable optimization problem. The frequency responses are presented in Bode diagrams (magnitude and phase). The dynamic equivalents are evaluated in the New England system. The swing curves of the internal system generators obtained with the complete system are compared with those obtained with the equivalent system. The dual-input power system stabilizer models considered in this work are in the Brazilian system stability database.

Wind power installations have seen a significant rise all over the world in the past decade. Further significant growth is expected in the future. The UK’s ambitions for offshore wind installations are reflected through Round 1, 2 and 3 projects. It is expected that Round 3 alone will add at least 25 GW of offshore wind generation into the system. Current research knowledge is mostly limited to smaller wind farms, the aim of this research is to improve offline and online modelling techniques for large offshore wind farms. A critical part of offline modelling is the design of the wind farm. Design of large wind farms particularly requires careful consideration as high capital costs are involved. This thesis develops a novel methodology which leads to a cost-effective and reliable design of an offshore wind farm. A new industrial-grade software tool is also developed during this research. The tool enables multiple offshore wind farm design options to be built and tested quickly with minimal effort using a Graphical User Interface (GUI). The GUI is designed to facilitate data input and presentation of the results. This thesis also develops an improved method to estimate a wind farm’s energy yield. Countries with large-scale penetration of wind farms often carry out wind energy curtailments. Prior knowledge of estimated energy curtailments from a wind farm can be advantageous to the wind farm owner. An original method to calculate potential wind energy curtailment is proposed. In order to perform wind energy curtailments a network operator needs to decide which turbines to shut down. This thesis develops a novel method to identify turbines inside a wind farm that should be prioritised for shut down and given priority when scheduling preventive maintenance of the wind farm. Once the wind farm has been built and connected to the network, it operates as part of a power system. Real-time online simulation techniques are gaining popularity among system operators. These techniques allow operators to carry out simulations using short-term forecasted wind conditions. A novel method is proposed to probabilistically estimate the power production of a wind farm in real-time, taking into account variation in wind speed and effects of turbulence inside the wind farm. Furthermore, a new probabilistic aggregation technique is proposed to establish a dynamic equivalent model of a wind farm. It determines the equivalent number and parameters of wind turbines that can be used to simulate the dynamic response of the wind farm throughout the year.

Orientador: Carlos Roberto Minussi / Resumo: Apresenta-se um modelo matemático, baseado na análise de sensibilidade, para a realização de controle de segurança dinâmica para a melhoria da estabilidade transitória de sistemas elétricos de potência. O controle de segurança dinâmica implementado consiste na alteração da impe-dância do sistema elétrico pela retirada/inclusão de linhas de transmissão. A proposta consiste em determinar um modelo de sensibilidade da margem de segurança do sistema em relação à admitância (impedância) do elemento considerado. Deste modo, pode-se estimar o impacto que as alterações no sistema de transmissão podem causar sobre a estabilidade transitória do sistema. Com as devidas adaptações, os resultados aqui apresentados podem ser estendidos para o caso do uso de dispositivos FACTS. A análise da estabilidade é realizada, via uso do conceito de sensibilidade da margem de segurança do sistema, que é determinada pelo Méto-do Direto de Lyapunov, por meio da função de energia total do sistema. Trata-se de um resul-tado que visa dar maior suporte ferramental aos planejadores e aos operadores dos sistemas de energia elétrica. Visando ilustrar os resultados auferidos com a aplicação do modelo proposto, são apresentados os resultados via simulações considerando-se dois sistemas de energia elétri-ca (sistema de 9 barras / sistema clássico Anderson & Fouad, e uma versão do sistema sul bra-sileiro). / Abstract: This work presents a mathematical model based on sensitivity analysis for the implementation of Security Dynamic Control for improvement of transient stability of electric power systems. The Security Dynamic Control performed corresponds to system impedance change by out-put/input of transmission lines (TL’s). The propose aims to determine a sensitivity model for the security margin of the system in relation to the impedance (susceptance) of the considered element. Thus, it is possible estimate the influence of TL’s on transient stability. Considering adaptations and some simplifications, the results obtained with this proposal can be used for FACTS devices. The stability analysis is achieved using the Security Margin concept deter-mined by the direct Lyapunov (energy) method; it is a supporting tool to the planners and op-erators of electric power systems. In order to illustrate the results obtained with the application of the proposed model, the simulation results are presented considering two electric power systems (9-bus system / Anderson & Fouad classic system, and one version of the South Bra-zilian system). / Doutor

