[pt] A estabilidade de tensão tornou-se nos últimos anos tema de intensa pesquisa, envolvendo principalmente a identificação da natureza do problema e a busca de estratégias mais favoráveis para a operação e planejamento dos sistemas de potência. Este trabalho apresenta um relato da evolução da análise do fenômeno sendo, posteriormente descritos os detalhes de sua abordagem através da teoria das bifurcações em sistemas dinâmicos não-lineares. São caracterizados o limite de transmissão de potência à estabilidade de tensão e a geometria das trajetórias no espaço de estados em pontos de equilíbrio em suas proximidades. O estabelecimento de equivalência entre os modelos dinâmico e estático tornou possível o emprego de métodos baseados nas equações algébricas do fluxo de carga na determinação do limite de estabilidade de tensão e na avaliação do comportamento dinâmico local. Com base no algoritmo de fluxo de carga convencional, foi desenvolvido um programa computacional que emprega o método de continuação parametrizado. Os métodos de continuação permitem a obtenção do conjunto completo das soluções reais, relacionadas por um parâmetro escalar, de um sistema de equações. Mostra-se que a aplicação desses métodos em conjunto com as técnicas de análise modal resulta em uma forma eficiente para a seleção e localização de reforços visando aumentar a capacidade global de transmissão dos sistemas de potência. / [en] In the past few years voltage stabiity has become a subject of intense research involving the identification of the nature of this problem and the seek of suitable strategies for power systems operation and planning. In this work it is presented a report on the evolution in the analysis of this phenomena and it is described the details of its approach through the dynamic nonlinear systems bifurcation theory. The power transmission limit imposed by the voltage stability conditions is addressed and the geometry of the trajectories in state space considering the equilibrium points on the vicinity of this limit is deeply studied. The establishment of the equivalence conditions between the dynamic and static power system models made it possible to employ load-flow algebraic equations based methods on both the determination of the power transmission limit and the evaluation of local dynamic behaviour. A load-flow based computer program which uses the parameterized continuation method was developed. The continuation methods are widely known for providing the determination of whole set of a system s solutions which are related by a scalar parameter. In the closure, it is shown that the application of these methods, in a complementary basis with the modal analysis techniques, results in an efficient procedure to promote the choice and location of devices to improve the power system global tranmission capacity.

[pt] Esta dissertação apresenta uma metodologia para a correção do perfil de tensão dos barramentos de um sistema elétrico de potência. Esta correção corresponde a um redespacho de potência reativa efetuada através de mudança das tensões-base nas barras com geração variável de potência reativa, da mudança dos tapes dos transformadores, e do chaveamento de bancos de capacitores/reatores em paralelo. O método consiste na resolução da equações nodais não lineares de fluxo de carga e das equações associadas aos limites violados. Isto é feito através do método de Newton- Raphson. O modelo linearizado, utilizado em cada iteração do método de Newton-Raphson, é reduzido à parte reativa utilizando- se a técnica de acoplamento implícito com a parte ativa (CRIC) sugerida pro J. Carpentier. Como o sistema linearizado admite infinitas soluções escolheu-se aquela que minimiza o desvio quadrático da tensão de todos os barramentos do sistema e dos tapes dos transformadores. Isto é feito através do uso da matriz inversa generalizada de Moore-Penrose. / [en] This dissertation presents a methodology for correction of the bus voltage profile of an electric power system. This correction corresponds to a redispach of reactive power which is effected by means of voltage set-point changes in buses with variable generation of reactive power, transformer tap changes and shunt capacitors/reactors swithing. The proposed method consists of solving the non-linear power flow equations as well as the equatios associated with violated limits. This is done by using the Newton- Raphson method. The linearized model used in each iteration of the Newton- Raphson method is reduced to the reactive part by means of Carpentier s Reactive Implicit Coupling (CRIC) technique. As the linearized system admits several solutions, it is chosen the one which minimizes the quadratic deviation of all bus voltages and transformer taps. This is done by means of Moore-Penrose generalized inverse matrix.

