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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
351

Suavização de potência da geração eólica utilizando lógica fuzzy e sistema de armazenamento de energia / Fuzzy logic and energy storage system for wind power smoothing

Carvalho, Wilhiam Cesar de 11 April 2019 (has links)
Dentre as diversas fontes de energia renovável que existem atualmente, a energia eólica é a que tem apresentado o maior crescimento nos Sistemas Elétricos de Potência (SEPs). A flutuação de potência da geração eólica, no entanto, tem causado grandes desafios no que diz respeito à Qualidade da Energia Elétrica (QEE) e à operação do SEP. O grande progresso dos Sistemas de Armazenamento de Energia (SAEs), aliado à crescente inserção de geração eólica nos SEPs, tem promovido grande interesse na utilização dos SAEs junto aos aerogeradores. Este trabalho apresenta a utilização de um SAE, conectado ao elo CC do conversor back-to-back do aerogerador, e uma técnica de controle baseada na lógica fuzzy para suavizar as variações da potência de curto prazo da geração eólica. A técnica de controle proposta também é utilizada para gerenciar o Estado de Carga (SOC) do SAE para evitar a condição sobrecarregada e totalmente descarregada. O controle fuzzy é testado e comparado com uma técnica de controle convencional e também com a topologia típica do aerogerador, onde não é utilizado o SAE. As técnicas são avaliadas e comparadas com base em diferentes indicadores numéricos da qualidade da suavização. Um simulador digital em tempo real (RTDSR) é utilizado para realizar as simulações, onde é considerado um aerogerador de 2 MW, um supercapacitor e uma microrrede baseada no benchmark do CIGRÉ de média tensão. Os resultados mostraram que as técnicas de controle do supercapacitor possibilitaram uma adequada suavização de potência da geração eólica e puderam contribuir para a QEE e a operação da microrrede. A técnica inteligente baseada no controlador fuzzy mostrou resultados superiores à técnica convencional e, portanto, apresentou grande potencial para a aplicação. / Among several renewable energy sources existing nowadays, wind energy has presented the largest growth in power systems. The wind power fluctuations, however, has brought great challenges concerning Power Quality (PQ) and power system operation. The great progress of Energy Storage Systems (ESSs), together with the increasing penetration of wind power worldwide, has lead to a great interest in the use of ESS in wind energy. This study presents the application of a ESS, connected to the DC link of the backto- back converter of the wind turbine, and a control technique based on fuzzy logic to smooth out the short-term wind power fluctuations. The proposed control technique is also used to manage the State of Charge (SOC) of the ESS to avoid the overcharged and undercharged states. The fuzzy control is tested and compared with a conventional control technique and also with the typical wind turbine topology, where the ESS is not used. The techniques are evaluated and compared based on different quantitative indicators that represent the quality of the power smoothing. Simulations are carried out in the Real-Time Digital Simulator (RTDSR), where a 2 MW wind turbine, a supercapacitor and a microgrid system based on the CIGRÉ medium voltage benchmark are considered. The results have shown that the control techniques of the supercapacitor permitted a suitable smoothing of the fluctuating wind power and contributed to the microgrid PQ and operation. The intelligent control technique based on the fuzzy logic has shown superior performance compared to the conventional technique and, therefore, presented great potential for application.
352

Avaliação da estabilidade de aerogeradores via método direto / Stability assessment of wind turbines via direct method