In this thesis, controllers for power oscillation damping, transient stability improvement and power flow control by means of a Controlled Series Compensator (CSC) and and a Dynamic Power Flow Controller (DPFC) are proposed. These devices belong to the group of power system components referred to as Flexible AC Transmission System (FACTS) devices. The developed controllers use only quantities measured locally at the FACTS device as inputs, thereby avoiding the risk of interrupted communications associated with the use of remote signals for control. For power systems with one dominating, poorly damped inter-area power oscillation mode, it is shown that a simple generic system model can be used as a basis for damping- and power flow control design. The model for control of CSC includes two synchronous machine models representing the two grid areas participating in the oscillation and three reactance variables, representing the interconnecting transmission lines and the FACTS device. The model for control of DPFC is of the same type but it also includes the phase shift of the internal phase-shifting transformer of the DPFC. The key parameters of the generic grid models are adaptively set during the controller operation by estimation from the step responses in the FACTS line power to the changes in the line series reactance inserted by the FACTS device. The power oscillation damping controller is based on a time-discrete, non-linear approach which aims to damp the power oscillations and set the desired power flow on the FACTS line by means of two step changes in the line reactance separated in time by half an oscillation cycle. A verification of the proposed controllers was done by means of digital simulations using power system models of different complexities. The CSC and DPFC controllers were shown to significantly improve the small-signal- and transient stability in one four-machine system of a type commonly used to study inter-area oscillations. The CSC controller was also tested for 18 different contingencies in a 23-machine system, resulting in an improvement in both the system transient stability and the damping of the critical oscillation mode. / QC 20101112

The research is motivated by the need to address two major challenges in wind power integration: how to mitigate wind power fluctuation and how to ensure stability of the farm and host grid. It is envisaged that wind farm power output fluctuation can be reduced by using a specific type of buffer, such as an energy storage system (ESS), to absorb its negative impact. The proposed solution, therefore, employs ESS to solve the problems. The key research findings include a new technique for calculating the desired power output profile, an ESS charge-discharge scheme, a novel direct-calculation (optimization-based) method for determining ESS optimal rating, and an ESS operation scheme for improving wind farm transient stability. Analysis with 14 wind farms and a compressed-air energy storage system (CAES) shows that the charge-discharge scheme and the desired output calculation technique are appropriate for ESS operation. The optimal ESSs for the 14 wind farms perform four or less switching operations daily (73.2%-85.5% of the 365 days) while regulating the farms output variation. On average, the ESSs carry out 2.5 to 3.1 switching operations per day. By using the direct-calculation method, an optimal ESS rating can be found for any wind farm with a high degree of accuracy. The method has a considerable advantage over traditional differential-based methods because it does not require knowledge of the analytical form of the objective function. For ESSs optimal rating, the improvement in wind energy integration is between 1.7% and 8%. In addition, a net increase in grid steady-state voltage stability of 8.3%-18.3% is achieved by 13 of the 14 evaluated ESSs. For improving wind farm transient stability, the proposed ESS operation scheme is effective. It exploits the use of a synchronous-machine-based ESS as a synchronous condenser to dynamically supply a wind farm with reactive power during faults. Analysis with an ESS and a 60-MW wind farm consisting of stall-regulated wind turbines shows that the ESS increases the farm critical clearing time (CCT) by 1 cycle for worst-case bolted three-phase-to-ground faults. For bolted single-phase-to-ground faults, the CCT is improved by 23.1%-52.2%. / text