[pt] Study of the UPCF applied to long lines O avanço da eletrônica de potência e de sua aplicação em Sistemas Elétricos de Potência proporcionaram uma nova tecnologia denominada FACTS - Flexilble AC Transmission Systems . Sob o conceito FACTS, encontram-se encontram-se equipamentos para a compensação da potência reativa, regulação de tensão e controle estático e dinâmico do fluxo de potência ativa em linhas de transmissão. Os equipamentos FACTS atualmente pesquisados vêm apresentando novas perspectivas de controle para os sistemas de potência até então não verificadas com o uso de compensadores convencionais. Dentre os equipamentos FACTS pesquisados está o Compensador Generalizado. O Compensador Generalizado oferece a possibilidade de um controle simultâneo e independente do fluxo de Potência ativa e das tensões nas barras do sistema. O objetivo principal deste trabalho é analisar o funcionamento do Compressor Generalizado em regime permanente aplicado a linhas longas. É avaliado sua situação operando numa linha de 2400 km. Dois casos extremos foram abordados: compensação sob carga nominal e compensação sob rejeição de carga. Os resultados obtidos com o Compensador Generalizado foram comparados com os resultados prévios obtidos através de uma compensação realizada com o uso de capacitores série e reatores em derivação. Desta forma, foram verificadas as vantagens oferecidas pelo Compensador Generalizado em relação a outros equipamentos e as possibilidades oferecidas aos sistema de transmissão face às novas alternativas de controle de fluxo de potência proporcionadas. / [en] The improvement of power electronics and its application in Power Systems introduced a new technology denominated FACTS - Flexible AC Transmission Systems. The FACTS concept includes equipment for reactive compensation, voltage regulation and static and dynamic control of the active power flow in transmission lines. The FACTS equipment under recent researches is showing new perspectives for power systems controlling, which were not achieved with conventional compensators. Among the researched FACTS equipment, there is the Unified Power Flow Controller. The UPFC provides a simultaneous and independent control of the active power flow and the voltages in the system. The main objective of this study is to analyze the steady state operation of the UPFC applied to long lines, specially the case fo a 2400 km line. Two extreme cases are discussed: compensation under rated load and compensation under load rejection. The obtained results with the UPFC are compared with previous results from a compensation performed with series capacitors and shunt reactors. Thus, this study presents the advantages of the UPFC in regard of other equipment and the possibilities offered to the transmission systems due to the new provided alternatives for power flow controlling.

[pt] Equivalentes estáticos e dinâmicos de sistemas externos representam um importante papel tanto em projeto e planejamento bem como na operação de sistemas de energia elétrica (SEE), devido sobretudo à redução da complexidade do modelo conduzindo à melhoria da análise e do esforço computacional. Além desses aspectos, o uso de equivalentes contorna o problema da capacidade limitada de memória dos sistemas de computação e se enquadra na estrutura física e conceitual dos recentes minicomputadores. O modelo para o fluxo de potência de uma certa área de um sistema interligado exige uma representação satisfatória afim de simular corretamente o comportamento do seu estado permanente. Equivalente estático do sistema externo está diretamente ligado com esta representação. O objetivo do equivalente externo é obter o melhor modelo válido para uma faixa ampla de condições de operação. Os equivalentes dinâmicos são necessários para diferentes estudos em SEE onde o sistema interno é representado em detalhe e o sistema externo é representado pelo equivalente para simular os efeitos interativos do sistema externo no sistema interno para perturbações originadas no sistema interno. O grande valor deste tipo de simplificação reside no reconhecimento fornecido sobre a tendência dinâmica do sistema. Esta pesquisa apresenta métodos para obtenção de equivalentes tanto para estudos de fluxos de potência como de estabilidade transitória. / [en] The external system static and dynamic equivalents play na impotant role in electric power system desing and planning as well as in system operation. This is due to a reduction in modeling complexity leading to a saving in computing effort to analyse the system. In addition to that, the static and dynamic equivalents overcome the computer storage capacity limitation and are also suitable for the recent minicomputers. The load-flow model of a certain are an interconnected system requires a satisfactory representation of the ramaining areas in order to simulate its steady-state behavior correctly. External system static equivalent is concerned with this representation. The objective of external equivalencing is to obtain the best model over a wide range of operating conditions. The external system dynamic equivalents are needed for different system studies where the internal system is represented in detail and the external system is represented by the equivalent to simulate the interaction effects of the external system on the internal system for disturbances originating in the internal system. The greatest value of this type of system simplification lies in the insight it provides about the dynamic tendencing of the system. In this research, the equivalents obtained by the proposed methods are for load-flowand transient stability studies.

