Desenvolvimento de um modelo fuzzy para otimização da energia gerada por um sistema híbrido (solar-fotovoltaico e eólico)

Pós-graduação em Agronomia (Energia na Agricultura) - FCA

Método analítico para análise da estabilidade do gerador assíncrono através do monitoramento da tensão

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Desempenho de um sistema híbrido eólico-fotovoltaico de pequeno porte para energização rural

Pós-graduação em Agronomia (Energia na Agricultura) - FCA

Controladores fuzzy aplicados ao conversor de geradores de indução duplamente excitados em sistemas eólicos integrados a sistemas de potência

Este artigo apresenta novas estratégias de controle fuzzy aplicadas ao conversor estático interligado ao rotor dos geradores de indução duplamente excitados (DFIG), em esquemas eólicos de velocidade variável, integrados a redes elétricas reais. As estratégias de controle propostas são do tipo fuzzy "look-up-table" com supervisão. O desempenho de tais reguladores, baseados em inteligência computacional, é comparado com o obtido com controladores PI's a parâmetros fixos, na ocorrência de faltas no sistema elétrico de potência. Esses controladores fuzzy são destinados a garantir a continuidade da operação dos conversores, e melhorar o desempenho transitório do sistema, em relação aos controladores convencionais. Os resultados apresentados confirmam a eficácia das estratégias de controle adotadas. O modelo físico dos aerogeradores, consistindo de um grande número de turbinas eólicas, foi implementado através de uma ferramenta de simulação dinâmica, desenvolvida no ambiente computacional MATLABTM.

Desenvolvimento de monitoramento remoto em um sistema híbrido isolado de pequeno porte

Este trabalho visa avaliar as dificuldades e utilidades do monitoramento remoto de um sistema para o atendimento de cargas isoladas da rede elétrica, envolvendo sistemas reais em operação que podem ajudar a identificar os principais fatores que influenciam na vida útil desses dispositivos, tornando possível propor estratégias e tecnologias que melhorem a confiabilidade do sistema, possibilitem uma configuração mais adequada e reduzam os custos globais do sistema ao longo de sua vida útil. Para isso foi incorporado um sistema de monitoramento remoto via LabVIEW a um sistema híbrido isolado insta-lado em flutuante localizada as margens do lago da cidade de Tefé-AM. O sistema de geração foi composto inicialmente por um gerador fotovoltaico (FV) com potência de 2,08 kWp, dois subgeradores 1,04 kWp cada, e depois ampliado para 2,6 Wp mais 350 Wp de geração eólica. Além disso, um banco de acumuladores eletroquímicos com tensão nominal de 24 V e composto por 20 baterias de 150 Ah cada, Dois controladores de carga 24 V / 40 A e um inversor de onda senoidal de 1.500 VA. Resultados de operacionais apresentados neste trabalho ajudam a entender melhor o funcionamento desses sistemas e avaliar as barreiras encontradas no monitoramento remoto dessas unidades. Esse expe-rimento foi realizado em parceria do laboratório do Grupo de Estudos e Desenvolvimento de Alternativas Energéticas na Universidade Federal do Pará com o Núcleo de Inovação tecnológica do Instituto de Desenvolvimento Sustentável Mamirauá.

Estudio de un sistema de almacenamiento de energía eólica por medio de baterias

El objetivo de este trabajo consiste en evaluar los beneficios de la utilización de sistemas de almacenamiento de energía para incrementar el valor de un parque eólico. Debido a la naturaleza aleatoria inherente a la producción eléctrica de origen eólico, su integración en red plantea importantes problemas que suponen un reto tecnológico cada vez mayor a medida que la penetración de la energía eólica en el mix de generación aumenta. A su vez, las aplicaciones de los sistemas de almacenamiento de energía representan la oportunidad de mitigar los efectos indeseables de la producción eléctrica eólica. Los conocimientos adquiridos a lo largo de este proyecto se aplicarán para determinar qué sistema de almacenamiento de energía es óptimo para implantar en el parque eólico objeto del estudio, así como para cuantificar los beneficios derivados de la hibridación. ABSTRACT The aim of this work consist of assess the benefits of the use of energy storage systems for wind farm value enhacement. Due to the random nature inherent to wind electric generation, its grid integration carry important issues that represent a technology challenge that increases as wind generation penetration within energy mix increases as well. At the same time, energy storage systems applications represent an opportunity to mitigate the undesirable effects of wind generation. The knowledge gained throughout this project will be applied to determine which energy storage system is ideally suited for implementation within the wind farm under study, as well as quantify the benefits of hybridization.