The issue of angle instability has been widely discussed in the power engineering literature. Many control techniques have been proposed to provide the complementary synchronizing and damping torques through generators and/or network connected power apparatus such as FACTs, braking resistors and DC links. The synchronizing torque component keeps all generators in synchronism while damping torque reduces oscillations and returns the power system to its pre-fault operating condition. One of the main factors limiting the transfer capacity of the electrical transmission network is the separation of the power system at weak links which can be understood by analogy with a large spring-mass system. However, this weak-links related problem is not dealt with in existing control designs because it is non-trivial during transient period to determine credible weak links in a large power system which may consist of hundreds of strong and weak links. The difficulty of identifying weak links has limited the performance of existing controls when it comes to the synchronization of generators and damping of oscillations. Such circumstances also restrict the operation of power systems close to its transient stability limits. These considerations have led to the primary research question in this thesis, "To what extent can the synchronization of generators and damping of oscillations be maximized to fully extend the transient stability limits of power systems and to improve the transfer capacity of the network?" With the recent advances in power electronics technology, the extension of transfer capacity is becoming more readily achievable. Complementary to the use of power electronics technology to improve transfer capacity, this research develops an improved control strategy by examining the dynamics of the modes of separation associated with the strong and weak links of the reduced transmission network. The theoretical framework of the control strategy is based on Energy Decomposition and Unstable Equilibrium Points. This thesis recognizes that under extreme loadings of the transmission network containing strong and weak links, weak-links are most likely to dictate the transient stability limits of the power system. We conclude that in order to fully extend the transient stability limits of power system while maximizing the value of control resources, it is crucial for the control strategy to aim its control effort at the energy component that is most likely to cause a separation. The improvement in the synchronization amongst generators remains the most important step in the improvement of the transfer capacity of the power system network.

This work presents new analytical and computational methods for operation security assessment of electric power systems by considering Angle and Voltage Stability Limits. In the context of Angle Stability, it was developed a method for estimating transient security margins based on equivalent network reduction techniques and coherent generators. The angle speed deviation was the criterion used to identify generators that swing together. The reduced order was accomplished by replacing two clusters of coherent generators by an One-Machine Infinite Bus equivalent system. With this equivalent, critical fault clearing times and security margins are calculated with the aid of the Equal Area Criterion. The results were in a good agreement when compared with others methods, especially those based on Transient Energy Function used as a Lyapunov function. The method was also applied for estimating security margins and critical fault clearing times of power systems in the presence of wind power generation. It was demonstrated that the proposed method can be used to select critical contingencies, where detailed power system models are needed such that it can reproduce the actual behavior of the system. With respect to Voltage Stability, it was developed an analytical and computational method for steady state voltage stability analysis on a P-Q plane. First of all, it was applied on a simple two-bus power system, and the analytical and computational results were compared. Then, a Voltage Stability Index was derived, in order to obtain the security margins of each bus for any operational state of an n-bus power system. It was carried out by using a power system reduction technique. With the Voltage Stability Index, it is possible to identify critical buses and the regions that are prone to voltage collapse. The voltage stability limits of a distribution power system was also analyzed by means of the P-Q curves, by considering different operation scenarios of wind power generation. It was demonstrated that the wind power can contribute to improve the voltage security margins. Finally, the method was applied to a real power system of Companhia Estadual de Distribuição de Energia Elétrica, in the presence of wind power generation. The methods are computationally efficient and suitable for planning, operation and real-time operation of electric power systems. / Este trabalho apresenta novos métodos analíticos e computacionais para a avaliação da segurança da operação de sistemas elétricos de potência considerando os Limites de Estabilidade Angular e de Tensão. No tema Estabilidade Angular, desenvolveu-se um método para a estimativa de margens de segurança transitória baseado em técnicas de redução de redes e geradores coerentes. O desvio de velocidade angular foi o critério usado para identificar geradores que oscilam juntos. A redução foi realizada substituindo-se dois grupos de geradores coerentes por um sistema Equivalente Máquina-Barra Infinita. Com este equivalente, os tempos críticos de abertura de falta e as margens de segurança são calculados com auxílio do Critério das Áreas Iguais. Os resultados encontrados foram muito satisfatórios quando comparados com aqueles obtidos por outros métodos, especialmente os que utilizam a função energia como função de Lyapunov. O método também foi aplicado para a estimativa de margens de segurança e tempos críticos de abertura de falta, em sistemas de potência na presença de geração eólica. Foi demonstrado que o método proposto é capaz de selecionar contingências críticas que precisam ser estudadas com modelos completos de modo a reproduzir o comportamento real do sistema elétrico. Com relação à Estabilidade Tensão, foi desenvolvido um método analítico e computacional para análise de estabilidade estática de tensão no plano P-Q. Primeiramente, o método foi aplicado em um sistema de potência simples com duas barras, e os resultados analíticos e computacionais foram comparados. Então, um Índice de Estabilidade de Tensão foi deduzido, para determinar a margem de segurança de cada barra para qualquer estado de operação de um sistema de potência com n-barras. Com o Índice de Estabilidade de Tensão, é possível identificar barras críticas e regiões com tendência ao colapso de tensão. Os limites de estabilidade de tensão de um sistema de distribuição foram analisados através das curvas P-Q , no qual foram considerados diferentes cenários de operação da geração eólica. Deste modo, foi demonstrado que a geração eólica pode contribuir para melhorar as margens de segurança de tensão. Finalmente, o método foi aplicado em um sistema de potência real pertencente à Companhia Estadual de Distribuição de Energia Elétrica. Os métodos desenvolvidos são computacionalmente eficientes e adequados para o planejamento da expansão e operação, bem como na operação em tempo real dos sistemas elétricos de potência.

