Devido à alta demanda energética e a grande complexidade dos atuais Sistemas Elétricos de Potência (SEPs), altamente interligados, torna-se cada vez mais importante para o operador do sistema, conhecer o estado atual do SEP. Além disso, dispor de ferramentas que permitam prever situações que venham a comprometer o bom funcionamento do sistema. Como um bom funcionamento, enquadra-se a continuidade do suprimento e perfis adequados de tensão elétrica, mesmo após a ocorrência de perturbações, o que pode ser afetado pelo fenômeno de instabilidade de tensão (ou colapso de tensão). Por isso, o objetivo deste trabalho é desenvolver uma metodologia de análise do colapso de tensão em tempo real considerando limites de potência ativa e reativa de geradores, a qual visa auxiliar o operador do sistema. Esta metodologia é dividida em cinco etapas. A primeira delas consiste em uma análise do caso base dos SEPs considerados, utilizando um algoritmo que permite estimar a margem de estabilidade de tensão do sistema, considerando os limites de potência ativa e reativa dos geradores. Esta primeira etapa utiliza a metodologia de fluxo de potência continuado, utilizando a carga e a tensão como parâmetros de continuação. A segunda etapa apresenta uma análise de contingências rápida considerando contingências simples de linhas de transmissão, seguindo o critério N-1. Nesta segunda etapa, foi utilizado o método de Look Ahead Modificado. A terceira etapa é uma análise apurada das contingências mais críticas, identificadas na etapa dois, a fim de verificar a presença de bifurcações induzidas por limites. Nesta terceira etapa, também se utilizou a metodologia de fluxo de potência continuado. Na quarta etapa, são aplicados todos os controle disponíveis no sistema, como inserção de banco de capacitores e ajuste do TAP dos transformadores, a fim de verificar qual seria o impacto dessas ações de controle no limite de operação segura do sistema, utilizando o método de Look Ahead Modificado. Essas quatro etapas possibilitam uma análise da estabilidade de tensão do sistema em tempo real. Por fim, é proposta uma quinta etapa de análise de contingências Offline, sendo uma análise mais precisa de todas as contingências, utilizando a metodologia de fluxo de potência continuado. Os SEPs analisados nesta dissertação foram o sistema de cinco barras Stagg, o sistema de quatorze barras padrão do Institute of Electrical and Electronics Engineers (IEEE) e o sistema de trinta barras padrão IEEE. / Due to the high energy demand and the high complexity of today's interconnected Electrical Power Systems (SEPs), it is becoming increasingly important for the system operator to know the current state of the SEP. In addition, have the tools to predict situations that may compromise the smooth operation of the system. As a good operation, the continuity of the supply and adequate voltage profiles are correct, even after the occurrence of disturbances, which can be affected by the phenomenon of voltage instability (or voltage collapse). Therefore, the objective of this work is to develop a methodology for the analysis of voltage collapse in real time considering the limits of active and reactive power of generators, which aims to assist the system operator. This methodology is divided into five steps. The first one consists of an analysis of the base case of the considered SEPs, using an algorithm that allows estimating the voltage stability margin of the system considering the limits of active and reactive power of the generators. This first step uses the continuous power flow methodology, using load and voltage as continuation parameters. The second stage presents a fast contingency analysis considering simple contingencies of transmission lines, following the criterion N-1. In this second step, the Modified Look Ahead method was used. The third step is an accurate analysis of the most critical contingencies, identified in step two, in order to verify the presence of limits-induced bifurcations. In this third step, we also used the continuous power flow methodology. In the fourth step, all available system controls, such as capacitor bank insertion and TAP adjustment of the transformers, are applied in order to verify the impact of these control actions on the safe operation limit of the system, using the Look Ahead Modified. These four steps enable a real-time analysis of the voltage stability of the system. Finally, a fifth stage of analysis of Offline contingencies is proposed, and a more precise analysis of all the contingencies using the methodology of continuous power flow is proposed. The SEPs analyzed in this dissertation were the Stagg five-bar system, the Institute of Electrical and Electronics Engineers (IEEE) standard fourteen bar system and the IEEE standard thirty-bar system.

Neste trabalho é apresentado um estudo de controladores aplicados a retificadores boost pré reguladores de alto fator de potência. A estratégia convencional, mais utilizada, é o controle por valores médios instantâneos que apresenta uma malha de corrente rápida e uma malha de tensão lenta. A frequência de corte desta última malha é baixa devido a ondulação de tensão de saída no dobro da frequência da rede que deve existir para apresentar uma corrente de entrada com baixa distorção harmônica. Esses controles apresentam um sobressinal elevado e transição lenta durante transitórios de carga, levando a elevação da tensão dos capacitores de saída. A técnica apresentada é um controlador digital com feedforward de potência de saída associado a uma malha de realimentação direta, também conhecido como autocontrole. Essa estratégia possibilita melhores resultados nos transitórios de carga possibilitando redução do capacitor de saída com reduzido sobressinal no transitório de carga. / In this work a study applied in controlled boost rectifiers with high power factor is presented. A most widely used conventional control strategy is the instant average current control, this kind of control have a fast current loop and a slow voltage loop.The cutoff frequency of the voltage loop is low because the output voltage ripple must be twice the frequency of the input network, that need to exist to provide an input current with low harmonic distortion. These controllers feature a high overshoot and a slow transition during the transient load what leads a high voltage in the output capacitors. The developed technique is a digital controller that operate with a feedforward output power associated with one cycle control. This strategy provides better results in the load transient, reducing the overshoot and alloying a reduction of the output capacitor.