Proteção de linhas de transmissão de sistemas VSC-HVDC utilizando limitadores de corrente de falta

Tecnologias HVDC que utilizam conversores do tipo fonte de tensão, o VSC-HVDC, ainda não são completamente difundidas e aplicadas no Brasil, em contraste com outros países que começaram a estudar e empregar este tipo de transmissão. Comparado com o HVDC tradicional, o VSC-HVDC é uma tecnologia de transmissão mais eficiente e pode superar deficiências encontradas na transmissão em corrente contínua convencional. O VSC-HVDC pode ser utilizado de maneira mais eficiente nas novas redes de energia, para alimentar ilhas, integração de geração eólica, renovação das linhas em centros urbanos, aplicações multiterminais e conexão com sistemas fracos. Por se tratar de uma tecnologia recente, o VSC-HVDC ainda não é amplamente adotado e uma das principais limitações da utilização destes sistemas é a sua fragilidade diante faltas na linha de corrente contínua. Neste contexto, limitadores de corrente de falta (LCF) podem ser utilizados para minimizar o impacto das faltas. A ação dos limitadores é benéfica ao sistema durante condições de falta, contudo, ainda assim é necessária a atuação do sistema de proteção para extinguir a condição faltosa. Portanto, este trabalho visa propor e avaliar um novo esquema de proteção que opere de maneira seletiva e confiável para sistemas VSC-HVDC na presença de LCF baseados em materiais supercondutores ou LCF indutivos. Para tanto, foram implementadas quatro funções de proteção tradicionais das linhas em CC, a saber: direcional de corrente, diferencial, sobrecorrente com restrição de tensão e ondas viajantes, e ainda, foi proposta uma nova função de proteção, a de condutância, a qual apresentou o menor tempo de identificação de falta, considerando as faltas mais severas. Adicionalmente, foi avaliado o comportamento destas funções quando o sistema apresenta os LCF em série com a linha. Foi demonstrado que é possível extrair os benefícios dos LCF sem deteriorar a qualidade dos resultados das funções de proteção, o que aumenta a segurança e confiabilidade dos sistemas VSC-HVDC, uma vez que os impactos das faltas são minimizados e as mesmas são identificadas em um curto intervalo de tempo.

Sistema de conversão de energia eólica baseado no gerador de indução duplamente alimentado: análise e contribuição ao controle da máquina

The humanity reached a time of unprecedented technological development. Science has achieved and continues to achieve technologies that allowed increasingly to understand the universe and the laws which govern it, and also try to coexist without destroying the planet we live on. One of the main challenges of the XXI century is to seek and increase new sources of clean energy, renewable and able to sustain our growth and lifestyle. It is the duty of every researcher engage and contribute in this race of energy. In this context, wind power presents itself as one of the great promises for the future of electricity generation . Despite being a bit older than other sources of renewable energy, wind power still presents a wide field for improvement. The development of new techniques for control of the generator along with the development of research laboratories specializing in wind generation are one of the key points to improve the performance, efficiency and reliability of the system. Appropriate control of back-to-back converter scheme allows wind turbines based on the doubly-fed induction generator to operate in the variable-speed mode, whose benefits include maximum power extraction, reactive power injection and mechanical stress reduction. The generator-side converter provides control of active and reactive power injected into the grid, whereas the grid-side converter provides control of the DC link voltage and bi-directional power flow. The conventional control structure uses PI controllers with feed-forward compensation of cross-coupling dq terms. This control technique is sensitive to model uncertainties and the compensation of dynamic dq terms results on a competing control strategy. Therefore, to overcome these problems, it is proposed in this thesis a robust internal model based state-feedback control structure in order to eliminate the cross-coupling terms and thereby improve the generator drive as well as its dynamic behavior during sudden changes in wind speed. It is compared the conventional control approach with the proposed control technique for DFIG wind turbine control under both steady and gust wind conditions. Moreover, it is also proposed in this thesis an wind turbine emulator, which was developed to recreate in laboratory a realistic condition and to submit the generator to several wind speed conditions.