[pt] O incremento de geração fotovoltaica de grande porte traz consideráveis mudanças nas características operativas e dinâmicas do sistema quando este é submetido a grandes distúrbios. Um dos problemas técnicos mais relevantes é a estabilidade transitória, já que a geração intermitente ligada ao sistema por conversores eletrônicos não contribui para o aumento da inércia total do sistema. Entretanto, os conversores eletrônicos podem, potencialmente, trazer novas oportunidades de controle rápido para dar suporte aos geradores síncronos em resposta a um distúrbio severo. No presente trabalho propõe uma estratégia de controle para inversores fotovoltaicos baseado na injeção da corrente com um grande impacto na resposta transitória do ângulo do rotor da máquina síncrona, identificada através da análise de sensibilidade dos autovalores e dos fatores de participação. Ao fazer isso, é possível aumentar a potência ativa da máquina síncrona próximo do seu valor pré-falta, reduzindo o desequilíbrio entre o torque elétrico e mecânico. A estratégia de controle proposta foi testada experimentalmente, utilizando um inversor e uma montagem máquina síncrona-motor e, através da simulação de um sistema híbrido com um sistema fotovoltaico de grande porte. Os resultados mostram que a estratégia de controle proposta não está apenas em conformidade com os requisitos dos código da rede para melhorar a estabilidade da tensão durante uma perturbação grave, mas também é capaz de manter a estabilidade transitória da rede provando, assim, ser uma melhor alternativa em relação à capacidade FRT requerida pelos códigos de rede. / [en] The increase in photovoltaic generation has caused changes in the power system s operative and dynamic characteristics when subjected to severe disturbances. One of the most relevant problems associated with this renewable energy source is the transient stability, as renewable generation connected to the system by electronic converters does not contrinute to the increase of the total inertia of the system. However, electronic converters can potentially bring new opportunities for rapid control to support synchronous generators in response to severe disturbance. The present work proposes a control strategy for photovoltaic inverters based on the injection of the current with a major impact on the transient response of the synchronous machine rotor angle, identified through the eigenvalue sensitivity analysis and the participation factors. By doing so, it is possible to increase the synchronous machine active power output close to its pre-fault value, reducing the disequilibrium between mechanical and electrical torque. The proposed control strategy was experimentally tested using an inverter and a synchronous-motor machine assembly and, by simulating a hybrid system with a large photovoltaic system. The results show that the proposed control strategy not only conforms to the grid codes requirements to improve voltage stability during a severe disturbance, but is also able to maintain transient stability thus proving to be a better alternative to the FRT capability required by the grid codes.