Sohn, Alexandre Prodossimo 23 April 2019 (has links)
Esta tese trata de dar um passo na direção de revisar o problema de estabilidade transitória e a teoria do método PEBS para incluir em seus fundamentos modelos de fontes alternativas e seus limites operacionais. A conceituação do método direto com restrição é estabelecida via teoria de sistemas dinâmicos restritos e do conceito de região de estabilidade restrita. Particularmente, avalia-se a estabilidade de velocidade das principais configurações de aerogeradores equipados com gerador de indução, considerando como requisito operacional a curva de suportabilidade a afundamentos de tensão, ou curva LVRT. Um sistema dinâmico auxiliar aumentado é desenvolvido para representar a curva LVRT, que é um requisito dependente do tempo, por meio de uma restrição invariante no tempo descrita em termos de uma variável de estado auxiliar. Este sistema auxiliar tem sua região de estabilidade irrestrita igual à região de estabilidade restrita do sistema dinâmico restrito. Os modelos são apresentados na forma de equações algébricas e diferenciais. O problema de estabilidade de velocidade e o problema de violação de limites de tensão são investigados via análises da região de estabilidade do ponto de equilíbrio estável do sistema pós-falta e dos tempos críticos de abertura obtidos para várias perturbações. Os resultados mostram que: i) para distintos limites operacionais e para distintos parâmetros da máquina de indução, as regiões de estabilidade para um dado ponto de equilíbrio podem ser significativamente diferentes, ii) na maioria dos casos analisados, os limites de tensão são violados antes dos aerogeradores perderem a estabilidade de velocidade, o que mostra como é importante considerar limites operacionais nas avaliações de estabilidade via método direto para evitar que o sistema elétrico de potência fique vulnerável e iii) as funções energia desenvolvidas, tanto para avaliar o problema de estabilidade de velocidade, como para avaliar o problema de violação de limites de tensão, são em geral capazes de realizar boas estimativas dos tempos críticos de abertura. Os estudos elaborados nesta tese sobre a avaliação da estabilidade de aerogeradores via método direto, contribuem com aplicações inéditas que podem ser utilizadas nas análises de segurança em tempo real de sistemas elétricos de potência que contemplem fontes alternativas e seus limites operacionais. / This thesis gives a step forward in the direction of reviewing the problem of transient stability and the theory of PEBS method to include models of renewable power plants and their operational limits. The formulation of direct methods with constraint is accomplished by exploring the theory of constrained dynamic systems and the concept of constrained stability region. In particular, the speed stability of the main wind turbine configurations equipped with an induction generator is analyzed, considering the low voltage ride-through requirement, or LVRT curve, as a constraint to the model. An augmented auxiliary dynamical system is developed to represent the time-dependent LVRT constraint as an equivalent time invariant constraint written in terms of an auxiliary state variable. This auxiliary system has its unconstrained stability region equals to the constrained stability region of the constrained dynamic system. The models are described in the form of algebraic and differential equations. The problem of speed stability and the problem of disconnection of wind turbines due to voltage limits violation are investigated via analysis of stability region of the post-fault equilibrium point and critical clearing times obtained for several perturbations. The results show that: i) for different operational limits and for different parameters of the induction machine, the stability regions for a given operating point can be significantly different, ii) in most cases, the violation of the LVRT curve occurs before the speed instability, which reveals the importance of include operational limits in transient stability analysis and in the formulation of direct methods and iii) in most cases, the developed energy functions to evaluate the problem of speed stability and the problem of voltage limits violation, are generally capable of making good estimates of critical clearing times. The developed studies about the transient stability assessment of different models of wind turbines via direct method contribute with applications that can be used in real-time security assessments of power systems that contemplate renewable power plants and their operational limits.
353

Control and Model Identification on Renewable Energy Systems / Commande et identification de modèles pour des systèmes d’énergie renouvelables

