Wind energy industry thrived in the last three decades, environmental concerns and government regulations stimulate studies on wind farm location selection and wind turbine design. Full-scale experiments and high-fidelity simulations are restrictive due to the prohibitively high cost, while the model-scale experiments and low-fidelity calculations miss key flow physics of unsteady high Reynolds number flows. A hybrid RANS/LES turbulence model integrated with transition formulation is developed and tested by a surrogate model problem through joint experimental and computational fluid dynamics approaches. The model problem consists of a circular cylinder for generating coherent unsteadiness and a downstream airfoil in the cylinder wake. The cylinder flow is subcritical, with a Reynolds number of 64,000 based upon the cylinder diameter. The quantitative dynamics of vortex shedding and Reynolds stresses in the cylinder near wake were well captured, owing to the turbulence-resolving large eddy simulation method that was invoked in the wake. The power spectrum density of velocity components showed that the flow fluctuations were well-maintained in cylinder wake towards airfoil and the hybrid model switched between RANS/LES mode outside boundary layer as expected. According to the experimental and simulation results, the airfoil encountered local flow angle variations up to ±50 degrees, and the turbulent airfoil boundary layer remained attached. Inspecting the boundary layer profiles over one shedding cycle, the oscillation about mean profile resembled the Stokes layer with zero mean. Further processing the data through phase-averaging technique found phase lags along the chordwise locations and both the phase-averaged and mean profiles collapsed into the Law of Wall in the range of 0 < y+ < 50. The features of high blade loading fluctuations due to unsteadiness and transitional boundary layers are of interest in the aerodynamic studies of full-scale wind turbine blades, making the model problem a comprehensive benchmark case for future model development and validation. / Ph. D. / Wind energy industry thrived in the last three decades, environmental concerns and government regulations stimulate studies on wind farm location selection and wind turbine design. Full-scale experiments and high-fidelity simulations are restrictive due to the prohibitively high cost, while the model-scale experiments and low-fidelity calculations miss key flow physics of of the full-scale models. The current study adopted a joint experimental and computational fluid dynamic approach to design a surrogate problem that features the unsteady flow physics presented in the full-scale wind turbine blades. A new hybrid turbulence model was implemented and validated against the complementary experimental results. The new model improves the accuracy of the current industry-standard turbulence models without excessive computational cost, making it a viable solution to the high-fidelity full-scale simulations in the future.

The development of the wind energy exploitation is a sum of processes which are subject to variety of heterogeneous factors. The nature and the leverage power of those factors vary and develop over time. Each regional or national location can be characterized by variety of factors, which are specific for respective locations. The wind energy development in the Czech Republic is influenced by number of barriers which restrain or slow down further progress. These barriers stem from environmental, economical, social and institutional disposition/nature of respective technologies. This thesis at first, based on available qualitative and quantitative data, describes and analyzes the situation and development of the wind energy exploitation. Specifics of the wind energy are placed in the context of selected European countries where factors and barriers influencing the development is described. The theme is regarded with spatio-temporal distribution of a "new technology". The thesis goes on focusing on identification of barriers that have impact on the wind energy development in the Czech Republic. Those restrictions/barriers are subsequently confronted with stands and perception of specific stakeholders, which are involved in the process. Analyses are carried out not only on individual barriers but also...

The Complimentary Energy Decision Support Tool (CEDST) was conceived to be a renewable energy calculator designed specifically for rural sites and agricultural operations in Ontario, though could easily assess urban sites as well, and equipped with the ability to compare the feasibility of different technologies. The Wind Energy Calculator (WEC) component of the CEDST project was the focus of this thesis and was developed since research revealed no current wind prediction tools that met CEDST needs. Verification of WEC predictions found prediction accuracy to have bounds of +/- 60% on actual turbine energy production and was equivalent to the actual generation for 21% of cases. The discrepancy could have resulted from unusual annual wind speeds, which had no significant impact on project economics when analysed. Many cases revealed that 10 kW turbines are not feasible projects under the Feed-in Tariff program and that turbines begin to become economical around 35 kW. / University of Guelph, Natural Sciences and Engineering Research Council of Canada (NSERC), the Poultry Industry Council (PIC), Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), and Egg Farmers of Ontario

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.

