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OFFSHORE wind farms need to develop technologies that fulfill three main objectives:Efficiency, power density and reliability. The purpose of this thesisis to study an HVDC transmission system based on series connection of the turbineswhich theoretically meet these three objectives. A new topology of matrixconverter operated at high frequency is proposed. This converter is studied usingdifferent modulation algorithms. Simulation and experimental results demonstratedthat the converter can be operated as a current source converter with highefficiency. An optimal control based on a linear quadratic regulator is proposedto control the matrix converter as well as the converter placed on shore. Resultsdemonstrated the high performance of this type of control and its simplicity forimplementation. An stationary state study based on non-linear programming andMontecarlo simulation was carried out to determine the performance of the conceptfor long-term operation. Series connection is an efficient technology if and only ifthe differences in the effective wind velocity are small. This aspect limits the numberof wind turbines that can be connected in series, since a numerous number ofturbines will lead to high covariances in the distribution of the wind. A complementarystudy about active filter and reactive power compensation was carried outusing an optimization-based algorithm.

Vindkraft är ett miljövänligt energislag med stor utvecklingspotential, både i Sverige ochutomlands. I det här examensarbetet sammanfattas de viktigaste bitarna av kunskapen sombehövs för att förstå sig på vindkraft, med fokus på meteorologi och kommunikation medkonsultföretag i branschen. På grundval av litteratur i ämnet, konsultrapporter beställda av ettsvenskt företag i branschen och diskussion med experter ges här en grundläggande översikt imeteorologi för vindkraft, vilken innefattar kunskaper om klimatet i allmänhet ochvindklimatet i synnerhet, förståelse för luftens flöde, den geostrofiska vinden och hurtopografi och dylikt påverkar luftens strömning i gränsskiktet. Vidare diskuteras hur energin ivinden tas till vara, med en sammanfattning av viktiga tekniska detaljer; vindkraftsspecifikastorheter och uttryck, energiförluster och effekterna av att placera många vindkraftverk i engrupp; vakeffekten. En av de dominerande delarna av alla konsultrapporter som studerats ärhur man analyserar och behandlar vinddata för maximering av tillförlitlighet och relevans. Föratt en mätserie ska kunna användas för att förutsäga framtida vindar måste dennormalårskorrigeras, antingen med hjälp av andra mätserier, avancerade fysikaliska modellerav strömningen, eller både och. Osäkerheter uppkommer alltid, och en diskussion kring hur deolika konsultbolagen behandlar dem görs. Slutligen diskuteras olika sätt att förbättrakvaliteten på både beställning av rapport och slutprodukten från konsulten, utifrån ett antalfrågor ställda av ovan nämnda företag och författaren själv. Resultatet sammanfattas nedan.En mycket viktig del av utvecklingen står vindkraftprojekteringsföretag för. Företagen ibranschen behöver ha goda kunskaper i meteorologi för att bli framgångsrika. De måste ocksåkunna kommunicera sina kunskaper på ett klart och precist sätt. Företagen måste också kunnalära av andra i samma bransch och av andra med specialistkunskaper. För företag utan egnameteorologer anställda är det viktigt att kommunikationen och det ömsesidiga lärandet mellankonsult- och beställarbolag sker på ett professionellt, men samtidigt stöttande och lärande, sätt.Beställaren måste lära sig vad man ska beställa och vara tydlig med vad man kräver avkonsulten. Konsulten måste i sin tur vara tydlig med val av metod, tillvägagångssätt ochbegärande av rätt material som underlag för sina studier. En ny infallsvinkel som intediskuteras i rapporterna fast den kanske borde det är klimatförändringarnas påverkan på detlångsiktiga klimatet. Faktum är att trenden under 1900-talet inte visar någon större långsiktigförändring av medelvinden, men de årliga variationerna kan vara stora och tenderar att varierai cykler som skulle kunna utnyttjas för att maximera framgången för vindkraften. / Wind power is an environmentally friendly energy source with a considerable growthpotential, in Sweden as well as abroad. In this Bachelor’s thesis work, the most importantparts of the knowledge needed to understand wind power, is summarized. The focus is onmeteorology and communication with wind power consultants by a Swedish wind powercompany. With the basis of relevant literature, consultancy reports and discussion withsubject experts, is here provided a basic synopsis of wind power meteorology, which includesknowledge of the climate in general, and the wind climate