Neste trabalho é apresentado um estudo de controladores aplicados a retificadores boost pré reguladores de alto fator de potência. A estratégia convencional, mais utilizada, é o controle por valores médios instantâneos que apresenta uma malha de corrente rápida e uma malha de tensão lenta. A frequência de corte desta última malha é baixa devido a ondulação de tensão de saída no dobro da frequência da rede que deve existir para apresentar uma corrente de entrada com baixa distorção harmônica. Esses controles apresentam um sobressinal elevado e transição lenta durante transitórios de carga, levando a elevação da tensão dos capacitores de saída. A técnica apresentada é um controlador digital com feedforward de potência de saída associado a uma malha de realimentação direta, também conhecido como autocontrole. Essa estratégia possibilita melhores resultados nos transitórios de carga possibilitando redução do capacitor de saída com reduzido sobressinal no transitório de carga. / In this work a study applied in controlled boost rectifiers with high power factor is presented. A most widely used conventional control strategy is the instant average current control, this kind of control have a fast current loop and a slow voltage loop.The cutoff frequency of the voltage loop is low because the output voltage ripple must be twice the frequency of the input network, that need to exist to provide an input current with low harmonic distortion. These controllers feature a high overshoot and a slow transition during the transient load what leads a high voltage in the output capacitors. The developed technique is a digital controller that operate with a feedforward output power associated with one cycle control. This strategy provides better results in the load transient, reducing the overshoot and alloying a reduction of the output capacitor.

In the modern generation, Electric Power has become one of the fundamental needs for humans to survive. This is due to the dependence of continuous availability of power. However, for electric power to be available to the society, it has to pass through a number of complex stages. Through each stage power quality problems are experienced on the grid. Under-voltages and over-voltages are the most common electric problems experienced on the grid, causing industries and business firms losses of Billions of dollars each year. Researchers from different regions are attracted by an idea that will overcome all the electrical issues experienced in the traditional grid using Artificial Intelligence (AI). The idea is said to provide electric power that is sustainable, economical, reliable and efficient to the society based on Evolutionary Algorithms (EAs). The idea is Smart Grid. The research focused on Power Quality Optimization in Smart Grid based on improved Differential Evolution (DE), with the objective functions to minimize voltage swells, counterbalance voltage sags and eliminate voltage surges or spikes, while maximizing the power quality. During Differential Evolution improvement research, elimination of stagnation, better and fast convergence speed were achieved based on modification of DE’s mutation schemes and parameter control selection. DE/Modi/2 and DE/Modi/3 modified mutation schemes proved to be the excellent improvement for DE algorithm by achieving excellent optimization results with regards to convergence speed and elimination of stagnation during simulations. The improved DE was used to optimize Power Quality in smart grid in combination with the reconfigured and modified Dynamic Voltage Restorer (DVR). Excellent convergence results of voltage swells and voltage sags minimization were achieved based on application of multi-objective parallel operation strategy during simulations. MATLAB was used to model the proposed solution and experimental simulations. / Electrical and Mining Engineering / M. Tech. (Electrical Engineering)

Indiana University-Purdue University Indianapolis (IUPUI) / Hydraulic wind power transfer systems deliver the captured energy by the blades to the generators differently. In the conventional systems this task is carried out by a gearbox or an intermediate medium. New generation of wind power systems transfer the captured energy by means of high-pressure hydraulic fluids. A hydraulic pump is connected to the blades shaft at a high distance from the ground, in nacelle, to pressurize a hydraulic flow down to ground level equipment through hoses. Multiple wind turbines can also pressurize a flow sending to a single hose toward the generator. The pressurized flow carries a large amount of energy which will be transferred to the mechanical energy by a hydraulic motor. Finally, a generator is connected to the hydraulic motor to generate electrical power. This hydraulic system runs under two main disturbances, wind speed fluctuations and load variations. Intermittent nature of the wind applies a fluctuating torque on the hydraulic pump shaft. Also, variations of the consumed electrical power by the grid cause a considerable load disturbance on the system. This thesis studies the hydraulic wind power transfer systems. To get a better understanding, a mathematical model of the system is developed and studied utilizing the governing equations for every single hydraulic component in the system. The mathematical model embodies nonlinearities which are inherited from the hydraulic components such as check valves, proportional valves, pressure relief valves, etc. An experimental prototype of the hydraulic wind power transfer systems is designed and implemented to study the dynamic behavior and operation of the system. The provided nonlinear mathematical model is then validated by experimental result from the prototype. Moreover, this thesis develops a control system for the hydraulic wind power transfer systems. To maintain a fixed frequency electrical voltage by the system, the generator should remain at a constant rotational speed. The fluctuating wind speed from the upstream, and the load variations from the downstream apply considerable disturbances on the system. A controller is designed and implemented to regulate the flow in the proportional valve and as a consequence the generator maintains its constant speed compensating for load and wind turbine disturbances. The control system is applied to the mathematical model as well as the experimental prototype by utilizing MATLAB/Simulink and dSPACE 1104 fast prototyping hardware and the results are compared.