Submerged arc welding (SAW) is commonly used for fabricating large diameter linepipes, pressure vessels and wind turbine towers due to its high deposition rate, high quality welds, ease of automation and low operator skill requirement. In order to achieve high melting efficiency required for high productivity, best weld quality and good mechanical properties in manufacturing industries, the welding process parameters need to be optimized. In this study, the effect of SAW current and speed on the physical and mechanical properties of ASME SA516 Gr. 70 (pressure vessel steel) and ASTM A709 Gr. 50 (wind turbine tower steel) were investigated. Three welding currents (700 A, 800 A and 850 A) and four travel speeds (5.9, 9.3, 12.3 and 15.3 mm/s) were used to weld sample plates measuring 915 mm x 122 mm x 17 mm. The weld quality and properties were evaluated using weld geometry measurements, visual inspection, ultrasonic inspection, hardness measurements, optical microscopy, tensile testing, Charpy impact testing and scanning electron microscopy. It was found that the physical and mechanical properties of the weldments were affected by SAW parameters. Severe undercuts were found at high travel speed and welding current. Low heat input caused lack of penetration defects to form in the weldments. The welding process melting efficiency (WPME) achieved was up to 80%. The hardness of the coarse grain heat affected zone (CGHAZ) and the weld metal increased with travel speed. The toughness of both materials increased with increasing travel speed and welding current. The yield and tensile strengths of the weldments of SA516 Gr.70 and A709 Gr.50 steels were within the same range as those of their respective parent metals because all test specimens broke in the parent metals. Also, the parent metals of both steels had the highest fracture strain and percent elongation. The percentage elongation increased with travel speed but decreased with welding current.

In this thesis, a grid-connected wind-energy converter system including a matrix converter is proposed. The matrix converter, as a power electronic converter, is used to interface the induction generator with the grid and control the wind turbine shaft speed. At a given wind velocity, the mechanical power available from a wind turbine is a function of its shaft speed. Through the matrix converter, the terminal voltage and frequency of the induction generator is controlled, based on a constant V/f strategy, to adjust the turbine shaft speed and accordingly, control the active power injected into the grid to track maximum power for all wind velocities. The power factor at the interface with the grid is also controlled by the matrix converter to either ensure purely active power injection into the grid for optimal utilization of the installed wind turbine capacity or assist in regulation of voltage at the point of connection. Furthermore, the reactive power requirements of the induction generator are satisfied by the matrix converter to avoid use of self-excitation capacitors. The thesis addresses two dynamic models: a comprehensive dynamic model for a matrix converter and an overall dynamical model for the proposed wind turbine system. The developed matrix converter dynamic model is valid for both steady-state and transient analyses, and includes all required functions, i.e., control of the output voltage, output frequency, and input displacement power factor. The model is in the qdo reference frame for the matrix converter input and output voltage and current fundamental components. The validity of this model is confirmed by comparing the results obtained from the developed model and a simplified fundamental-frequency equivalent circuit-based model. In developing the overall dynamic model of the proposed wind turbine system, individual models of the mechanical aerodynamic conversion, drive train, matrix converter, and squirrel-cage induction generator are developed and combined to enable steady-state and transient simulations of the overall system. In addition, the constraint constant V/f strategy is included in the final dynamic model. The model is intended to be useful for controller design purposes. The dynamic behavior of the model is investigated by simulating the response of the overall model to step changes in selected input variables. Moreover, a linearized model of the system is developed at a typical operating point, and stability, controllability, and observability of the system are investigated. Two control design methods are adopted for the design of the closed-loop controller: a state-feedback controller and an output feedback controller. The state-feedback controller is designed based on the Linear Quadratic method. An observer block is used to estimate the states in the state-feedback controller. Two other controllers based on transfer-function techniques and output feedback are developed for the wind turbine system. Finally, a maximum power point tracking method, referred to as mechanical speed-sensorless power signal feedback, is developed for the wind turbine system under study to control the matrix converter control variables in order to capture the maximum wind energy without measuring the wind velocity or the turbine shaft speed.

The environmental and monetary cost of energy has renewed interest in horizontal-axis wind turbines (HAWT). One problem with HAWT design is turbulent winds, which cause cyclic loading and reduced life. Controlling short-term aerodynamic fluctuations with blade pitching or mechanical flaps is limited by the speed of actuation. The objective was to investigate using jet-flap-like fluidic actuators on the 'suction surface' of an aerofoil for rapid aerodynamic control. A NACA 0025 aerofoil was constructed for wind-tunnel experiments. The low Reynolds number (Re) flow was measured non-intrusively with particle image velocimetry (PIV). The jet showed limited effect compared to published work. The sharp trailing edge and distance to the jet were determined to be critical factors. At Re≈100000 the 'suction surface' jet sheet is less useful for control than the conventional 'pressure surface' sheet. The experiment suggests usage near the blade root on truncated aerofoils.

