Widespread access to renewable electricity is seen as a viable method to mitigate carbon emissions, although problematic are the issues associated with the integration of the generation systems within current power system configurations. Wind power plants are the primary large-scale renewable generation technology applied globally, but display considerable short-term supply variability that is difficult to predict. Power systems are currently not designed to operate under these conditions, and results in the need to increase operating reserve in order to guarantee stability. Often, operating conventional generation as reserve is both technically and economically inefficient, which can overshadow positive benefits associated with renewable energy exploitation. The purpose of this thesis is to introduce and assess an alternative method of enhancing power system operations through the control of electric loads. In particular, this thesis focuses on managing highly-distributed sustainable demand-side infrastructure, in the form of heat pumps, electric vehicles, and electrolyzers, as dispatchable short-term energy balancing resources. The main contribution of the thesis is an optimal control strategy capable of simultaneously balancing grid- and demand-side objectives. The viability of the load control strategy is assessed through model-based simulations that explicitly track end-use functionality of responsive devices within a power systems analysis typically implemented to observe the effects of integrated wind energy systems. Results indicate that there is great potential for the proposed method to displace the need for increased reserve capacity in systems considering a high penetration of wind energy, thereby allowing conventional generation to operate more efficiently and avoid the need for possible capacity expansions. / Graduate

Electric power is a basic requirement for present day life and its various economic sectors. To satisfy the ever-increasing needs for electricity, the number of generating units, transmission lines and distribution systems is rising steadily. In addition, electric power systems are among the most complex industrial systems of the modern age. Beside complexity, the generation of electric power is a main source of gaseous emissions and pollutants. The planning and operation of electric power systems must be done in a way that the load demand is met reliably, cost-effectively and in an environmentally responsible manner. Practitioners strive to achieve these goals for successful planning and operations utilizing various optimization tools. It is clear that the objectives to be satisfied are mostly conflicting. In particular, minimizing the fuel cost and the gaseous emissions are two conflicting and non-commensurate objectives. Therefore, multi-objective optimization techniques are employed to obtain trade-off relationships between these incompatible objective functions in order to help decision makers take proper decisions. In this thesis, two main power system operation problems are addressed. These are the economic load dispatch (ED) and the short-term hydro-thermal generation scheduling (STHTS). They are treated first as single-objective optimization problems then they are tackled as multi-objective ones considering the environmental aspects. These problems, single and multi-objective, are nonlinear non-convex constrained optimization problems with high-dimensional search spaces. This makes them a real challenge for any optimization technique. To obtain the optimal or close to optimal solutions, a modified bacterial foraging algorithm is proposed, developed and successfully applied. The bacterial foraging algorithm is a metaheuristic non-calculus-based optimization technique. The proposed algorithm is validated using diverse benchmark optimization examples before implementing it to solve the problems of this thesis. Various practical constraints are considered in the different cases of each problem. These include transmission losses, valve-point effects for both the ED and the STHTS problems and water availability and reservoir configurations for the STHTS problem. In all cases the optimal or near-optimal solution is obtained. For the multi-objective optimization cases, the Pareto optimal solution set that shows the trade-off relationship between the conflicting objectives is successfully captured.

Wind power installations are growing rapidly throughout the world due to environmental concerns associated with electric power generation from conventional generating units. Wind power is highly variable and its uncertainty creates considerable difficulties in system operation. Reliable operation of an electric power system with significant wind power requires quantifying the uncertainty associated with wind power and assessing the capacity value of wind power that will be available in the operating lead time. This thesis presents probabilistic techniques that utilize time series models and a conditional probability approach to quantify the uncertainty associated with wind power in a short future time, such as one or two hours. The presented models are applied to evaluate the risk of committing electric power from a wind farm to a power system. The impacts of initial wind conditions, rising and falling wind trends, and different operating lead times are also assessed using the developed methods. An appropriate model for day-ahead wind power commitment is also presented. Wind power commitment for the short future time is commonly made equal to, or a certain percentage, of the wind power available at the present time. The risk in meeting the commitment made in this way is different at various operating conditions, and unknown to the operator. A simplified risk based method has been developed in this thesis to assist the operator in making wind power commitments at a consistent level of risk that is acceptable to the system. This thesis presents a methodology to integrate the developed short-term wind models with the conventional power generation models to evaluate the overall operational reliability of a wind integrated power system. The area risk concept has been extended to incorporate wind power, evaluate the unit commitment risk and the well- being indices of a power system for a specified operating lead time. The method presented in this thesis will assist the operator to determine the generator units and the operating reserve required to integrate wind power and meet the forecast load for a short future time while maintaining an acceptable reliability criterion. System operators also face challenges in load dispatch while integrating wind power since it cannot be dispatched in a conventional sense, and is accepted as and when present in current operational practices. The thesis presents a method to evaluate the response risk and determine the unit schedule while satisfying a specified response risk criterion incorporating wind power. Energy storage is regarded as an effective resource for mitigating the uncertainty of wind power. New methods to incorporate energy storage with wind models, and with wind-integrated power system models to evaluate the wind power commitment risk and unit commitment risk are presented in this thesis. The developed methods and the research findings should prove useful in evaluating the operating risks to wind farm operators and system operators in wind integrated power systems.