This thesis examines the design of supervisory controllers for windfarms of pitch-controlled wind turbines. The control objectives are the maximisation of the financial income from the generated electricity and the minimisation of the turbines' fatigue damage. The design exploits the wide variations in the ratio of financial income to fatigue damage which are found both spatially across windfarms and as a function of time. The supervisory control strategy makes use of the ability of pitch-controlled turbines to operate with variable power set points; a capability which is rarely exploited in practice. A windfarm simulation which has been developed for the purposes of testing supervisory controllers is described. It is shown that the simulation is a suitable test-bed for this application. Results are presented which demonstrate how the fatigue damage of a turbine's gearbox and structural components vary as functions of the mean wind-speed, turbulence intensity and power set point, both for isolated turbines and for turbines experiencing wake effects. A lifetime performance function is proposed and 'ideal' power set point curves are evaluated using a genetic search algorithm. It is shown that significant improvements in performance can be achieved if the operation of the turbines is altered to take account of variable electricity tariffs. A windfarm control strategy that splits the turbines into interacting and non-interacting categories is found to give good results. Using data generated by the simulation, it is shown that simple cost functions can be developed for non-interacting turbines which, when used in a controller, give performance that is close to the 'ideal'. A similar cost function is applied to a group of three interacting turbines, and it is found that substantial reductions in all measures of total annual fatigue damage are achieved for a small reduction in total annual financial income. The on-line implementation of windfarm supervisory controllers is discussed and the behaviour of a simple hill-climbing algorithm is examined using a simulated group of three interacting turbines.

Wind is a fast growing energy resource and the demand for clean energy is increasing with growing interests from media, governmental institutions and the public (EWEA, 2004). The increased interest towards the wind energy market has led to a more competitive environment where it is crucial for a project developer to select projects most likely to succeed, in terms of profitability, among alternatives on the market. To enable such selection, an evaluation process is often applied. Furthermore, traditional evaluation processes are often performed at completion of a project where an early indication of a project’s potential profitability is often missing (Samset &amp; Christensen, 2015). At the early phase of a wind energy project the multiple factors influencing the project’s outcome are often conflicting and contain high level of uncertainty and the evaluation process becomes complex (Kumar et al., 2017). In addition, these factors are difficult to quantify and to determine their relative weight of importance (Çolak &amp; Kaya, 2017). This thesis aims to problematise the early project phase by contributing with a practical tool for evaluating wind energy projects at this phase. In addition, the thesis aims to contribute with an identification and monetarily quantification of the important factors to assess when doing so. The thesis is conducted as a case study at a company developing wind energy projects in Sweden. Due to the multiple factors that influencing a project’s outcome, MCDM (multi-criteria decisionmaking) analysis is used as the research process to create the tool. Findings from this study show that key factors that are possible to quantify at an early phase are conditions for civil works, grid conditions, wind resource and electricity price area. In general, their relative importance, measured in relative increase of IRR, is wind resource, electricity price area, grid conditions and civil works in the descending order. This study has four contributions, three theoretical and one practical. Firstly, the study confirms MCDM as a suitable analysis to use, when creating an evaluation model for wind energy projects. Secondly, the study confirms most of the important factors mentioned in the literature to assess when evaluating a wind energy project. However, this study contributes with insights that only conditions for civil works, grid conditions, wind resource and electricity price area can be quantified for the purpose of