Jaramillo López, Fernando 26 September 2014 (has links)
La situation compromettante de l'environnement due à la pollution, et les coûts élevés des combustibles fossiles ont engagé des nouvelles politiques et réglementations et ont fortement incité l’augmentation de l’utilisation de nouvelles sources d'énergie renouvelables. De nombreux pays dans le monde ont augmenté de façon importante le développement de ces sources d'énergie. Deux des systèmes d'énergies renouvelables les plus couramment utilisés sont les systèmes éoliens (SE) et les systèmes photovoltaïques (SP). SE convertissent l'énergie du vent en énergie électrique au moyen d'un processus électromécanique et SP convertissent directement l'énergie solaire en énergie électrique au moyen d'un processus semi-conducteur. Ces systèmes présentent de nombreux défis qui doivent être résolus afin de gagner du terrain sur les systèmes d'énergies traditionnelles. L'un de ces défis est d'augmenter l'efficacité du système avec la commande des éléments de puissance. Afin d'atteindre cet objectif, il est nécessaire de mieux comprendre le comportement dynamique de ces systèmes et de développer des nouveaux modèles mathématiques et des nouvelles techniques de commande. Ces techniques nécessitent souvent des informations du système qui ne sont pas disponibles --- ou sont trop chères si on devait les mesurer. Pour résoudre ce problème, il est nécessaire de créer des algorithmes qui puissent estimer cette information, cependant, ce n'est pas une tâche facile, car les signaux des sources d'énergie dans SE et SP (c.-à-d. la vitesse du vent, rayonnement solaire, température) entrent dans les modèles mathématiques par une relation non linéaire. Ces algorithmes doivent pouvoir estimer ces signaux --- ou les signaux qui dépendent d’eux--- avec une bonne précision. Aussi, il est nécessaire de concevoir des lois de commande qui opèrent les systèmes à leur point maximum de puissance. Dans ce travail, nous proposons des nouveaux algorithmes d'estimation et des lois de commande qui sont liés à l'augmentation de l'efficacité énergétique dans SE et SP. Des travaux antérieurs liés à l'estimation des signaux mentionnés, les considéraient comme constants. Dans cette thèse, les algorithmes d'estimation proposés considèrent l'état variable des ces signaux. Dans toutes ces nouvelles propositions, la stabilité asymptotique est prouvée en utilisant les théories de Lyapunov. Les lois de commande sont calculées en utilisant les modèles non linéaires des systèmes. En outre, certaines des ces solutions sont étendues au cas général, qui peut être utilisé sur une large classe des systèmes non linéaires. Le premier, est un estimateur de paramètres pour les systèmes non linéaires. Il permet d'estimer les paramètres non linéaires variant dans le temps. La deuxième proposition est la conception d’un schéma pour une classe de systèmes non linéaires adaptatifs qui permet de compenser les incertitudes et les perturbations qui satisfont à la "condition de correspondance". / The compromising situation of the environment due to pollution, and the high costs of the fossil fuels have originated new policies and regulations that have stimulating the interest on alternative energy sources. Many countries around the world have increased in an important way the penetration of these energy sources. Two of the most widely used renewable energy systems are the wind turbines systems (WTS) and the photovoltaic systems (PVS). WTS convert wind energy in electric energy by means of an electromechanical process and PVS convert solar energy directly in electric energy by means of a semiconductive process. These systems show many challenges that need to be solved in order to gain ground to the traditional energy systems. One of these challenges is increase the overall system efficiency by controlling the power conditioning elements. In order to achieve this, is necessary to better understand the dynamic behavior of these systems and develop new mathematical models and new control techniques. These techniques often require system information that is not possible ---or is too expensive--- measure. In order to solve this problem, is necessary to create algorithms that are able to estimate this information, however, this is not an easy task, because the signals of the energy sources in WTS and PVS (i.e., wind speed, irradiance, temperature) enter in the mathematical models in a nonlinear relation. These algorithms have to be able to estimate these signals ---or the signals that depend on them--- with good precision. Also, it is necessary to design control laws that operate the systems at their maximum power point. In this work, we propose novel estimation algorithms and control laws that are related with the increase of the energetic efficiency in WTS and PVS. Previous works related with estimation of the mentioned signals considered them as constants. In this thesis, the proposed estimation algorithms consider the time-varying condition of these signals. In all of these novel propositions, uniform asymptotic stability is proved using Lyapunov theories. The control laws are derived using the overall nonlinear models of the systems. In addition, some of these solutions are extended to the general case, which can be used on a large-class of nonlinear systems. The first one, is a novel parameter estimator for nonlinear systems. It allows to estimate time-varying nonlinear parameters. The second general proposition is a framework for a class of adaptive nonlinear systems that allows to compensate for uncertainties and perturbations that satisfy the matching condition.
354

Estudo do fluxo de potência de um gerador de indução de dupla alimentação atuando em um sistema de geração eólio-elétrica / Study of variation of power flow of a doubly-fed induction generator acting on a wind power generation system