CoordenaÃÃo de AperfeiÃoamento de NÃvel Superior / Neste trabalho foi desenvolvido o estudo e as aplicaÃÃes das condiÃÃes de estabilidade na operaÃÃo do sistema elÃtrico de potÃncia incorporado em um simulador interativo de usinas termelÃtricas de ciclo combinado, que permita melhorar os processos de treinamento e, consequentemente, o nÃvel de qualidade dos futuros operadores e mantenedores de usinas termelÃtricas, bem como manter atualizados os atuais operadores. Um pequeno conjunto de definiÃÃes e conceitos das Ãreas de âestabilidade, confiabilidade e anÃlise de desempenho de sistemas de potÃnciaâ à apresentado com o objetivo de distinguir a operaÃÃo no sistema de potÃncia. O simulador contempla a modelagem matemÃtica de 3 e 6 ordem das partes fÃsicas e elÃtricas da mÃquina sÃncrona, a modelagem de seus controladores projetados como compensador dinÃmico e mÃtodos numÃricos para a resoluÃÃo da equaÃÃo diferenciais. O cÃlculo dos parÃmetros à realizado atravÃs de um programa desenvolvido com a ferramenta computacional MATLAB e comparados aos implementados em uma UTCC. As simulaÃÃes e validaÃÃo de variaÃÃes dos modelos sÃo realizadas com os programas ANATEM - CEPEL para analisar a eficiÃncia do sistema projetado e avaliar a melhoria do desempenho dinÃmico do sistema. / This work was developed the study and application of conditions of stability in the operation of power system embedded in an interactive simulation of combined cycle power plants that will improve the training processes and therefore the quality of the future operators and maintainers of thermoelectric plants and keep up the current operators. A small set of definitions and concepts in the areas of "stability, reliability and performance analysis of power systems" is presented in order to distinguish the operation in the power system. The simulation includes the modeling of the 6th order of the parts of the physical and electrical synchronous machine, the modeling of its Controlled designed as dynamic and rewarding numerical methods for solving differential equation. The calculation of the parameters is accomplished through a program developed with MATLAB software tool and compared to those implemented at the plant. The simulations and validation of variations of the model are performed with the programs ANATEM - CEPEL to analyze the efficiency of the system designed to evaluate and improve the dynamic performance of the system.

Efficient and reliable techniques for power delivery and utilization are needed to account for the increased penetration of renewable energy sources in electric power systems. Such methods are also required for current and future demands of plug-in electric vehicles and high-power electronic loads. Distributed control and optimal power network architectures will lead to viable solutions to the energy management issue with high level of reliability and security. This dissertation is aimed at developing and verifying new techniques for distributed control by deploying DC microgrids, involving distributed renewable generation and energy storage, through the operating AC power system. To achieve the findings of this dissertation, an energy system architecture was developed involving AC and DC networks, both with distributed generations and demands. The various components of the DC microgrid were designed and built including DC-DC converters, voltage source inverters (VSI) and AC-DC rectifiers featuring novel designs developed by the candidate. New control techniques were developed and implemented to maximize the operating range of the power conditioning units used for integrating renewable energy into the DC bus. The control and operation of the DC microgrids in the hybrid AC/DC system involve intelligent energy management. Real-time energy management algorithms were developed and experimentally verified. These algorithms are based on intelligent decision-making elements along with an optimization process. This was aimed at enhancing the overall performance of the power system and mitigating the effect of heavy non-linear loads with variable intensity and duration. The developed algorithms were also used for managing the charging/discharging process of plug-in electric vehicle emulators. The protection of the proposed hybrid AC/DC power system was studied. Fault analysis and protection scheme and coordination, in addition to ideas on how to retrofit currently available protection concepts and devices for AC systems in a DC network, were presented. A study was also conducted on the effect of changing the distribution architecture and distributing the storage assets on the various zones of the network on the system’s dynamic security and stability. A practical shipboard power system was studied as an example of a hybrid AC/DC power system involving pulsed loads. Generally, the proposed hybrid AC/DC power system, besides most of the ideas, controls and algorithms presented in this dissertation, were experimentally verified at the Smart Grid Testbed, Energy Systems Research Laboratory. All the developments in this dissertation were experimentally verified at the Smart Grid Testbed.

