Orientador: Luís Carlos Origa de Oliveira / Resumo: Na busca de soluções inovadoras para atender o aumento da demanda de consumo de energia elétrica, as fontes de energia de natureza fotovoltaica tem sido um dos principais pilares deste seguimento. São fontes intrinsicamente renováveis e o impacto sobre o meio ambiente resultante dos processos de produção de energia elétrica é praticamente desprezível, contribuindo de forma inequívoca para a sustentabilidade do planeta. Neste cenário, a expansão das aplicações de geradores fotovoltaicos é notável em praticamente todas as regiões industrializadas no mundo e, em alguns casos, já representa uma parcela significativa dos insumos energéticos de países desenvolvidos e em desenvolvimento. Apesar dos benefícios proporcionados pelo crescente uso desta tecnologia, em geral, as redes elétricas de distribuição de energia em operação, não foram planejadas para incorporar esta geração distribuída, em larga escala. Estudos recentes revelam que 10% de penetração de sistemas fotovoltaicos em relação a demanda da rede já pode causar impactos relevantes sobre o comportamento do sistema elétrico, sobretudo no tocante à regulação de tensão. Neste contexto, este trabalho tem por meta investigar as condições operacionais de redes de distribuição de energia, sob a influência de sistema fotovoltaico com relação aos impactos produzidos no perfil de tensão dos alimentadores. Assim, na perspectiva dos diferentes procedimentos convencionais utilizados para adequação dos níveis de tensão, discute-se a apli... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In the search for innovative solutions to meet the increasing demand for electricity consumption, photovoltaic energy sources have been one of the main pillars of this follow-up. They are intrinsically renewable sources and the impact on the environment resulting from the processes of electric power production is practically negligible, contributing unequivocally to the sustainability of the planet. In this scenario, the expansion of photovoltaic applications is notable in practically every industrialized region in the world, and in some cases already represents a significant share of the energy inputs of developed and developing countries. Despite the benefits provided by the growing use of this technology, in general, power distribution networks in operation were not planned to incorporate this distributed generation on a large scale. Recent studies show that 10% penetration of photovoltaic systems in relation to the demand of the grid can already have a significant impact on the behavior of the electrical system, especially in relation to voltage regulation. In this context, this work aims to investigate the operational conditions of power distribution networks under the influence of photovoltaic system in relation to the impacts produced on the voltage profile of the feeders. Thus, in the perspective of the different conventional procedures used to adjust the voltage levels, the applicability of some possible solutions is discussed, based on the R / X ratio behavior in th... (Complete abstract click electronic access below) / Mestre

The purpose of this thesis is to design and implement a linear quadratic optimal controller for a twin-buck converter with zero-voltage-transition (ZVT). The controller calculates duty ratio every cycle based on voltage and current feedback, as well as estimates the time instances when the synchronous rectification power switch current is zero. These time instances are crucial for ZVT operation. Via frequency modulation, the controller is designed to automatically regulate the output voltage to a desired value under load and voltage source variation. Simulations indicate that the proposed control design works. The controller is implemented using a Field Programmable Gate Array (FPGA). The experimental results match the simulations, which further verifies the applicability of the proposed voltage regulation strategy.

A Geração Distribuída no Brasil tem crescido ao longo dos anos, especialmente na fonte fotovoltaica e na categoria que a ANEEL denomina microgeração distribuída, que são centrais geradoras de energia elétrica com potência instalada menor ou igual a 75 kW e conectada na rede de distribuição por meio de instalações de unidades consumidoras. Apesar dos problemas tradicionais que podem ocorrer com a inserção em larga escala, como maiores perdas e desvios de tensão, as placas fotovoltaicas, conectadas à rede de distribuição por meio de um inversor, trazem a possibilidade de controlar a tensão no ponto de conexão, manipulando-se o fator de potência de saída do inversor, controlando a potência reativa. Neste contexto, considerando o uso dos inversores inteligentes com possibilidade de envio de sinal remotamente ao operador e a possibilidade de criação de Centros de Despacho de Geração Distribuída (CDGD), este trabalho tem por objetivo propor uma metodologia de regulação de tensão centralizada utilizando unidades de microgeração fotovoltaicas, em redes de distribuição com larga inserção. A metodologia proposta utiliza o conceito de despacho de potência reativa e fluxo de potência reativa ótimo, por meio de uma abordagem centralizada da rede, utilizando-se o software OpenDSS e MatLab, equipado com Algoritmo Genético (AG) para solucionar o problema de otimização. Para avaliar o desempenho do modelo, foram feitos estudos de caso no sistema IEEE 123 barras e em uma rede real em Alegrete. Os resultados obtidos validam a abordagem proposta, demonstra a aplicabilidade e limitações em casos reais. / The distributed generation in Brazil has increased in the past years, specially in photovoltaic power generation, at the category that Brazilian Electric Regulator ANEEL classifies as "distributed micro-generation", i.e., generation units in which the active power capacity is equal or bellow 75kW and conected on distribution network by the consumers. Despite the traditional problems that might occur due to high penetration of the units, e.g., higher losses and voltage sags and swells, they are conected to the network through an inverter that can be controlled in order to provide or consume reactive power, providing voltage regulation. In that context, considering the use of intelligent inverters that can be remotely operated by a centralized utility operator, this work aims to propose a centralized voltage regulation methodology using distributed micro-generation in distribution networks. The proposed methodology uses the concept of reactive power dispatch and optimal power flow, from a centralized view of the network, using the software MatLab and OpenDSS with Genetic Algorithm to solve the optimization problem. To evaluate the model, simulations were performed with the IEEE 123 bus system and with a real distribution network from the Alegrete city, in the Brazilian state of Rio Grande do Sul. The results show the proposed is valid, despite some limitations on real cases.