Wind turbines operating in cold climate are exposed to periods of icing which lowers the plantprofitability by affecting the annual production. The loss of production has two components:The first (and most important) component is reduced power during operation due to disturbedaerodynamic properties of the blades. The second component is increased standstill. During this thesis project, methods to estimate production losses of a wind farm due to icinghave been developed, as well as a software tool to facilitate the use of these methods and thepresentation of the results. A method based on common metrological data and availableproduction data was desired, as modelling ice-related losses is expensive and may be inaccurate. The methods developed are based on using measured data for each turbine, such as activepower, temperature, wind direction and wind speed, and through this data describe theindividual turbine’s performance during different conditions. Production losses were thenestimated by comparing actual and expected power output (for the given wind speed). Thethesis then expanded on this basic concept by using reanalysis and mesoscale modelled data,which offers greater variety in the way estimating the losses may be performed, as well as theoption to derive losses for periods not covered by the production data. It was also important to develop a flexible and portable method that could incorporate newseasons of data or estimate losses for different wind farms with a completely differentconfiguration of turbines. The methods are developed using data from a wind farm in northern Sweden, consisting of 40Vestas V90 turbines and constructed a few years ago. It was found that eastern position in the wind farm and turbine altitude correlates with higherice-related losses, and that easterly winds relate to higher such losses than westerly winds. Thelosses during operation were estimated to 6.4 % of annual possible production and stops due toicing to 2.1 % of the total time. The losses figures are comparable to an earlier study performedin 2011 based on the same wind farm. The possibility of anti- or deicing systems for the wind farm and the profitability of such aninvestment should be further investigated as the wind farm is expected to continue operation fortwenty years or more.

No description available.

Management system for enhancing transfer of knowledge in wind power industry has not received sufficient research attention in recent times. In some cases, the wind power plant owner does not control the management system for operation and maintenance activities. Most of these wind power plants are under contract and rely upon the turbine vendor to perform most of the maintenance works and subsequently share their experience at the initial stage of operation. This research investigates the management system for the operations and maintenance activities of the offshore wind plant in Lillgrund. The research also explores the type of learning method that was adopted by the wind turbine vendor (Siemens) to transfer the operation and maintenance knowledge to the operator and owner (Vattenfall) within the speculated period. It was realized that in the next one year, the Vattenfall would be in full control of the operations and maintenance activities of the offshore wind power plant in Lillgrund. The co-management arrangement will give Siemens a good reputation and gainful experience in the wind power industry. The arrangement is achievable due to Siemens strategy to strive for constructive and long-standing relationships with their customer, based on trust, respect, and honesty. Vattenfall on the other hand, is aiming to be the partner of choice for their suppliers at the same time as best serving their internal customers. The provision for the training during the co-management period enables Siemens to strengthen their relationship with Vattenfall in this industry. In addition, Siemens also maintain close relationship with their customers and develop a large part of their portfolio, frequently on site. Vattenfall improves profitability and value creation, as a fundamental prerequisite for continued growth. The management systems of Vattenfall can be related to professional bureaucracy, this is due to the fact that it was organized to accommodate Siemens experts. Vattenfall benefits from the co-management activities of the operation and maintenance of the Lillgrund wind power plant for a specific period of time. The outcome of the research work has proven that there is an effective time-dependent proportionality for a gradual transfer of the technical knowledge of operation and maintenance from Siemens Wind AB to the Vattenfall personnel. The research started from the perspective of the maintenance method by Swedish standard for wind power, and the way things are being carried out in a more practical way in Lillgrund plant.