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No. of bitstreams: 1 hevertonreissouza.pdf: 2039435 bytes, checksum: 82a19bf494e9ac400021280fb64ec1ae (MD5) Previous issue date: 2014-02-28 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O Sistema Interligado Nacional (SIN) possui características peculiares que o torna diferente de qualquer outro no mundo, como por exemplo, predominância de usinas hidrelétricas e uma extensa rede de transmissão. Estas características, aliadas a incerteza nas afluências futuras, conduz a necessidade da realização de vários estudos na área de planejamento da operação. O planejamento da operação energética tem por objetivo determinar metas de geração hidráulica e térmica, de forma a atender o mercado consumidor de energia, com confiabilidade e economicidade, utilizando da melhor forma possível os recursos energéticos disponíveis. Para este propósito são utilizados modelos matemáticos que buscam a minimização do custo total esperado de operação do sistema, dentro de um determinado horizonte de planejamento, utilizando diferentes níveis de detalhamento. O objetivo principal deste trabalho é avaliar alguns impactos da modelagem do sistema elétrico no problema de planejamento da operação de médio prazo. Neste sentido, o sistema de transmissão é representado em sua forma completa, através de equações não lineares que modelam os fluxos de potência ativa e reativa em cada circuito que compõe o sistema elétrico. Além disso, são considerados os limites de tensão nas barras, assim como o limite de carregamento dos circuitos para cada patamar de carga. As usinas hidrelétricas e termelétricas são representadas de forma individualizada, e a função de produtibilidade é modelada através de polinômios de quarto grau. O modelo proposto utiliza Funções de Custo Futuro (FCF) pré-calculadas por um programa de planejamento da operação de médio/longo prazo, baseado em sistemas equivalentes de energia. Neste trabalho foram utilizadas as FCF produzidas pelo programa Modelo de Despacho Hidrotérmico (MDDH), desenvolvido pela UFJF. Entretanto, é importante destacar que outro modelo de decisão estratégica, baseado em sistemas equivalentes de energia, poderia ser adotado para gerar as FCF utilizadas neste trabalho. A metodologia proposta neste trabalho foi avaliada através do estudo de casos tutoriais e de médio porte, objetivando demonstrar os impactos da representação do sistema de transmissão no custo total esperado de operação do sistema e diferenças na estratégia de operação do mesmo. / The Brazilian Interconnected System has unique characteristics that make it different of any other in the world, such as predominance of hydroelectric power plants and an extensive transmission system. These features, combined with uncertainty in future inflows, leads to necessity of conducting several studies on planning of the operation. The energy operation planning aims to determine targets for hydraulic and thermal generation to meet the consumer energy market with reliability and economy, as well as possible using the available energy resources. For this purpose mathematical models that aims to minimize the expected total cost of the system operation, within a given planning horizon, using different levels of detail are used. The main objective of this work is to evaluate some impacts of the transmission system modeling in the long-term operation planning problem. In this sense, the transmission system is included in its complete form, using nonlinear equations that model the active and reactive power flow in the electrical system. In addition, some operation limits are considered, such as bus voltage limits and power flow limits in the transmission lines and transformers, for each load level. The hydroelectric and thermoelectric plants are represented in an individual form and the producibility function is modeled by fourth degree polynomials. The proposed model uses cost-to-go functions calculated from a long term operation planning program based on equivalent energy systems. In this work the cost-to-go functions produced by MDDH program were used. This program was developed by the Federal University of Juiz de Fora (UFJF). However, it is important to point out that any other model of strategic decision, based on equivalent energy systems, could be used to generate the cost-to-go functions. The proposed methodology is evaluated and validated through the study of medium scale systems and tutorial systems. The main objective is to demonstrate the impact of the detailed transmission system modeling in the total system operating expected total cost and identify differences in operation strategy.

A proposal for the spinning reserve assessment and allocation for El Salvador¡¦s Deregulated Electricity Market is formulated. Traditionally, the Independent System Operator calculates the spinning reserve as percentage of the forecast demand. And Automatic Generation Control (AGC) is allocated based on the partition factor. The reserve calculation neither reflects consistency achieving its main objective, reliability, nor is optimum performance control reached by the allocating mechanism. In the proposed method, the spinning reserve is estimated taking into account the generators outage ratio and AGC is allocated based on the North American Electric Reliability Corporation¡¦s Control Performance Standard-1. The allocation problem is solved with an improved Particle Swarm Optimization algorithm with a technique to modify the inertial factor on each iteration. The proposed method exhibits better results and it matches the Salvadorian technical requirements and market characteristics.

The main function of the power grid is to transfer electric energy from generating facilities to consumers. To have a reliable and economical supply of electricity, large amounts of electric energy often have to be transferred over long distances. The transmission system has a limited capacity to transfer electric power, called the transfer capacity. Severe system failures may follow if the transfer capacity is reached during operation. Due to uncertainties, such as the random failure of system components, the transfer capacity for the near future is not readily determinable. Also, due to market principles, and reaction times and ramp rates of production facilities, power flow control is not fully flexible. Therefore, a transfer limit, which is below the transfer capacity, is decided and preventative actions are taken when the transfer reaches this limit. In this thesis an approach to deciding an optimal strategy for power flow control through activation of regulating bids on the regulating power market is outlined. This approach leads to an optimal definition of transfer limits as the boundary between the domain where no bid should be activated and the domains where bids should be activated. The approach is based on weighing the expected cost from system failures against the production cost. This leads to a stochastic impulse control problem for a Markov process in continuous time. The proposed method is a novel approach to decide transfer limits in power system operation. The method is tested in a case study on the IEEE 39 bus system, that shows promising results. In addition to deciding optimal transfer limits, it is also investigated how the transfer capacity can be enhanced by controlling components in the power system to increase stability. / QC 20111010