specifically, understanding of thegeneral flow of the wind, the geostrophic wind in particular, and how topography and similarground features affect the boundary layer flow. Furthermore it is discussed how the windenergy content is harnessed, briefly going over some technical details, wind power specificquantities and expressions, energy losses and the effects of bundling wind power plants closetogether: wake effects. One of the dominant parts of all wind consultancy reports studied hereis how to analyze wind data series to maximize accuracy and relevance. A trustworthymeasuring series good enough to predict future wind energy content needs to be long termcorrected using other, longer measuring series as reference, or checked against an advancedphysically accurate mesoscale flow model, or both. Uncertainties are always a part of theequation, and a discussion over how the different wind power consultants treat theseuncertainties is made. Finally there is a discussion about different measures that can be madeto improve quality on both detailing orders for wind power consultancy reports and the finalproduct delivered to the client. The results are summarized in the next paragraph.Wind power developers are a major influence on how wind power research is shaped. A goodknowledge of meteorology is a key to success for wind power industry businesses.Communication with industry expert companies is also paramount. Clearly and precisely,companies need to learn from, and communicate with, other wind power enterprises, scientificexperts and researchers. Wind power companies without their own meteorologists have aneven bigger need of this professional contact with other businesses providing themeteorological expertise they need. Contacts need to be supportive and teaching. The clientneeds to learn what to order in detail and what they expect from the report. The providercompany needs to be detailed about their selection of methods and procedure. Consultantsshould be equally detailed in requisition of base data from the client. A point of view notpresent in the studied consult reports is climate change and how it affects the long term windclimate. As a matter of fact the Scandinavian 20th century average wind trend is neutral, butyear-to-year variations can be quite significant and tend to vary in cycles possible to exploitfor wind power success.

The value of an easy to install, accurate, far-reaching measurement instrument is easily understood when dealing with setting up and monitoring wind power parks. However the use of remote sensing equipment when doing this is a subject of much discussion amongst professional experts and scholars. This is especially the case when the environmental conditions are difficult, such as areas with complex terrain or cold climate (or both), for example forested, hilly or mountainous regions in north Europe and North America. The remote sensing technology SODAR provides for detailed 3-dimensional datasets, but need a skilled analyst to make sure the measurements are realistic. This thesis is aimed at verifying the accuracy of the SODAR wind measuring equipment at two potential wind power parks in Sweden. It has been done by comparing the wind speed, wind direction and turbulence measured by an AQ Systems AQ500 Wind Finder SODAR to the wind speed, wind direction and turbulence measured by in situ anemometers mounted in nearby meteorological masts. The comparison was made by calculation of statistical parameters such as correlation and root mean square error. The results of this investigation shows that the differences in the measured quantities are site specific and that i t‟s very difficult to distinguish between differences arising from ambient conditions, the measurement method and the method of calculating comparable values. It is clear, however, that conditions such as temperature, inhomogeneous fetch and wind speed are contributors to the observed discrepancies. When compensating for these various sources of error; such as eliminating data from malfunctioning equipment, icing conditions, mast wake and forest flow disturbance, the SODAR wind speed data shows a very high correlation with the mast anemometer data, giving a correlation coefficient of around 0.90 – 0.95. / Värdet av ett mätinstrument som är lätt att installera, noggrant och som kan mäta högt upp i troposfären är lätt att inse när man har att göra med att installera och övervaka vindkraftparker. Det har dock funnits en debatt om huruvida fjärranalytiska mätningar är tillräckliga för sådana ändamål i expert- och akademikerkretsar. Debatten spetsas ytterligare till då omgivningarna är svåra, exempelvis i områden med komplex terräng eller kallt klimat (eller både och), till exempel skogbeklädda, kulliga eller bergiga områden i norra Europa