[pt] Dia a dia, técnicas mais avançadas são citadas e utilizadas na análise de sistemas de potência. Os métodos de resolução de fluxo de potência têm merecido especial atenção na medida em que são utilizados em diversos estudos. Programas digitais têm sido elaborados especialmente para cada determinada aplicação prática, onde são definidas as necessidades de rapidez de convergência, de requisitos de memória e de confiabilidade da solução, fatores que quase sempre são interdependentes. A introdução de algoritmos de ajuste convencionais e automáticos da solução de um fluxo de potência em um método moderno chamado Rápido desacoplado é o objeto de estudo do presente trabalho. São analisados os seguintes controles: Tensão na barra primária de um transformador com variação de taps sob condições de carga; fluxo de potência ativa entre áreas do sistema; geração de reativos em barras de tensão controlada; tensão em barras de carga; tensão em barras de carga remotas (sem geração de reativos). Para o bom entendimento da necessidade de se escolher o algoritmo adequado, para cada tipo de aplicação prática, são apresentados conceitos de condicionamento, ordenação e fatorização triangular da matriz representativa do sistema de potência em análise. / [en] Today we can see more and more advanced tecniques being used in the power system analysis. Researchers have been giving more attention to the power flow solution methods because they are used in various studies. Specific digital programes have been elaborated for each pratical application, when the necessities of the convergence rate, memory requests and the confiability of the solutions are defined. In the majority of cases, these factors are interdependent. The topic of this paper is the introduction of conventional and authomatic algorithms for adjusted solutions of pawer flow in a modern methos namad Fast Decoupled. The following controls are analysed: Load-Tap-Changing-Tranformer; Phase-Shifter; Area Interchange Control; Reactive Constraints; Voltage Constraints in PQ-Bus and remote-Bus. Concepts of consition, ordenation and trangular factorization of the power system representative matrix are showed in order to emphasize the necessity of selection of the most convenient algorthm for each practical application.

To integrate large volumes of renewables and use electricity more efficiently, many industrial trials are on-going around the world that aim to realize decentralized or hierarchical control of renewable and distributed energy resources, flexible loads and monitoring devices. As the cost and complexity involved in the centralized communications and control infrastructure may be prohibitive in controlling millions of these distributed energy resources and devices, distributed optimization methods are expected to become much more prevalent in the operation of future electric power systems, as they have the potential to address this challenge and can be applied to various applications such as optimal power ow, state estimation, voltage control, and many others. While many distributed optimization algorithms are developed mathematically, little effort has been reported so far on how these methods should actually be implemented in real-world large-scale systems. The challenges associated with this include identifying how to decompose the overall optimization problem, what communication infrastructures can support the information exchange among subproblems, and whether to coordinate the updates of the subproblems in a synchronous or asynchronous manner. This research is dedicated to developing mathematical tools to address these issues, particularly for solving the non-convex optimal power flow problem. As the first part of this thesis, we develop a partitioning method that defines the boundaries of regions when applying distributed algorithms to a power system. This partitioning method quantifies the computational couplings among the buses and groups the buses with large couplings into one region. Through numerical experiments, we show that the developed spectral partitioning approach is the key to achieving fast convergence of distributed optimization algorithms on large-scale systems. After the partitioning of the system is defined, one needs to determine whether the communications among neighboring regions are supported. Therefore, as the second part of this thesis, we propose models for centralized and distributed communications infrastructures and study the impact of communication delays on the efficiency of distributed optimization algorithms through network simulations. Our findings suggest that the centralized communications infrastructure can be prohibitive for distributed optimization and cost-effective migration paths to a more distributed communications infrastructure are necessary. As the sizes and complexities of subproblems and