System operational costs reduction with non-conventional reactive power sources

Wind energy installations are increasing in power systems worldwide and wind generation capacity tends to be located some distance from load centers. A conflict may arise at times of high wind generation when it becomes necessary to curtail wind energy in order to maintain conventional generators on-line for the provision of voltage control support at load centers. Using the island of Ireland as a case study and presenting commercially available reactive power support devices as possible solutions to the voltage control problems in urban areas, this paper explores the reduction in total generation costs resulting from the relaxation of the operational constraints requiring conventional generators to be kept on-line near load centers for reactive power support. The paper shows that by 2020 there will be possible savings of 87€m per annum and a reduction in wind curtailment of more than a percentage point if measures are taken to relax these constraints.

Controle de uma microrrede ilhada baseada em geração eólica-diesel com alto nível de inserção de geração eólica

The insertion of distributed generation units in the electric power systems have contributed to the popularization of microgrid concepts. With the microgrids, several potential benefits can be achieved in regard to power quality and supply reliability. However, several technical challenges related to the control and operation of microgrids, which are associated with high insertion of generation systems based on static converters, must be overcame. Among the opportunities in the context of microgrids, there is the islanded operation of microgrids temporarily disconnected from the electric power systems and also the autonomous operation of geographically isolated microgrids. The frequency in large power systems is traditionally controlled by the generation units based on traditional synchronous generator. The insertion of distributed generation units based on static power converters may bring difficulties to the frequency control in microgrids, due to the reduction of the equivalent inertia of conventional synchronous generators present in islanded and isolated microgrids. In this context, it becomes necessary the proposition of new operational and control strategies for microgrids control, taking into account the presence of distributed generation units based on full-rated converter. This paper proposes an operational and control strategy for the islanded operation of a winddiesel microgrid with high insertion level of wind generation. The microgrid adopted in this study comprises of a wind energy conversion system with synchronous generator based on full rated converter, a diesel generator (DIG) and a dump load. Due to the high insertion level of wind generation, the wind unit operates in Vf mode and the diesel generator operates in PQ mode. The diesel generator and the dump load are used to regulate the DC-link voltage of the wind generation unit. The proposed control allows the islanded operation of the microgrid only with wind generation, wind-only mode (WO), and with wind-diesel generation, wind-diesel mode (WD). For the wind-only mode, with 100% of penetration level of wind generation, it is proposed a DC-link voltage control loop based on the use of a DC dump load. For the winddiesel mode, it is proposed a DC-link voltage control loop added to the diesel generator, which is connected to the AC side of the microgrid, in coordinated action with the dump load. The proposed operational and control strategy does not require the use of batteries and aims to maximize the energy production from wind generation, ensuring the uninterrupted operation of the microgrid. The results have showed that the operational and control strategy allowed the stable operation of the islanded microgrid and that the DC-link voltage control loop added to the diesel generator and the dump load proved to be effective during the typical variations of wind speed and load.

Real-time load-side control of electric power systems

Two trends are emerging from modern electric power systems: the growth of renewable (e.g., solar and wind) generation, and the integration of information technologies and advanced power electronics. The former introduces large, rapid, and random fluctuations in power supply, demand, frequency, and voltage, which become a major challenge for real-time operation of power systems. The latter creates a tremendous number of controllable intelligent endpoints such as smart buildings and appliances, electric vehicles, energy storage devices, and power electronic devices that can sense, compute, communicate, and actuate. Most of these endpoints are distributed on the load side of power systems, in contrast to traditional control resources such as centralized bulk generators. This thesis focuses on controlling power systems in real time, using these load side resources. Specifically, it studies two problems.

(1) Distributed load-side frequency control: We establish a mathematical framework to design distributed frequency control algorithms for flexible electric loads. In this framework, we formulate a category of optimization problems, called optimal load control (OLC), to incorporate the goals of frequency control, such as balancing power supply and demand, restoring frequency to its nominal value, restoring inter-area power flows, etc., in a way that minimizes total disutility for the loads to participate in frequency control by deviating from their nominal power usage. By exploiting distributed algorithms to solve OLC and analyzing convergence of these algorithms, we design distributed load-side controllers and prove stability of closed-loop power systems governed by these controllers. This general framework is adapted and applied to different types of power systems described by different models, or to achieve different levels of control goals under different operation scenarios. We first consider a dynamically coherent power system which can be equivalently modeled with a single synchronous machine. We then extend our framework to a multi-machine power network, where we consider primary and secondary frequency controls, linear and nonlinear power flow models, and the interactions between generator dynamics and load control.