Today, conventional substation protection and control systems are of a widely distributed character. One substation can easily have as many as 50 data processing points that all perform similar algorithms on voltage and current data. There is also only limited communication between protection devices, and each device is only aware of the bay in which it is installed. With the intent of implementing a substation protection system that is simpler, more efficient and better suited for future challenges, Ellevio AB implemented a centralized system in a primary substation in 2015. It is comprised of five components that each handle one type of duty: Data processing, communication, voltage measurements, current measurements and breaker control. Since its implementation, the centralized system has been in parallel operation with the conventional, meaning that it performs station wide data acquisition, processing and communication, but is unable to trip the station breakers. The only active functionality of the centralized system is the voltage regulation. This work is an evaluation of the centralized system and studies its protection functionality, voltage regulation, fault response and output signal correlation with the conventional system. It was found that the centralized system required the implementation of a differential protection function and protection of the capacitor banks and busbar coupling to provide protection equivalent to that of the conventional system. The voltage regulation showed unsatisfactory long regulation time lengths, which could have been a result of low time resolution. The fault response and signal correlation were deemed satisfactory.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / This dissertation presents the study of a three-wire hibrid topology for voltage regulation for micro-hydroelectric generators that use self-excited induction in isolated operation. Initially, a literature review is presented in order to identify the main voltage regulation topologies applied to self-excited induction generators in the literature. From this review, a hybrid topology is proposed, which aims to regulate the voltage supplied by the generator to the isolated system. Thus, the mathematical modeling of the system is presented, comprising induction generator, the excitation capacitor, switched capacitor banks for voltage regulation, inductors filter and static reactive compensator. The following presents a control method based on reactive power control and design of switched capacitor banks using as reference the reactive power of the induction generator and static reactive compensator. The simulation and experimental results are presented to validate the proposed method. The use of the three-wire hybrid topology made of switched capacitor banks in conjunction with the static reactive compensator voltage regulation can be considered an addition to the scientific literature. / Nesta dissertação de Mestrado é apresentado o estudo de uma topologia híbrida a três fios, para a regulação de tensão em microcentrais hidrelétricas que utilizam geradores de indução auto-excitados em operação isolada. Inicialmente, é apresentada uma revisão bibliográfica, a fim de identificar as principais topologias de regulação de tensão aplicadas a geradores de indução auto-excitados presentes na literatura. A partir desta revisão, é proposta uma topologia híbrida, que tem por objetivo a regulação de tensão fornecida pelo gerador ao sistema isolado. Desta forma, é mostrada a modelagem matemática do sistema, composto por gerador de indução, capacitores de excitação, bancos de capacitores chaveados para regulação de tensão, indutores de filtro e compensador estático de reativos. A seguir, é apresentado um método de controle baseado no controle de potência reativa e o projeto dos bancos de capacitores chaveados tendo como referência a potência reativa do gerador de indução e do compensador estático de reativos. São apresentados também, os resultados de simulação e experimentais que validam o funcionamento do método proposto. O emprego da topologia híbrida a três fios formada por bancos de capacitores chaveados em conjunto com o compensador estático de reativos de regulação de tensão, pode ser considerado um acréscimo à literatura científica.