In several countries that have been early in the development of wind farms, there is today a second hand market for the used wind turbines. The European Union (EU) has established a waste hierarchy in order to minimize throwaway mentality. The second hand market is a part of this as the steps are to minimize, reuse, recycle, extract energy and landfill. In order to promote the development of renewable energy, there are energy certificates for the producers that provide it, wind power being one type of renewable energy. After 15 years the energy certificates for a specific wind turbine are no longer paid, and after that there are several different scenarios for the wind turbine. The scenarios investigated in this bachelor’s thesis are export of the wind turbine to countries that are not as far along as Sweden in their development towards renewable energy, selling in Sweden to individuals, and recycling of the wind turbine, as it mostly consists of metals and therefore is recyclable. In these three scenarios it is assumed that the sites for wind turbines are being reused for new larger wind turbines that produce more energy. Two additional scenarios are to reduce the number of wind turbines in a wind farm by half, in this way gaining access to free spare parts for the remaining wind turbines and continued operation, i.e. operate them for as long time as possible. To assure the decommissioning of the wind turbines and restoration of the site, there are several economical choices for the operator of the wind turbine. No matter what choice is made, the total amount should be 500 000 SEK according to the permission for the wind turbine. A Swedish authority, Miljöprövningsdelegationen, decides whether the operators choice in reassuring and make a decision based on that. To see which scenario is most profitable the economical part is crucial in this bachelor’s thesis. As a wind turbine is a large investment, the investment calculation is sensitive even to small changes. Inflation, interest rate, electricity price and energy certificate price can all vary a good deal but as it is almost impossible to predict the development of these factors, the inflation, interest rate and energy certificate price are all on a fixed level in this report. The electricity price is assumed to be dependent of the inflation solely. By using these assumptions and Microsoft Excel it has been clear that selling the wind turbine and reuse the site for a new larger wind turbine is the most profitable. Sweden has the goal to have 30 TWh, equivalent to 20 %, electricity from wind until year 2020. Today the part is 6.5 TWh, equivalent to 4 %. To make this goal reality it is necessary to make the permitting process easier and faster than the case is today. If Sweden compares to Denmark they already have 28 % electricity from wind and they aim for 50 %. / I flera länder som har legat i framkant med att uppföra vindkraftsparker finns idag en andrahandsmarknad för verken. Inom Europeiska Unionen (EU) har en avfallshierarki upprättats för att minska slit- och slängmentaliteten. Andrahandsmarknaden är en del i detta då stegen är minimera, återanvända, återvinna, energiutvinna och deponera. För att främja utvecklingen av förnyelsebar el finns elcertifikat till de producenter som tillhandahåller detta, däribland vindkraft. Efter 15 år slutar elcertifikatet att utbetalas för ett specifikt vindkraftverk, och då finns olika scenarier för vindkraftverket. De scenarier som undersöks i detta examensarbete är export av verket till länder som inte kommit lika långt som Sverige med förnyelsebar energi, försäljning inom Sverige till privatpersoner och återvinning av verket, som främst består av metaller och därmed är återvinningsbart. I dessa tre scenarier avses det att samma plats återanvänds för nya större verk som producerar mer. Ytterligare två scenarier är att halvera antalet verk i en park och på så vis få tillgång till gratis reservdelar till de återstående verken samt fortsatt drift av verket, det vill säga köra dem så länge det går. För att säkerställa nedmontering av vindkraftverk och återställning av platsen finns olika ekonomiska alternativ för verksamhetsutövaren. Oavsett vilket alternativ som väljs ska summan resultera i 500 000 kronor per vindkraftverk enligt tillståndet till verket. Miljöprövningsdelegationen (MPD) avgör om verksamhetsutövarens valda alternativ är betryggande och beslutar utifrån det. För att se vad som är det mest lönsamma scenariot spelar den ekonomiska delen en stor roll för arbetet. Eftersom vindkraft är en stor investering blir investeringskalkylen känslig även för små förändringar. Inflationen, räntan, elpriset och elcertifikatpriset är poster som kan variera mycket men eftersom det är i princip omöjligt att förutspå hur utvecklingen kommer se ut är inflationen, räntan och elcertifikatpriset satt på en fast nivå. Elpriset är sedan beroende av inflationen. Med hjälp av dessa antaganden och Microsoft Excel har det mest lönsamma scenariot tagits fram vilket är att sälja verket och sätta upp ett nytt större på platsen. Sverige har som mål att fram till år 2020 ha 30 TWh, motsvarande 20 %, el från vindkraft i elnätet. Idag är andelen 6,5 TWh, motsvarande 4 %. För att detta ska bli verklighet måste tillståndsprocessen förenklas och gå snabbare än vad fallet är idag. Jämförs Sverige med Danmark har de redan 28 % vindkraftsel och siktar på 50 %.