(2) Two-timescale voltage control: The voltage of a power distribution system must be maintained closely around its nominal value in real time, even in the presence of highly volatile power supply or demand. For this purpose, we jointly control two types of reactive power sources: a capacitor operating at a slow timescale, and a power electronic device, such as a smart inverter or a D-STATCOM, operating at a fast timescale. Their control actions are solved from optimal power flow problems at two timescales. Specifically, the slow-timescale problem is a chance-constrained optimization, which minimizes power loss and regulates the voltage at the current time instant while limiting the probability of future voltage violations due to stochastic changes in power supply or demand. This control framework forms the basis of an optimal sizing problem, which determines the installation capacities of the control devices by minimizing the sum of power loss and capital cost. We develop computationally efficient heuristics to solve the optimal sizing problem and implement real-time control. Numerical experiments show that the proposed sizing and control schemes significantly improve the reliability of voltage control with a moderate increase in cost.

Metocean Climate Impact on the Fatigue Assessment of a Jacket-Type Offshore Platform

When the offshore oil and gas supplies exhaust, most offshore platforms are decommissioned and removed. The purpose of this paper is to evaluate the fatigue damage that will occur during the service life of a jacket-type offshore platform using different fatigue approaches in particular locations. The locations considered for this metocean climate impact study were Norway (North Sea), Portugal (Atlantic Ocean - Leixões) and Italy (Adriatic Sea). A finite element model was created by the means of Sesam and two different fatigue analysis, deterministic and spectral, were applied. For the fatigue assessment, an appropriate description of the site-specific wave environment, during the jacket platform service life, must be accomplished. This description is usually provided by a wave scatter diagram. Wave scatter diagrams usually represent the long-term wave environment during a (typical) year and are based on several years of site-specific data to ensure that they adequately represent the wave environment at the location of the structure. In this thesis, the comparison between these fatigue approaches will serve as a pilot study for planned reliability analysis in decommissioned offshore platforms in order to maximize the reuse of these platforms for future wind generation systems.

Thunderstorms - their importance in wind engineering (a case for the next generation wind tunnel)

This paper attempts a state-of-the-art summary of research into thunderstorm wind fields from an engineering perspective. The characteristics of thunderstorms and the two extreme wind events-tornadoes and downbursts-spawn by thunderstorms are described. The significant differences from traditional boundary layer flows are highlighted. The importance of thunderstorm gusts in the worldwide database of extreme wind events is established. Physical simulations of tornadoes and downbursts are described and discussed leading to the recommendation that Wind Engineering needs to focus more resources on the fundamental issue - What is the flow structure in the strongest winds? © 2002 Published by Elsevier Science Ltd.

Using demand response to deal with unexpected low wind power generation in the context of smart grid

Demand response is assumed an essential resource to fully achieve the smart grids operating benefits, namely in the context of competitive markets. Some advantages of Demand Response (DR) programs and of smart grids can only be achieved through the implementation of Real Time Pricing (RTP). The integration of the expected increasing amounts of distributed energy resources, as well as new players, requires new approaches for the changing operation of power systems. The methodology proposed aims the minimization of the operation costs in a smart grid operated by a virtual power player. It is especially useful when actual and day ahead wind forecast differ significantly. When facing lower wind power generation than expected, RTP is used in order to minimize the impacts of such wind availability change. The proposed model application is here illustrated using the scenario of a special wind availability reduction day in the Portuguese power system (8th February 2012).

Adaptable control for electrical generation at irregural wind speeds

The main aims of this work are the development and the validation of one generic algorithm to provide the optimal control of small power wind generators. That means up to 40 kW and blades with fixed pitch angle. This algorithm allows the development of controllers to fetch the wind generators at the desired operational point in variable operating conditions. The problems posed by the variable wind intensity are solved using the proposed algorithm. This is done with no explicit measure of the wind velocity, and so no special equipment or anemometer is required to compute or measure the wind velocity.