creating an evaluation tool at an early phase. Thirdly, previous studies have focused less on determining the relative weight of importance of the relevant key factors and this study contributes by quantifying and determining which of these key factors that are of relevance in an evaluation. Lastly, this study contributes practically by creating an evaluation tool suggested to be used by the case company to compare different projects on the market and form investment decisions based on financial data. Furthermore, the tool facilitates an equal evaluation process for all projects, thus leading to a more standardised decision-making process where the case company can focus their resources on the projects most likely to succeed. / Vind är en snabbväxande energiresurs där efterfrågan efter grön energi ökar från media, statliga myndigheter och allmänheten. Det ständigt ökande intresset av vindenergi har lett till en allt mer konkurrenskraftig marknad där det är viktigt för en projektutvecklare att välja de projekt som är mest troliga att bli lönsamma bland de tillgängliga projekten på marknaden. Dessa urval sker oftast genom en projektutvärderingsprocess. Dock sker merparten av de traditionella projektutvärderingarna i slutet av ett projekt där en tidig indikation rörande ett projektet lönsamhet oftast saknas (Samset &amp; Christensen, 2015). Anledningen till detta är att vindkraftsprojekt består av flera motsägande faktorer med en hög osäkerhet som påverkar ett projekts resultat, vilket leder till en komplex utvärderingsprocess i ett tidigt skede (Kumar et al., 2017). Dessutom är dessa faktorer svåra att kvantifiera vilket gör det svårt att vidare bestämma deras relation i förhållande till varandra (Çolak &amp; Kaya, 2017). Detta examensarbete ämnar därför till att problematisera den komplexa utvärderingsprocessen i ett tidigt skedde genom att skapa ett praktiskt verktyg för en simplifierad utvärderingsprocess av vindkraftsprojekt. Detta examensarbete är utformat som en fallstudie på ett företag i Sverige som utvecklar vindkraftsprojekt. På grund av antalet faktorer som påverkar projektens lönsamhet används MCDM-analys som forskningsprocess för att skapa verktyget. Resultat från denna studie visar att de nyckelfaktorer som är möjliga att kvantifiera i det tidiga skede är: infrastruktur, nätanslutning, vindresurs och elprisområde. Resultaten visar även att faktorernas påverkan, mätt i relativ ökning av IRR, är i fallande ordning: vindresurs, elprisområde, nätanslutning och infrastruktur och att dessa, i fallande ordning, är relevanta att utvärdera. Denna studie har totalt fyra bidrag, varav tre teoretiska och ett praktiskt bidrag. Det första bidraget är en konfirmation av att MCDM är en lämplig analysmetod vid skapandet av utvärderingsverktyget. Det andra bidraget är en konfirmation av de faktorer som nämns i litteraturen som viktiga vid en utvärderingsprocess i ett tidigt skede. Dock är endast faktorerna infrastruktur, nätanslutning, vindresurs och elprisområde möjliga att kvantifiera i detta skede. Det tredje bidraget är kunskap gällande faktorernas förhållande till varandra och vilka som är relevanta att utvärdera. Det praktiska bidraget är utvärderingsverktyget där företaget rekommenderas att använda det för att jämföra olika projekt på marknaden och fatta välinformerade beslut baserat på finansiell data. Dessutom bidrar verktyget med en likvärdig utvärderingsprocess för alla projekt vilket leder till en mer standardiserad beslutsprocess där företaget kan fokusera sina resurser på de projekt som är mest troliga att bli lönsamma.

The Thesis shows the perspectives of involving renewable energy resources into the energy balance of Russia, namely the use of wind energy for the purpose of energy supply for the objects of the Russian Gas transportation system. The methodology of the wind energy technical potential calculation is designed and the wind energy technical potential assessment for onshore and offshore zones of Russia is presented. The analysis of Russian Gas transportation system in terms of energy consumption is carried out when comparing the map of wind resources in Russia with the map of Russian Gas transportation system and the perspective of wind turbines installation is shown in order to offset energy consumption of the selected object of the Gas transportation system. The decision-making algorithm for wind turbines selection is developed for installation on the wind farm. Also indicators of investment attractiveness of the project of using wind turbines for compression stations energy supply were calculated.