communication delays are generally heterogeneous, synchronous distributed algorithms can be inefficient as they require waiting for the slowest region in the system. Hence, as the third part of this thesis, we develop an asynchronous distributed optimization method and show its convergence for the considered optimal power flow problem. We further study the impact of parameter tuning, system partitioning and communication delays on the proposed asynchronous method and compare its practical performance with its synchronous counterpart. Simulation results indicate that the asynchronous approach can be more efficient with proper partitioning and parameter settings on large-scale systems. The outcome of this research provides important insights into how existing hardware and software solutions for Energy Management Systems in the power grid can be used or need to be extended for deploying distributed optimization methods, which establishes the interconnection between theoretical studies of distributed algorithms and their practical implementation. As the evolution towards a more distributed control architecture is already taking place in many utility networks, the approaches proposed in this thesis provide important tools and a methodology for adopting distributed optimization in power systems.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第16855号 / 工博第3576号 / 新制||工||1540(附属図書館) / 29530 / 京都大学大学院工学研究科電気工学専攻 / (主査)教授 引原 隆士, 教授 木本 恒暢, 教授 小野寺 秀俊 / 学位規則第4条第1項該当

The co-optimization of energy and reserves has become a standard requirement in integrated markets. This is due to the inverse relationship that exists between energy and reserves. The provision of reserves generally reduces the amount of primary energy a generating unit can produce and vice versa. This suggests that these products should be procured through a simultaneous auction to ensure optimal procurement and pricing. Furthermore, forward markets dictate that this co-optimization of energy and reserves be done over a multi-period planning horizon. This dissertation addresses the problem of optimal scheduling and pricing of energy and reserves over a multi-period planning horizon using an optimal power flow formulation. The extension of the problem from a static optimization problem to a dynamic optimization problem is presented. Price definitions for energy and reserves in terms of shadow prices emanating from the optimization algorithm are provided. It is shown that the proposed formulation of prices leads to the cascading of reserve prices and eliminates the problem of “price reversal” where lower quality reserves are priced higher than higher ii quality reserves. Pricing conditions are also established for the downward substitution of higher quality reserves for lower quality reserves. The proposed pricing formulations are tested on the IEEE 24 Bus Reliability Test System and on the South African power network. The simulated results show that cascading of reserve prices does occur and that prices of different types of reserves are equal when downward substitution of reserves occurs. Zonal reserve requirements result in higher energy and reserve prices, which in term result in higher procurement costs to the system operator and higher profits to market participants. Congestion on the network also results in higher procurement costs to the system operator and higher profits to market participants in the case of zonal pricing of reserves. / Dissertation (MEng)--University of Pretoria, 2013. / gm2014 / Electrical, Electronic and Computer Engineering / unrestricted

Transition towards low-carbon energy systems requires an increase in the volume of renewable Distributed Generation (DG), particularly wind and photovoltaic, connected to distribution networks. To facilitate the connection of renewable DG without the need for expensive and time-consuming network reinforcements, distribution networks should move from passive to active methods of operation, whereby technical network constraints are actively managed in real time. This requires the deployment of control solutions that manage network constraints and, crucially, ensure adequate levels of energy curtailment from DG plants by using other controllable elements to solve network issues rather than resorting to generation curtailment only. This thesis proposes a deterministic distribution Network Management System (NMS) to facilitate the connections of renewable DG plants (specifically wind) by actively managing network voltages and congestion in real time through the optimal control of on-load tap changers (OLTCs), DG power factor and, then, generation curtailment as a last resort. The set points for the controllable elements are found using an AC Optimal Power Flow (OPF). The proposed NMS considers the realistic modelling of control by adopting one-minute resolution time-series data. To