In this thesis, a grid-connected wind-energy converter system including a matrix converter is proposed. The matrix converter, as a power electronic converter, is used to interface the induction generator with the grid and control the wind turbine shaft speed. At a given wind velocity, the mechanical power available from a wind turbine is a function of its shaft speed. Through the matrix converter, the terminal voltage and frequency of the induction generator is controlled, based on a constant V/f strategy, to adjust the turbine shaft speed and accordingly, control the active power injected into the grid to track maximum power for all wind velocities. The power factor at the interface with the grid is also controlled by the matrix converter to either ensure purely active power injection into the grid for optimal utilization of the installed wind turbine capacity or assist in regulation of voltage at the point of connection. Furthermore, the reactive power requirements of the induction generator are satisfied by the matrix converter to avoid use of self-excitation capacitors. The thesis addresses two dynamic models: a comprehensive dynamic model for a matrix converter and an overall dynamical model for the proposed wind turbine system. The developed matrix converter dynamic model is valid for both steady-state and transient analyses, and includes all required functions, i.e., control of the output voltage, output frequency, and input displacement power factor. The model is in the qdo reference frame for the matrix converter input and output voltage and current fundamental components. The validity of this model is confirmed by comparing the results obtained from the developed model and a simplified fundamental-frequency equivalent circuit-based model. In developing the overall dynamic model of the proposed wind turbine system, individual models of the mechanical aerodynamic conversion, drive train, matrix converter, and squirrel-cage induction generator are developed and combined to enable steady-state and transient simulations of the overall system. In addition, the constraint constant V/f strategy is included in the final dynamic model. The model is intended to be useful for controller design purposes. The dynamic behavior of the model is investigated by simulating the response of the overall model to step changes in selected input variables. Moreover, a linearized model of the system is developed at a typical operating point, and stability, controllability, and observability of the system are investigated. Two control design methods are adopted for the design of the closed-loop controller: a state-feedback controller and an output feedback controller. The state-feedback controller is designed based on the Linear Quadratic method. An observer block is used to estimate the states in the state-feedback controller. Two other controllers based on transfer-function techniques and output feedback are developed for the wind turbine system. Finally, a maximum power point tracking method, referred to as mechanical speed-sensorless power signal feedback, is developed for the wind turbine system under study to control the matrix converter control variables in order to capture the maximum wind energy without measuring the wind velocity or the turbine shaft speed.

The environmental and monetary cost of energy has renewed interest in horizontal-axis wind turbines (HAWT). One problem with HAWT design is turbulent winds, which cause cyclic loading and reduced life. Controlling short-term aerodynamic fluctuations with blade pitching or mechanical flaps is limited by the speed of actuation. The objective was to investigate using jet-flap-like fluidic actuators on the 'suction surface' of an aerofoil for rapid aerodynamic control. A NACA 0025 aerofoil was constructed for wind-tunnel experiments. The low Reynolds number (Re) flow was measured non-intrusively with particle image velocimetry (PIV). The jet showed limited effect compared to published work. The sharp trailing edge and distance to the jet were determined to be critical factors. At Re≈100000 the 'suction surface' jet sheet is less useful for control than the conventional 'pressure surface' sheet. The experiment suggests usage near the blade root on truncated aerofoils.

Experimental aeroacoustic research was conducted on a wind turbine specific airfoil at low Reynolds numbers. The goal of this thesis was to study trailing edge noise generation from the airfoil and investigate correlations between the noise and the flow field. Before experiments were performed the current wind tunnel had to be modified in order to make it more suitable for aeroacoustic tests. Sound absorbing foam was added to the inside of the tunnel to lower the background noise levels and turbulence reduction screens were added which lowered the turbulence. An S822 airfoil was chosen because it is designed for low Reynolds flows attainable in the wind tunnel which are on the order of 104. Smoke wire flow visualization was used to gain insight into the airfoil wake development and oil film flow visualization was used to qualitatively assess the boundary layer development. Laser Doppler anemometry (LDA) was used to measure two components of velocity at high data rates in the airfoil wake. Wake profiles were measured in addition to single point measurements to determine the velocity spectrum. A microphone was mounted inside the test section in order to measure the trailing edge noise. Initial plans included measuring the trailing edge noise with a microphone array capable of quantifying and locating noise sources. Although an array was built and beamforming code was written it was only used in preliminary monopole source tests. Oil film results showed the behaviour of the boundary layer to be consistent with previous low Reynolds number experiments. LDA results revealed sharp peaks in the velocity spectra at 1100 Hz from U0 = 15–24 m/s, and 3100 and 3800 Hz, from U0 = 25–35 m/s, which were inconsistent with vortex shedding results of previous researchers. Also present were a series of broad peaks in the spectra that increase from 1200–1700 Hz in the U0 = 25–35 m/s range. The shedding frequency from the smoke wire flow visualization was calculated to be 1250 Hz at U0 = 26 m/s. These sharp peaks were also present in the acoustic spectrum. It was reasoned that these peaks are due to wind tunnel resonance which is a common occurrence in hard wall wind tunnels. In particular the tone at 1100 Hz is due to a standing wave with a wavelength equal to half the tunnel width. The shedding frequency from the smoke wire flow visualization was calculated to be 1100 Hz at U0 = 20 m/s. These tones exhibited a “ladder-like” relationship with freestream velocity, another aspect indicative of wind tunnel resonance. It was reasoned that the wind tunnel resonance was forcing the shedding frequency of the airfoil in the U0 = 15–24 m/s range, and in the U0 = 25–35 m/s range, the shedding frequency corresponded to the broad peaks in the LDA spectra.