och Nordamerika som är aktuella för exploatering av vindkraft. Det fjärranalytiska redskapet SODAR förser exploatören med detaljerade tredimensionella datasamlingar, men kräver en erfaren och skicklig analytiker för att verkligen verifiera att mätresultaten är realistiska och tillförlitliga. Detta examensarbete har som mål att verifiera noggrannheten hos SODAR-utrustning vid två potentiella vindkraftparker i Sverige. Det har gjorts genom att jämföra vindhastighet, vindriktning och turbulens mätt med en AQ Systems AQ500 Wind Finder SODAR med vindhastighet, vindriktning och turbulens mätt med anemometrar i närbelägna meteorologiska mätmaster. Jämförelsen gjordes genom att beräkna statistiska parametrar som korrelation och standardavvikelse. Resultatet av undersökningen visar att skillnaderna i de uppmätta storheterna är specifika för varje mätplats och att det är mycket svårt att särskilja bidragen till skillnaderna mellan omgivande förhållanden, mätmetoder och beräkningsmetoder. Det står dock klart att förhållanden så som temperatur, inhomogen omgivande skrovlighet på anloppssträckan och vindhastigheten i sig själv bidrar till de observerade skillnaderna i mätresultat. Kompenseras felaktig och störd data bort så visar vindhastigheten mätt med SODAR en mycket god korrelation med mastanemometerdata, med en korrelationskoefficient omkring 0,90 – 0,95.

Long time average wind conditions at potential wind turbine sites are of great importance when deciding if an investment will be economically safe. Wind climate estimates such as these are traditionally done with in situ measurements for a number of months. During recent years, a wind climate database has been developed at the Department of Earth Sciences, Meteorology at Uppsala University. The database is based on model runs with the higher order closure mesoscale MIUU-model in combination with long term statistics of the geostrophic wind, and is now used as a complement to in situ measurements, hence speeding up the process of turbine siting. With this background, a study has been made investigating how well actual power productions during the years 2004-2006 from 21 Swedish wind turbines correlate with theoretically derived power productions for the corresponding sites. When comparing theoretically derived power productions based on long term statistics with measurements from a shorter time period, correction is necessary to be able to make relevant comparisons. This normal year correction is a main focus, and a number of different wind energy indices which are used for this purpose are evaluated. Two publicly available (Swedish and Danish Wind Index) and one derived theoretically from physical relationships and NCEP/NCAR reanalysis data (Geostrophic Wind Index). Initial testing suggests in some cases very different results when correcting with the three indices and further investigation is necessary. An evaluation of the Geostrophic Wind Index is made with the use of in situ measurements. When correcting measurement periods limited in time to a long term average, a larger statistical dispersion is expected with shorter measurement periods, decreasing with longer periods. In order to investigate this assumption, a wind speed measurement dataset of 7 years were corrected with the Geostrophic Wind Index, simulating a number of hypothetical measurement periods of various lengths. When normal year correcting a measurement period of specific length, the statistical dispersion decreases significantly during the first 10 months. A reduction to about half the initial statistical dispersion can be seen after just 5 months of measurements. Results show that the theoretical normal year corrected power productions in general are around 15-20% lower than expected. A probable explanation for the larger part of this bias is serious problems with the reported time-not-in-operation for wind turbines in official power production statistics. This makes it impossible to compare actual power production with theoretically derived without more detailed information. The theoretically derived Geostrophic Wind Index correlates well to measurements, however a theoretically expected cubed relationship of wind speed seem to account for the total energy of the wind. Such an amount of energy can not be absorbed by the wind turbines when wind speed conditions are a lot higher than normal. / Vindklimatet vid tänkbara platser för uppförande av vindkraftverk är avgörande när det beslutas huruvida det är en lämplig placering eller ej. Bedömning av vindklimatet görs vanligtvis genom vindmätningar på plats under ett antal månader. Under de senaste åren har en vindkarteringsdatabas utvecklats vid Institutionen för Geovetenskaper, Meteorologi vid Uppsala universitet. Databasen baseras på modellkörningar av