Sweden has a great potential for offshore wind energy production. As technology develops and policies change, construction of offshore wind farms in the country is likely to increase. The presented methodology is to apply MCDM and AHP methods in a GIS to produce an evaluation map of potential sites for offshore wind energy production.  The aim of this thesis was to determine what data is relevant and needed to translate Swedish and international standards and regulations regarding offshore wind farm siting into one or more layers of GIS data within the exclusive economic zone of Sweden. Furthermore the locations of the existing Areas of National Interests for offshore wind energy production have been evaluated using the evaluation map. The evaluation map has been obtained using several exclusionary criteria and buffer distances as well as four evaluation criteria. In addition, the results of this study have been used to calculate a potential net annual energy production for offshore wind energy in Sweden. The analysis considers some of the social, technical and environmental constraints present in offshore wind farm siting. The exclusion, buffer and evaluation criteria were determined in the initial literature review of previous studies on the topic. Datasets were collected from several different open online resources and Swedish government agencies, the analysis was performed using the QGIS software. To assess the results, the resulting evaluation map has been classified into four different categories: poor, average, good and excellent. The analysis shows that it is possible to translate Swedish and international standards into one layer of GIS data. Furthermore the results of this study show that 52% of the defined Areas of National Interest for offshore wind energy production should not be considered for wind farm siting according to the exclusion constraints, additionally only 19% of the Areas of National Interest for offshore wind energy production are classified as good or excellent. In contrast, 20.3% of the entire study area is deemed to be suitable for offshore wind farm siting, out of which 62.7% is classified as good or excellent. The potential net annual energy production has been estimated to be 56.1 TWh annually within the Areas of National Interest for offshore wind energy production and 915.3 TWh annually within the entire study area. / Sverige har en stor potential för produktion av havsbaserad vindkraft. När teknologin utvecklas och de politiska förutsättningar förändras, kommer konstruktionen av havsbaserad vindkraft i landet troligtvis öka. Den presenterade metodologin går ut på att använda MCDM och AHP metoder i ett GIS för att producera en utvärderingskarta för potentiella platser att producera havsbaserad vindenergi.  Målet med den här studien har varit att ta reda på vilken data som krävs och är relevant för att överföra svensk samt internationell standard och regler kring placeringen av havsbaserad vindkraft till ett eller flera lager av GIS data inom Sveriges exklusiva ekonomiska zon. Vidare har de existerande riksintressena för havsbaserad vindkraft utvärderats med hjälp av utvärderingskartan. Denna karta har blivit framtagen med hjälp av flertalet buffertzoner samt exkluderings- och fyra stycken utvärderingskriterier. Slutligen har studiens resultat används för att beräkna en potentiell årlig energiproduktion för offshore vindkraft i Sverige. Studien beaktar några av de sociala, tekniska och miljömässiga begränsningar som finns för havsbaserad vindenergi. Buffertzonerna samt exkluderings- och utvärderingskriterierna har bestämts med hjälp av en inledande litteraturstudie av tidigare forskning på ämnet. Den datan som använts i analysen har inhämtats från flera olika öppna onlineresurser samt från svenska myndigheter. Den efterföljande analysen har genomförts med hjälp av programmet QGIS. För att möjliggöra en kvantifiering av resultaten har utvärderings kartan omklassificerats till fyra olika kategorier: “poor”, “average”, “good” samt “excellent”. Studien visar att det är möjligt att överföra svensk samt internationell standard och regler till ett lager av GIS data. Resultatet visar att att enbart 48% av arean inom de definierade riksintressena för havsbaserad vindkraft bör beaktas vid allokering av havsbaserad vindenergi, enligt de begränsningar som definierats i denna studie. Vidare påvisar resultatet att enbart 19% av arean inom de utpekade riksintressena för vindkraft kan klassificeras som “good” eller “excellent”. Samtidigt påvisar studien att 20.3% av studieområdet bedöms som lämpligt för allokering av havsbaserad vindkraft, av dessa lämpliga områden klassificeras 62.7% som “good” och “excellent”. Den potentiella årliga energiproduktionen uppskattas till 56.1 TWh inom riksintressena för havsbaserad vindkraft samt till 915.3 TWh inom hela studieområdet.