Jacob, Natália Moreira 03 April 2013 (has links)
A captação de energia eólica tem sido alvo de estudos em todo o mundo nas últimas décadas devido aos incentivos pela busca por geração de energia por meio de fontes alternativas. A configuração mais utilizada atualmente são as turbinas de três pás com eixo horizontal, upwind, operando com velocidade variável com limitação de potência por variação de passo, e utilizando o gerador de indução de dupla alimentação. A operação em velocidade variável com atuação no ângulo de passo permite a máxima captação de energia para as diferentes velocidades de vento, enquanto evita que a turbina ultrapasse o seu valor nominal de potência. O uso de conversores permite o controle das correntes do rotor, variando sua velocidade, e o controle da potência reativa de estator, e a montagem do tipo back-to-back permite que o fluxo de energia do rotor flua para a rede ou da rede. A modelagem matemática do sistema foi toda referenciada no referencial síncrono com notação vetorial e orientação de fluxo de rede, simplificando os modelos matemáticos. Para a montagem dos controladores foi utilizado o método de Controle de Modelo Interno e de Resistência Ativa. A montagem de todo o sistema para simulação foi realizada no Matlab/Simulink, e seu desenvolvimento é mostrado no decorrer do trabalho. Este trabalho analisa o fluxo de energia do sistema, desde a energia captada pelo vento até a energia entregue à rede. Para isso, são feitas análise dos fluxos das potências ativa e reativa do sistema, para fator de potência unitário, indutivo e capacitivo e para os mais recorrentes comportamentos do vento. Também são feitas análises a respeito dos regimes de operação do sistema, definidos a partir da relação entre os fluxos de potência, concluindo que a máquina poderá operar como gerador ou motor, devido principalmente à intensidade da variação do vento. / The use of wind energy has been the subject of studies around the world in recent decades due to the incentives to search for power generation through alternative sources. The most widely used configuration has been the three blades with horizontal axis and upwind turbine, operating in variable speed with power limitation by varying the pitch angle, and using the doubly fed induction generator configuration. The variable speed operation with power limitation enable for maximum energy harvesting for different wind speeds and prevents the turbine exceeds its nominal power. The use of converters allows for control of the rotor currents, varying the speed, and stator reactive power, and assembling type back-to-back allows for the rotor energy flux to flow into and out of the grid. Mathematical modeling of the whole system was referenced in the synchronous reference frame with vector notation and oriented by the grid flux, simplifying the mathematical models. For installation of the drivers, were used the Internal Model Control and Active Damping methods. The assembly of the entire system for simulation was conducted on Matlab / Simulink, and its step to step is shown in this work. This study analyzes the energy flow of the system, from the energy harvest from de wind to the energy delivered to the grid. To reach this, flow analysis of active and reactive power of the system is done, using unity, inductive and capacitive power factor, for the most recurrent wind behaviors. Analysis are made about the operation regimes of the system, defined as the relationship between the power flows, concluding that the machine can operate as a generator or motor, mainly due to the variation of the wind intensity.
355

Advances in foundation design and assessment for strategic renewable energy

Dallyn, Paul A. January 2017 (has links)
In order to meet EU legislation on emissions, significant effort is being invested into the development of cost-effective renewable power generation technologies. The two leading technologies are solar and wind power because of their potential for the lowest levelised cost of energy and for showing a growth in installed capacity and technological development. Various research findings have suggested that significant cost savings in the capital expenditure of renewable energy projects can be made through the optimisation of their support foundations, the understanding of which has formed the main goal of the research.
356

Análise dos limites máximos de inserção de geração eólica em redes de distribuição conforme a variação de tensão de regime permanente / Maximum integration levels of wind power in distribution grids according to steady state voltage variation requerements