en högre ordningens mesoskale-modell, MIUU-modellen, i kombination med klimatologisk statistik för den geostrofiska vinden. Denna används numera som komplement till vindmätningar på plats, vilket snabbar upp bedömningen av lämpliga platser. Mot denna bakgrund har en studie genomförts som undersöker hur bra faktisk energiproduktion under åren 2004-2006 från 21 vindkraftverk stämmer överens med teoretiskt härledd förväntad energiproduktion för motsvarande platser. Om teoretiskt härledd energiproduktion baserad på långtidsstatistik ska jämföras med mätningar från en kortare tidsperiod måste korrektion ske för att kunna göra relevanta jämförelser. Denna normalårskorrektion genomförs med hjälp av olika vindenergiindex. En utvärdering av de som finns allmänt tillgängliga (Svenskt vindindex och Danskt vindindex) och ett som härletts teoretiskt från fysikaliska samband och NCEP/NCAR återanalysdata (Geostrofiskt vindindex) görs. Inledande tester antyder att man får varierande resultat med de tre indexen och en djupare utvärdering genomförs, framförallt av det Geostrofiska vindindexet där vindmätningar används för att söka verifiera dess giltighet. När kortare tidsbegränsade mätperioder korrigeras till ett långtidsmedelvärde förväntas en större statistisk spridning vid kortare mätperioder, minskande med ökande mätlängd. För att undersöka detta antagande används 7 års vindmätningar som korrigeras med det Geostrofiska vindindexet. I detta simuleras ett antal hypotetiskt tänkta mätperioder av olika längd. När en mätperiod av specifik längd normalårskorrigeras minskar den statistiska spridningen kraftigt under de första 10 månaderna. En halvering av den inledande statistiska spridningen kan ses efter endast 5 månaders mätningar. Resultaten visar att teoretiskt härledd normalårskorrigerad energiproduktion generellt är ungefär 15-20% lägre än väntat. En trolig förklaring till merparten av denna skillnad är allvarliga problem med rapporterad hindertid för vindkraftverk i den officiella statistiken. Något som gör det omöjligt att jämföra faktisk energiproduktion med teoretiskt härledd utan mer detaljerad information. Det teoretiskt härledda Geostrofiska vindindexet stämmer väl överens med vindmätningar. Ett teoretiskt förväntat förhållande där energi är proportionellt mot kuben av vindhastigheten visar sig rimligen ta hänsyn till den totala energin i vinden. En sådan energimängd kan inte tas till vara av vindkraftverk när vindhastighetsförhållandena är avsevärt högre än de normala.

Wind tunnel studies of the wake behind model wind turbines with one, two and three blades have been made in order to get a better understanding of wake development as well as the possibility to predict the power output from downstream turbines working in the wake of an upstream one. Both two-component hot-wire anemometry and particle image velocimetry (PIV) have been used to map the flow field downstream as well as upstream the turbine. All three velocity components were measured both for the turbine rotor normal to the oncoming flow as well as with the turbine inclined to the free stream direction (the yaw angle was varied from 0 to 30 degrees). The measurements showed, as expected, a wake rotation in the opposite direction to that of the turbine. A yawed turbine is found to clearly deflect the wake flow to the side showing the potential of controlling the wake position by yawing the turbine. The power output of a yawed turbine was found to depend strongly on the rotor. The possibility to use active wake control by yawing an upstream turbine was evaluated and was shown to have a potential to increase the power output significantly for certain configurations. An unexpected feature of the flow was that spectra from the time signals showed the appearance of a low frequency fluctuation both in the wake and in the flow outside. This fluctuation was found both with and without free stream turbulence and also with a yawed turbine. The non-dimensional frequency (Strouhal number) was independent of the freestream velocity and turbulence level but increases with the yaw angle. However the low frequency fluctuations were only observed when the tip speed ratio was high. Porous discs have been used to compare the meandering frequencies and the cause in wind turbines seems to be related to the blade rotational frequency. It is hypothesized that the observed meandering of wakes in field measurements is due to this shedding. / QC 20101018