A Geração Distribuída no Brasil tem crescido ao longo dos anos, especialmente na fonte fotovoltaica e na categoria que a ANEEL denomina microgeração distribuída, que são centrais geradoras de energia elétrica com potência instalada menor ou igual a 75 kW e conectada na rede de distribuição por meio de instalações de unidades consumidoras. Apesar dos problemas tradicionais que podem ocorrer com a inserção em larga escala, como maiores perdas e desvios de tensão, as placas fotovoltaicas, conectadas à rede de distribuição por meio de um inversor, trazem a possibilidade de controlar a tensão no ponto de conexão, manipulando-se o fator de potência de saída do inversor, controlando a potência reativa. Neste contexto, considerando o uso dos inversores inteligentes com possibilidade de envio de sinal remotamente ao operador e a possibilidade de criação de Centros de Despacho de Geração Distribuída (CDGD), este trabalho tem por objetivo propor uma metodologia de regulação de tensão centralizada utilizando unidades de microgeração fotovoltaicas, em redes de distribuição com larga inserção. A metodologia proposta utiliza o conceito de despacho de potência reativa e fluxo de potência reativa ótimo, por meio de uma abordagem centralizada da rede, utilizando-se o software OpenDSS e MatLab, equipado com Algoritmo Genético (AG) para solucionar o problema de otimização. Para avaliar o desempenho do modelo, foram feitos estudos de caso no sistema IEEE 123 barras e em uma rede real em Alegrete. Os resultados obtidos validam a abordagem proposta, demonstra a aplicabilidade e limitações em casos reais. / The distributed generation in Brazil has increased in the past years, specially in photovoltaic power generation, at the category that Brazilian Electric Regulator ANEEL classifies as "distributed micro-generation", i.e., generation units in which the active power capacity is equal or bellow 75kW and conected on distribution network by the consumers. Despite the traditional problems that might occur due to high penetration of the units, e.g., higher losses and voltage sags and swells, they are conected to the network through an inverter that can be controlled in order to provide or consume reactive power, providing voltage regulation. In that context, considering the use of intelligent inverters that can be remotely operated by a centralized utility operator, this work aims to propose a centralized voltage regulation methodology using distributed micro-generation in distribution networks. The proposed methodology uses the concept of reactive power dispatch and optimal power flow, from a centralized view of the network, using the software MatLab and OpenDSS with Genetic Algorithm to solve the optimization problem. To evaluate the model, simulations were performed with the IEEE 123 bus system and with a real distribution network from the Alegrete city, in the Brazilian state of Rio Grande do Sul. The results show the proposed is valid, despite some limitations on real cases.

The future substation depends on finding a way to mitigate the effects of the drawbacks of the conventional legacy by employing the efficiency of the solid state switches in light of changing the loading features by time such as Electrical Vehicles (EV) and Photo-voltaic (PV) cells. In distribution transformers the ratio between the primary voltage and the secondary voltage cannot be changed, and the use of the on-load taps changers are limited. Poor voltage regulation and reactive power transmission is a direct reason for losses and shortening the life of several devices. This research discusses the considerations of applying Power Electronics (PE) approaches and designs that provide additional functions in regulating the voltage and controlling the reactive power that is injected in the distribution network, using embedded fractional rated converters attached partially with the windings of the LV transformer. These approaches studies the possible considerations that have the potentials to enhance the unit with more flexibility in controlling the voltage and reactive power at the last mile of the network, in order to decrease the losses and meet the future expectations for low voltage networks modifications, and that by using a Power Electronic (PE) approach has less losses and more functionality depending on the reliability of transformer and intelligence of PE solutions. The approach of a hybrid distribution transformer is introduced and its functionality in regulating the voltage and injecting reactive power is illustrated. A back-to-back converter is controlled according to the immediate need for voltage control and reactive power in Low Voltage (LV) networks, and for the purpose of controlling three unbalanced phases using two control strategies; resonant controller and vector control. The overall controller adds or decreases voltage (10%-20%) to/from the total output voltage in order to control the whole output voltage of the transformer. In addition, some loads need high amount of reactive power at last mile of the network, therefore the consideration of using switched capacitors technique is introduced to serve at the end user side whereby its ability to provide automatic variable reactive power compensation in a closed loop system is illustrated. The considerations results indicate significant potentials for deploying PE in the last mile of the network by using innovative designs and suitable control functions with less losses and costs.