Löwenberg, Vanessa Viquetti 12 April 2013 (has links)
Made available in DSpace on 2017-07-10T17:11:45Z (GMT). No. of bitstreams: 1 DISSERTACAO VANESSAVIQUETTI LOWENBERG.pdf: 2250957 bytes, checksum: 81895e5a2a510f6aea4627b4b6c0d230 (MD5) Previous issue date: 2013-04-12 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This work considers the connection of wind power units to the distribution system, aiming at verifying the maximum power limits that can be connected complying with given connection requirements. The maximum power limits have been characterized in terms of maximum integration levels, to the equivalent capacity in the connection node, and in terms of maximum penetration levels, to the full load power feeder. The steady-state voltage in the distribution system nodes has to comply with a priori given maximum variation limits for all possible wind farm working conditions, supplying from 20 to 100% of its nominal power. The research has been developed in two different distribution feeders: a 5-nodes distribution feeder, connecting the wind farm at four different points and considering three different load levels; a 32-nodes distribution feeder, connecting the wind farm to ten different nodes of the system and also considering three different load levels. The maximum integration and penetration levels of wind power have been evaluated in terms of (i) the connection node characteristics (equivalent X/R ratio impedance and voltage); (ii) the feeder load; (iii) the connection node. The connection of either one or two wind farms has been considered for both feeders, assuming wind farms with equal characteristics. The analysis showed strong influence of the impedance X/R ratio on the maximum wind energy integration and penetration levels. The feeder load influences these levels in a non-linear manner and in some cases also an in inverse way, i.e. the load increasing can either increase or decrease the maximum integration level. The equivalent voltage influence on the maximum wind power integration and penetration was not evident in the performed tests. The feeder structure did influence the levels since, in many cases, the maximum integration and penetration levels of wind power have not been determined by the voltage in the connection node but by the voltage in other feeder s node. In general, the connection of two wind farms showed higher wind energy penetration levels compared to only one wind farm, being more or less expressive according to the connecting node characteristics. / Este trabalho se insere no contexto do estudo da conexão de unidades de geração eólica em sistemas de distribuição no sentido de verificar quais os limites máximos de potência que po- dem ser interligados atendendo a determinados requisitos de conexão. Os limites máximos de potência são caracterizados em termos dos níveis máximos de inserção de geração eólica, relativos à capacidade equivalente vista pelo nó de conexão, e da máxima penetração de geração eólica, relativos à carga instalada no alimentador. Exige-se que a tensão de regime permanente nos nós do alimentador de distribuição atenda a limites máximos pré-estabelecidos de variação para todas as condições operativas possíveis do parque eólico produzindo desde 20% até 100% de sua potência nominal. O estudo foi realizado através de simulação computacional sobre dois alimentadores de distribuição diferentes: um alimentador com 5 nós, conectando o parque eólico em quatro diferentes pontos deste sistema e considerando três níveis diferentes de carregamento; e um alimentador com 32 nós, conectando o parque eólico em dez diferentes pontos deste sistema e considerando também três níveis diferentes de carregamento. Os níveis máximos de inserção e penetração de geração eólica foram analisados em função: (i) das características do nó de conexão (relação X/R da impedância e tensão equivalentes); (ii) do carregamento do alimentador; (iii) do nó de conexão. Para os dois alimentadores foram considerados os casos da conexão de um e de dois parques eólicos, sendo que em todos os casos foram adotados parques eólicos idênticos. As análises realizadas mostraram grande influência da relação X/R da impedância equivalente tanto sobre a inserção quanto a penetração de geração eólica. O carregamento do alimentador influenciou de maneira não linear e também em alguns casos de maneira inversa, significando que o aumento do carregamento pode tanto aumentar quanto reduzir a máxima inserção de geração eólica. A influência da tensão equivalente sobre a inserção e penetração de geração eólica não mostrou-se muito evidente nos testes realizados. A topologia do alimentador teve influência, pois em diversos casos os limites má- ximos de inserção e penetração de geração eólica foram determinados pela tensão em nós do alimentador distintos do nó de conexão do parque. De maneira geral, a conexão de dois parques eólicos mostrou atingir níveis superiores de penetração de geração eólica em comparação a um só parque, podendo ser mais ou menos expressiva conforme a característica dos nós de conexão envolvidos.
357

Étude expérimentale et numérique du décrochage dynamique sur une éolienne à axe vertical de forte solidité / Experimental and numerical study of dynamic stall on a high solidity vertical axiswind turbine