<p>In this research, a Split-Shaft Wind Energy Conversion System (SS-WECS) is investigated</p> <p>to improve the performance and cost of the system and reduce the wind power</p> <p>uncertainty influences on the power grid. This system utilizes a lightweight Hydraulic Transmission</p> <p>System (HTS) instead of the traditional gearbox and uses a Doubly-Fed Induction</p> <p>Generator (DFIG) instead of a synchronous generator. This type of wind turbine provides</p> <p>several benefits, including decoupling the shaft speed controls at the turbine and the generator.</p> <p>Hence, maintaining the generator’s frequency and seeking maximum power point</p> <p>can be accomplished independently. The frequency control relies on the mechanical torque</p> <p>adjustment on the hydraulic motor that is coupled with the generator. This research provides</p> <p>modeling of an SS-WECS to show its dependence on mechanical torque and a control</p> <p>technique to realize the mechanical torque adjustments utilizing a Doubly-Fed Induction</p> <p>Generator (DFIG). To this end, a vector control technique is employed, and the generator</p> <p>electrical torque is controlled to adjust the frequency while the wind turbine dynamics</p> <p>influence the system operation. The results demonstrate that the generator’s frequency is</p> <p>maintained under any wind speed experienced at the turbine.</p> <p>Next, to reduce the size of power converters required for controlling DFIG, this research</p> <p>introduces a control technique that allows achieving MPPT in a narrow window of generator</p> <p>speed in an SS-WECS. Consequently, the size of the power converters is reduced</p> <p>significantly. The proposed configuration is investigated by analytical calculations and simulations</p> <p>to demonstrate the reduced size of the converter and dynamic performance of the</p> <p>power generation. Furthermore, a new configuration is proposed to eliminate the Grid-</p> <p>Side Converter (GSC). This configuration employs only a reduced-size Rotor-Side Converter</p> <p>(RSC) in tandem with a supercapacitor. This is accomplished by employing the hydraulic</p> <p>transmission system (HTS) as a continuously variable and shaft decoupling transmission</p> <p>unit. In this configuration, the speed of the DFIG is controlled by the RSC to regulate the</p> <p>supercapacitor voltage without GSC. The proposed system is investigated and simulated in</p> <p>MATLAB Simulink at various wind speeds to validate the results.</p> <p>Next, to reduce the wind power uncertainty, this research introduces an SS-WECS where the system’s inertia is adjusted to store the energy. Accordingly, a flywheel is mechanically</p> <p>coupled with the rotor of the DFIG. Employing the HTS in such a configuration allows the</p> <p>turbine controller to track the point of maximum power (MPPT) while the generator controller</p> <p>can adjust the generator speed. As a result, the flywheel, which is directly connected</p> <p>to the shaft of the generator, can be charged and discharged by controlling the generator</p> <p>speed. In this process, the flywheel energy can be used to modify the electric power generation</p> <p>of the generator on-demand. This improves the quality of injected power to the</p> <p>grid. Furthermore, the structure of the flywheel energy storage is simplified by removing</p> <p>its dedicated motor/generator and the power electronics driver. Two separate supervisory</p> <p>controllers are developed using fuzzy logic regulators to generate a real-time output power</p> <p>reference. Furthermore, small-signal models are developed to analyze and improve the MPPT</p> <p>controller. Extensive simulation results demonstrate the feasibility of such a system and its</p> <p>improved quality of power generation.</p> <p>Next, an integrated Hybrid Energy Storage System (HESS) is developed to support the</p> <p>new DFIG excitation system in the SS-WECS. The goal is to improve the power quality</p> <p>while significantly reducing the generator excitation power rating and component counts.</p> <p>Therefore, the rotor excitation circuit is modified to add the storage to its DC link directly.