This thesis is focused on voltage regulation in low voltage distribution system. It describes power management methods using photovoltaic inverters. The thesis describes the working PQ space of the inverter and the regulation characteristics of the active and reactive power in dependence on the voltage. The practical part focuses on the simulation of specific PQU control settings on the test models created in PSCAD. The model is used as a basis for real measurement. Outputs obtained from measurement and simulation are validated in the text. The last part of the thesis identifies limits for connecting resources with and without support.

Due to the rapid growth of grid-tied solar photovoltaic (PV) systems in the generation mix, the distribution grid will face complex operational challenges. High PV penetration can create overvoltages and voltage fluctuations in the network, which are major concerns for the grid operator. Traditional voltage control devices like switched capacitor banks or line voltage regulators can alleviate slow-moving fluctuations, but these devices need to operate more frequently than usual when PV generation fluctuates due to fast cloud movements. Such frequent operations will impact the life expectancy of these voltage control devices. Advanced PV inverter functionalities enable solar PV systems to provide reliable grid support through controlled real injection and/or reactive power compensation. This dissertation proposes a voltage regulation technique to mitigate probable impacts of high PV penetrations on the distribution voltage profile using smart inverter functionalities. A droop-based reactive power compensation method with active power curtailment is proposed, which uses the local voltage regulation at the inverter end. This technique is further augmented with very short-term PV generation forecasts. A hybrid forecasting algorithm is proposed here which is based on measurement-dependent dynamic modeling of PV systems using the Kalman Filter theory. Physical modeling of the PV system is utilized by this forecasting algorithm. Because of the rise in distributed PV systems, modeling of geographic dispersion is also addressed under PV system modeling. The proposed voltage regulation method is coordinated with existing voltage regulator operations to reduce required number of tap-change operations. Control settings of the voltage regulators are adjusted to achieve minimal number of tap-change operations within a predefined time window. Finally, integration of energy storage is studied to highlight the value of the proposed voltage regulation technique vis-à-vis increased solar energy use. / Ph. D. / Rapid growth of grid-tied solar photovoltaic (PV) systems poses both opportunities and technical challenges for the electric distribution grid. Significant among them are overvoltage and voltage fluctuations in the network, which may lead to overheating of electrical devices and equipment malfunction. Due to the variable nature of solar irradiance, existing voltage control devices often need to operate more frequently than usual which can cause recurring maintenance needs for these devices. To make solar PV more grid-friendly, changes are taking place in grid codes which encourage developing advanced PV inverter functions. With these functions, a smart inverter, which possesses bidirectional communication capability, can be integrated into a smart grid environment. This work discusses how these inverters can provide active power curtailment and reactive power compensation to maintain voltages at their points of interconnection. The inherent variability and uncertainty in solar energy production can be addressed with solar forecasting. Application of PV generation forecasting as a tool to aid distribution voltage control is proposed in this dissertation. Using solar forecasting, smart inverters can contribute in relieving the stress on other voltage control devices due to PV-induced fluctuations. Integrating storage elements can also aid this voltage regulation method, as they can consume surplus PV generation when needed. This dissertation is designed to provide a systematic approach to manage the overvoltage and voltage fluctuations on a real-time basis for a high PV penetration scenario. Proposed methodology combines smart inverter functionalities with solar forecasting and develops an application which can be realized to ensure seamless PV integration in a growing landscape of renewables.

Os objetivos deste trabalho compõem apresentar o andamento das pesquisas relacionadas à regulação de tensão em sistemas de distribuição de energia elétrica e propor um controle baseado em sistemas inteligentes para melhoria do perfil de tensão, permitindo que sejam atendidas as regulamentações mais exigentes do setor elétrico brasileiro. São considerados os aspectos sazonal, diário e não previsto do comportamento das cargas referentes à subestação de distribuição. Para isso, o trabalho propõe um relé regulador de tensão baseado em sistemas fuzzy que irá atuar diretamente no comutador de tap em transformadores de potência instalados em subestações de distribuição. Tal relé foi implementado por meio de um algoritmo computacional no Matlab. Os resultados foram obtidos por meio de simulações do real comportamento de carga indicando a viabilidade do sistema proposto. / The aim of this work is to present some research applied to voltage regulation in distribution systems and to propose a control system based on intelligent tools to improve the voltage profile of the system, considering the most demanding requirements of brazilian utilities. Periodical, daily and not foreseen aspects of the electrical loads in distribution system were considered. Therefore, the work proposes an automatic voltage regulator relay based on fuzzy systems, acting directly on load tap changing of transformers installed in a substation of the distribution system. This relay was implemented by computational algorithm in Matlab. The results were obtained by simulation of the real load behavior indicating the applicability of the proposed system.