Beaudet, Laurent 10 July 2014 (has links)
L'éolienne Darrieus connaît un intérêt accru ces dernières années parce qu'elle représente une solution alternative potentielle de production d'électricité dans les milieux urbains. En particulier,une éolienne de forte solidité peut être choisie car certaines de ses propriétés peuvent être avantageuses pour son implantation proche de zones habitées. A l'inverse, certaines difficultés aérodynamiques émergent. Ce type d'éolienne fonctionne à de faibles vitesses réduites pour lesquelles le décrochage dynamique a un rôle très significatif. L'objectif de ce travail de thèse consiste à compléter la connaissance du phénomène de décrochage dynamique sur une éolienne à axe vertical afin d'améliorer les modèles numériques de prédiction existants. Cette étude s'appuie sur une analyse combinée de résultats numériques et expérimentaux. Les simulations numériques sont produites avec une méthode des panneaux bidimensionnelle instationnaire. Les effets de la viscosité sont introduits par des corrections utilisant notamment un modèle semi-empirique de décrochage dynamique. Le travail expérimental s'est concentrée sur la dynamique tourbillonnaire à proximité immédiate du rotor résultante du décrochage dynamique. Le montage se compose d'une éolienne à pale droite placée dans une soufflerie. Des mesures instationnaires de la répartition de pression pariétale le long de la corde et des mesures de champ de vitesse par vélocimétrie par images de particules ont été accomplies. Les résultats révèlent la manière dont les caractéristiques du décrochage dynamique sont conditionnées par la vitesse réduite. Le retard au décrochage, l'intensité de l'effet du tourbillon de décrochage dynamique et sa convection ont été quantifiés. Enfin, un examen critique de l'applicabilité du modèle de Leishman-Beddoes pour simuler efficacement les effets du décrochage dynamique a été réalisé. / The Darrieus wind turbine has entered a period of renewed interest over the last years because it may stand for an alternative solution to produce electricity in urban areas. In particular, high solidity wind turbine can be chosen to take benefit from some of its key properties for use near populated city areas. Conversely, some aerodynamic problems arise. This type of wind turbine operates at low tip speed ratio for which dynamic stall has a very significant role. The goal of this work is to provide valuable data to complement the knowledge of the dynamic stall phenomenon that occurs on a vertical axis wind turbine in order to improve existing numerical models. This study relies on a combined analysis of numerical and experimental results. The numerical simulations are based on a bidimensional unsteady vortex panel method. Effects of viscosity are introduced by adding corrections computed with a semi-empirical dynamic stall model. The experimental work focuses on the dynamics of the shed vortices existing in the vicinity of the rotor as a result of dynamic stall. The set-up consists of a straight-bladed wind turbine tested in a wind tunnel. Unsteady pressure distribution measurements along the chord and velocity fields measurements by particle image velocimetry were carried out. Results indicate how the characteristics of dynamic stall are conditioned by the tip speed ratio. Stall inception delay, magnitude of the dynamic stall vortex effects and its convection velocity were evaluated. Blade/Vortex interaction was analyzed through the observation of the vortical system downstream of the rotor. In addition, a critical review of the suitability of the Leishman-Beddoes model to effectively simulate the effects of dynamic stall was accomplished.
358