</p> <p>In this configuration, the output power fluctuation is attenuated solely by utilizing the RSC,</p> <p>making it self-sufficient from the grid connection. The storage characteristics are identified</p> <p>based on several system design parameters, including the system inertia, inverter capacity,</p> <p>and energy storage capacity. The obtained power generation characteristics suggest an energy</p> <p>storage system as a mix of fast-acting types and a high energy capacity with moderate</p> <p>acting time. Then, a feedback controller is designed to maintain the charge in the storage</p> <p>within the required limits. Additionally, an adaptive model-predictive controller is developed</p> <p>to reduce power generation fluctuations. The proposed system is investigated and simulated</p> <p>in MATLAB Simulink at various wind speeds to validate the results and demonstrate the</p> <p>system’s dynamic performance. It is shown that the system’s inertia is critical to damping</p> <p>the high-frequency oscillations of the wind power fluctuations. Then, an optimization approach</p> <p>using the Response Surface Method (RSM) is conducted to minimize the annualized</p> <p>cost of the Hybrid Energy Storage System (HESS); consisting of a flywheel, supercapacitor, and battery. The goal is to smooth out the output power fluctuations by the optimal</p> <p>size of the HESS. Thus, a 1.5 MW hydraulic wind turbine is simulated, and the HESS is</p> <p>configured and optimized. The direct connection of the flywheel allows reaching a suitable</p> <p>level of smoothness at a reasonable cost. The proposed configuration is compared with the</p> <p>conventional storage, and the results demonstrate that the proposed integrated HESS can</p> <p>decrease the annualized storage cost by 71 %.</p> <p>Finally, this research investigates the effects of the reduced-size RSC on the Low Voltage</p> <p>Ride Through (LVRT) capabilities required from all wind turbines. One of the significant</p> <p>achievements of an SS-WECS is the reduced size excitation circuit. The grid side converter is</p> <p>eliminated, and the size of the rotor side converter (RSC) can be safely reduced to a fraction</p> <p>of a full-size excitation. Therefore, this low-power-rated converter operates at low voltage</p> <p>and handles the regular operation well. However, the fault conditions may expose conditions</p> <p>on the converter and push it to its limits. Therefore, four different protection circuits are</p> <p>employed, and their effects are investigated and compared to evaluate their performance.</p> <p>These four protection circuits include the active crowbar, active crowbar along a resistorinductor</p> <p>circuit (C-RL), series dynamic resistor (SDR), and new-bridge fault current limiter</p> <p>(NBFCL). The wind turbine controllers are also adapted to reduce the impact of the fault</p> <p>on the power electronic converters. One of the effective methods is to store the excess energy</p> <p>in the generator’s rotor. Finally, the proposed LVRT strategies are simulated in MATLAB</p> <p>Simulink to validate the results and demonstrate their effectiveness and functionality.</p>

Thesis (M.Tech.: Civil Engineering)-Dept. of of Civil Engineering and Surveying, Durban Institute of Technology, 2005 xii, 89 leaves : ill. ; 30 cm / The Reconstruction and Development Programme adopted by the Government of National Unity is more than a list of the services required to improve the quality of life of the majority of South Africans. It is not just a call for South Africans to unite to build a country free of poverty and misery; it is a programme designed to achieve this objective in an integrated and principled manner. Based on the strategic objectives, as highlighted in the White Paper on Water Supply and Sanitation Policy, with regard to alleviating the chronic potable water shortages in South Africa, this thesis investigates a design methodology to supply potable water through the use of wind energy. The design focuses on small rural off-grid developments where grid electricity either has not or will not reach, and where renewable energy is the only viable option. This thesis provides an overview of wind energy and presents the fundamentals of wind power calculations. It also formulates an overview of the historic and present situation with regards to potable water supply, and reflects on the need for urgent intervention. The feasibility of using wind energy to supply potable water to rural communities in South Africa is explored in a case study. The various problem areas are identified and examined and a wide range of possible solutions are recommended. A final flow chart for the system design is proposed, thus ensuring comprehensive design methodology from which future design of similar systems can be based.