decrease the volumes of control actions from DG plants and OLTCs, the proposed approach departs from multi-second control cycles to multi-minute control cycles. To achieve this, the decision-making algorithm is further improved into a risk-based one to handle the uncertainties in wind power throughout the multi-minute control cycles. The performance of the deterministic and the risk-based NMS are compared using a 33 kV UK distribution network for different control cycles. The results show that the risk-based approach can effectively manage network constraints better than the deterministic approach, particularly for multi-minute control cycles, reducing also the number of control actions but at the expense of higher levels of curtailment. This thesis also proposes energy storage sizing framework to find the minimum power rating and energy capacity of multiple storage facilities to reduce curtailment from DG plants. A two-stage iterative process is adopted in this framework. The first stage uses a multi-period AC OPF across the studied horizon to obtain initial storage sizes considering hourly wind and load profiles. The second stage adopts a high granularity minute-by-minute control driven by a mono-period bi-level AC OPF to tune the first-stage storage sizes according to the actual curtailment. The application of the proposed planning framework to a 33 kV UK distribution network demonstrates the importance of embedding real-time control aspects into the planning framework so as to accurately size storage facilities. By using reactive power capabilities of storage facilities it is possible to reduce storage sizes. The combined active management of OLTCs and power factor of DG plants resulted in the most significant benefits in terms of the required storage sizes.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2016-01-07T17:13:46Z No. of bitstreams: 1 luizeduardodesouzapereira.pdf: 1798748 bytes, checksum: 8dd5bfcce6449767d768c651966a061d (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2016-01-25T16:52:02Z (GMT) No. of bitstreams: 1 luizeduardodesouzapereira.pdf: 1798748 bytes, checksum: 8dd5bfcce6449767d768c651966a061d (MD5) / Made available in DSpace on 2016-01-25T16:52:02Z (GMT). No. of bitstreams: 1 luizeduardodesouzapereira.pdf: 1798748 bytes, checksum: 8dd5bfcce6449767d768c651966a061d (MD5) Previous issue date: 2015-06-12 / A análise do fluxo de potência determinístico é restrita a um único instante de tempo específico. Contudo, as demandas de potência ativa e reativa, dentre outros, variam constantemente e afetam o perfil das tensões nodais e as distribuições dos fluxos de potência nos ramos do sistema elétrico. Desta forma, a utilização do modelo determinístico seria inviável, face às inúmeras simulações necessárias no sentido de representar todas as possíveis combinações das variações envolvidas no problema. Com a utilização da matemática intervalar é possível representar intervalos de variação das demandas ativa e reativa, dos parâmetros de linha e obter, através de um fluxo de potência intervalar, o perfil das tensões nodais, as distribuições de fluxo de potência nos ramos e as perdas também na forma intervalar. Por conseguinte, é possível realizar uma análise detalhada e completa do comportamento da rede frente às variações em estudo. A proposta do trabalho é modelar e implementar as metodologias de fluxo de potência intervalar, nas versões polar e injeção de correntes, incorporando o controle de geração de reativo em barras PV e o limite de tensão em barras PQ nos vários pontos de operação, incluindo o ponto de máximo carregamento. A simulação de Monte Carlo é utilizada como parâmetro para a aferição dos resultados. / The analysis of the deterministic power flow is restricted to a single time instant. However, the active and reactive load powers, among others, vary constantly and affect the voltage profiles and line flows throughout electric power systems. Therefore, the deterministic model is not feasible due to a number of simulations required to represent all possible combinations of the variations involved in the problem. The interval mathematics can represent ranges of active and reactive power demand. As a result, through an interval power flow, the voltage profile at all nodes, the distribution of power flow in the branches and the losses in the interval form can also be calculated. It is therefore possible to perform a detailed analysis of the network taking into account the uncertainties under study. The purpose of this study is to model and implement the polar and the current injection interval power flow formulations incorporating the reactive power generation control on PV buses and voltage limit control on PQ buses. Various operating points are considered, including maximum loading point. The Monte Carlo simulation is used to validate the proposed methodologies.