Design of wind turbine tower and foundation systems: optimization approach

Nicholson, John Corbett 01 May 2011 (has links)
A renewed commitment in the United States and abroad to electricity from renewable resources, such as wind, along with the recent deployment of very large turbines that rise to new heights, makes obtaining the most efficient and safe designs of the structures that support them ever more important. Towards this goal, the present research seeks to understand how optimization concepts and Microsoft Excel's optimization capabilities can be used in the design of wind turbine towers and foundations. Additionally, this research expands on the work of previous researchers to study how considering the tower and foundation as an integral system, where tower support conditions are not perfectly rigid, affects the optimal design. Specifically, optimization problems are formulated and solved with and without taking into account the effect of deflections, resulting from the foundation's rotational and horizontal stiffness, on natural frequency calculations. The general methodology used to transcribe the design of wind turbine towers and foundations into an optimization problem includes: 1) collecting information on design requirements and parameter values 2) deciding how to analyze the structure 3) formulating the optimization problem 4) implementation using Microsoft Excel. Key assumptions include: 1) use of an equivalent lumped mass method for estimating natural frequency 2) International Electrotechnical Commission (IEC) 61400-1 extreme loading condition controls design (i.e. fatigue loading condition is not considered) 3) extreme loads are obtained from manufacturer provided structural load document that satisfies loading cases outlined in IEC 61400-1 4) wind forces on the tower are calculated in accordance with IEC 61400-1 5) optimization variables are continuous. The sum of the tower material and fabrication cost and the total foundation cost is taken as the objective function. Important conclusions from this work include: 1) optimization concepts and Microsoft Excel's optimization capabilities can be used to obtain reasonable conceptual level designs and cost estimates 2) detailed designs and cost estimates could be achieved using a solver capable of handling discrete optimization problems 3) considering the tower and foundation as an integral system results in a more expensive, but safer, design 4) for the assumed parameter values, the constraint on the tower's natural frequency was found to control the tower design and the bearing capacity constraint was found to control the foundation design 5) relaxing or tightening the limit on the natural frequency will result in the greatest benefit or penalty, respectively, on the optimum solution.
359

DESIGN AND TESTING OF A WIND ENERGY HARNESSING SYSTEM FOR FORCED CONVECTIVE DRYING OF GRAIN IN LOW WIND SPEED, WARM AND HUMID CLIMATES

Agbali, Francis Akumabi 01 January 2019 (has links)
Forced convective drying using a wind turbine mechanically connected to a ventilation fan was hypothesized for low cost and rapid grain drying in developing countries. The idea was tested using an expandable wind turbine blade system with variable pitch, at low wind speeds in a wind tunnel. The design was based on empirical and theoretical models embedded in a graphical user interface (GUI) created to estimate airflow-power requirements for drying ear corn. Output airflow (0.0016 - 0.0052 m3kg-1s-1) increased within the study wind speed range (2.0 - 5.5 m/s). System efficiency peak (8.6%) was observed at 3.5 m/s wind speed. Flow resistance was overcome up to 1m fill depth in 0.5 m x 0.5 m wide drying bin. Drying study at different airflow rates (no forced convection, 0.002 m3kg-1s-1 and 0.008 m3kg-1s-1) were conducted in a controlled environment at 35oC and 45% relative humidity with mean drying time; 40.3, 37.9 and 22.9 h respectively, that reduced with increasing airflow while drying the ear corn from 22% to 15% moisture content. The overall result supports the hypothesis that the wind convection system increased grain drying rates and should be further developed.
360

Development of a pitch based wake optimisation control strategy to improve total farm power production

Tan, Jun Liang January 2016 (has links)
In this thesis, the effect of pitch based optimisation was explored for a 80 turbine wind farm. Using a modified Jensen wake model and the Particle Swarm Optimisation (PSO) model, a pitch optimisation strategy was created for the dominant turbulence and atmospheric condition for the wind farm. As the wake model was based on the FLORIS model developed by P.M.O Gebraad et. al., the wake and power model was compared with the FLORIS model and a -0.090% difference was found. To determine the dynamic predictive capability of the wake model, measurement values across a 10 minute period for a 19 wind turbine array were used and the wake model under predicted the power production by 17.55%. Despite its poor dynamic predictive capability, the wake model was shown to accurately match the AEP production of the wind farm when compared to a CFD simulation done in FarmFlow and only gave a 3.10% over-prediction. When the optimisation model was applied with 150 iterations and particles, the AEP production of the wind farm increased by 0.1052%, proving that the pitch optimisation method works for the examined wind farm. When the iterations and particles used for the optimisation was increased to 250, the power improvement between optimised results improved by 0.1144% at a 222.5% increase in computational time, suggesting that the solution has yet to fully converge. While the solutions did not fully converge, they converged sufficiently and an increase in iterations gave diminishing results. From the results, the pitch optimisation model was found to give a significant increase in power production, especially in wake intensive wind directions. However, the dynamic predictive capabilities will have be improved upon before the control strategy can be applied to an operational wind farm.

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