AIM: As global warming is a fact and the consumption of energy is continuously increasing, alternative sourcing of energy is a must. The use of oil and coal for heating is limited due to it is nature resource which is also limited. Everyone will be forced to evaluate their own usage of energy and look into the alternatives of how to be a part of solving this global issue. For many, alternatives such as sun panels and wind power stations could be an alternative power source.   Today, there is only a limited availability in Sweden of small sized wind power stations and only small local producers or importers that sell the equipment – mostly through internet based market communications.   Method: The theoretical approach to this thesis is based on the MIO model in combination with several other models and tools such as, PESTEL, Marketing Mix, SWOT, Porter’s five forces, EVC and STP.   Result & Conclusions: There is a market for small wind power stations between 5 – 50 kW in Sweden. The biggest reason why the market segment exist and will increase is due to continuously increasing energy prices and that wind power stations of this size are permitted to be connected directly to household consumption.   Suggestions for future research: How are other energy complements like solar panels influenced? What governmental decisions affect the business of small wind power stations?   Contributions to the thesis: Success in this segment requires a different approach to product offering than what the current competition is doing.

This thesis presents the concept of a "distributed HVDC converter" for offshore wind farms. The proposed converter topology allows series interconnection of wind turbines obviating the necessity of transformers and an offshore platform. Each wind turbine is equipped with a 5MW permanent-magnet synchronous generator and an ac-dc-dc converter. The converter topology is a diode rectifier (ac-dc) cascaded with a single-switch step-down converter (dc-dc). The dc-dc stage allows the current to flow at all times in the dc link while regulating generator torque. The receiving end is equipped with a conventional thyristor-based HVDC converter. The inverter station is located onshore and it regulates the dc link current to be constant. Stability of the configuration and independent operation of the wind turbines are validated through simulations using the PSCAD/EMTDC software package. Protection for some key dc fault scenarios are discussed and a possible protection strategy is proposed.

This dissertation presents dynamic reactive power control of isolated power systems. Isolated systems include MicroGrids in islanded mode, shipboard power systems operating offshore, or any other power system operating in islanded mode intentionally or due to a fault. Isolated power systems experience fast transients due to lack of an infinite bus capable of dictating the voltage and frequency reference. This dissertation only focuses on reactive control of islanded MicroGrids and AC/DC shipboard power systems. The problem is tackled using a Model Predictive Control (MPC) method, which uses a simplified model of the system to predict the voltage behavior of the system in future. The MPC method minimizes the voltage deviation of the predicted bus voltage; therefore, it is inherently robust and stable. In other words, this method can easily predict the behavior of the system and take necessary control actions to avoid instability. Further, this method is capable of reaching a smooth voltage profile and rejecting possible disturbances in the system. The studied MicroGrids in this dissertation integrate intermittent distributed energy resources such as wind and solar generators. These non-dispatchable sources add to the uncertainty of the system and make voltage and reactive control more challenging. The model predictive controller uses the capability of these sources and coordinates them dynamically to achieve the voltage goals of the controller. The MPC controller is implemented online in a closed control loop, which means it is self-correcting with the feedback it receives from the system.

This thesis presents the concept of a "distributed HVDC converter" for offshore wind farms. The proposed converter topology allows series interconnection of wind turbines obviating the necessity of transformers and an offshore platform. Each wind turbine is equipped with a 5MW permanent-magnet synchronous generator and an ac-dc-dc converter. The converter topology is a diode rectifier (ac-dc) cascaded with a single-switch step-down converter (dc-dc). The dc-dc stage allows the current to flow at all times in the dc link while regulating generator torque. The receiving end is equipped with a conventional thyristor-based HVDC converter. The inverter station is located onshore and it regulates the dc link current to be constant. Stability of the configuration and independent operation of the wind turbines are validated through simulations using the PSCAD/EMTDC software package. Protection for some key dc fault scenarios are discussed and a possible protection strategy is proposed.