M.Ing. / The synchronous reluctance machine is a reasonably unknown type of machine. Recent developments have made it possible to deliver more power than an induction machine of similar size. It must, however, be noted that to accomplish this, the rotor profile design becomes complex and also expensive to manufacture. The aim of this project is to explore the possibility of controlling a synchronous reluctance machine `sensorlessly' (with no speed or position feedback sensors). The specific synchronous reluctance machine was made from an induction machine by machining a profile into the rotor cage of the induction machine. The required profile was designed using finite element analysis of the magnetic structure of the machine. A model of the machine was developed through using the direct and quadrature axis approach. With a model of the machine an estimator could be designed. This estimator was used to calculate the load angle of the machine by measuring the phase voltages and line currents and then estimating from these measurements the actual load angle. The estimator was designed for steady state conditions and gave sufficiently accurate values for the load angle under these conditions. The estimator was used as feedback in the torque control of the machine and it was shown that better results could be achieved with a better rotor profile. The partial cage of the induction machine present in the rotor made the machine more robust to changes in load. More research can be done on the modelling of the partial cage as well as the influence it has on the synchronous reluctance machine. Torque control and speed control were achieved with step changes in load of up to eighty percent of rated value. The performance of the machine was poor compared to an induction machine, but should improve with improvement in rotor profile design.

The use of communication strategies (CSs) has been of interest on research into second language acquisition (SLA) since it can help learners to attain mutual comprehension effectively and develops understanding of interaction in SLA research. This study investigates and clarifies a wide range of CSs that learners of English and learners of Chinese use to solve language problems as well as to facilitate problem-free discourse in both text-based and video-based SCMC environments. Seven Chinese-speaking learners of English and seven English-speaking learners of Chinese were paired up as tandem (reciprocal) learning dyads in this study. Each dyad participated in four interactions, namely, text-based SCMC in English, text-based SCMC in Chinese, video-based SCMC in English and video-based SCMC in Chinese. The interaction data were analysed along with an after-task questionnaire and stimulated reflection to explore systematically and comprehensively the differences between text-based and video-based SCMC and differences between learners of English and learners of Chinese. The results showed that learners used CSs differently in text-based and video-based SCMC compared with their own performance and indicated different learning opportunities provided by these two modes of SCMC. Although the difference in language was less salient than the medium effect, learners of English and learners of Chinese tended to have their own preferences for particular CSs. When these preferences appear to reflect an appropriate communicative style in one particular culture, learners might need to raise their awareness of some strategies during intercultural communication to avoid possible misunderstanding or offence. Some possible advantages of tandem learning interaction were also identified in this study, such as the potential to develop sociocultural and intercultural competence due to the opportunity to practice culturally appropriate language use with native speakers in a social context.

Ultra high frequency (UHF) radio frequency identification (RFID) systems suffer from issues that limit their widespread deployment and limit the number of applications where they can be used. These limitations are: lack of a well defined read zone, interference, and environment sensitivity. To overcome these limitations a novel receiver device is introduced into the system. The use of such device or devices mitigates the issues by enabling more "anchor points" in the system. Two such devices exist in industry and academia: the Astraion Sensatag and the Gen2 Listener. The drawbacks of the Sensatag is that it offers poor performance in capturing tag signals. The Gen2 Listener is based on the expensive software defined radio hardware. The purpose of the thesis was to develop a receiver that will enable several new RFID applications that are not available with current RFID systems. The receiver, named ARR (Augmented RFID Receiver), receives tag and reader signals, which are decoded by an FPGA and the results are reported through Ethernet. This device is central to the augmented RFID system. To show the suitability of such an approach, the performance of the implementation was compared to the other two outlined solutions. A comparison of the read rate and range of the implementations were the defining factors. The analysis showed that the ARR is capable of receiving tag signals with a read rate of 50% for passive and 66% for semi-passive tags at a one meter distance and is capable of receiving tag signals at a maximum of 3.25 meters for passive and 5.5 meters for semi- passive tags, with the reader being within 8 meters of the ARR. Two applications were implemented to showcase the ARR: an RFID portal and protocol analyzer.

Wind power generation has gained a large share in the renewable energy market over the past few years. This study investigates the impact of large scale penetration of permanent magnet synchronous generator (PMSG) based wind turbines on power quality of the grid. PMSGs are attractive due to the absence of a gearbox in the drive-train, which results in lower maintenance costs and higher reliability. Moreover, the advancements in power electronics have facilitated PMSGs to generate optimal power at varying wind speed conditions. This is achieved through the use of maximum power point tracking algorithms. The drawbacks of PMSG-based wind energy systems are that they inject harmonics into the network and cause flicker as well as other power quality issues. Despite these disadvantages, the grid code requires that PMSGs stay connected to the grid even under grid disturbances. This is because the reactive power control capability of PMSG-based wind energy systems can actually assist with voltage support. It will be shown in this study that disconnecting large scale PMSGs based wind turbines during grid disturbances has a detrimental effect on transient stability of the grid. This study will show that PMSG-based wind energy systems improve transient stability and assist in voltage support through reactive power control. Moreover, the impacts of large scale PMSG based wind turbines on power quality of the grid can be reduced by various means, which are also addressed in the study.

Syftet med föreliggande studie är att bidra med ökad kunskap om e-lärande i arbetslivet. E-lärande har i föreliggande studie definierats i enlighet med Clark och Mayers (2016) som; ”instruktion levererad på en digital enhet och som är menad att främja lärandet [egen översättning]” (2016, s. 38). Emellertid har studien valt att begränsa sig till endast dator som digital enhet. Föreliggande studie belyser även multimedia inom e-lärande som relevant då multimedia utgör en vital del av e-lärande. För att besvara studiens syfte användes två frågeställningar för att undersöka; (1) medarbetares upplevelse av e-lärande och (2) medarbetares upplevelse av multimedia inom e-lärande. Båda inom kontexten för arbetsplatslärande. Baserat på studiens syfte valdes en kvalitativ ansats där studiens material har bestått av semistrukturerade intervjuer med medarbetare inom den offentliga sektorn. Materialet har utifrån teoretiska begrepp och utgångspunkter bearbetats och analyserats genom en tematisk analys. Resultatet påvisade att vilka delar och hur delarna var utformade påverkar medarbetares upplevelse av e-lärande på arbetsplatsen. Resultatet tydde på att syftet med e-lärandet, tidsuppfattningen av e-lärande och vilken typ av kommunikation som inkluderades hade påverkan på medarbetares upplevelse av e-lärande på arbetsplatsen. Vidare visar resultatet att ett inkluderande av multimedia är en främjande faktor för lärandet vilket påvisar dess påverkan på medarbetares upplevelse av multimedia inom e-lärande. Emellertid tyder resultatet på att för mycket information som presenteras genom multimedia är hämmande för lärandet och således påverkar även det medarbetares upplevelse av multimedia inom e-lärande. / The purpose of this study has been to contribute with increased knowledge about e-learning in workplaces. E-learning have in this study been defined as “instruction delivered on a digital device (such as a desktop computer, laptop computer, tablet, or smartphone) that is intended to support learning” (Clark & Mayer, 2016, s. 38) which is in accordance with the definition by Clark and Mayers (2016). However, this study chosen to limit the definition too only include computer as the digital device. Multimedia can be seen as an important part of e-learning and therefore multimedia has been included in this study. In order for the study to serve its purpose two separate research question has been defined to examine; (1) employee’s experience of e-learning and (2) employee’s experience of multimedia in e-learning. Both in the context of workplace learning. Based on the purpose of the study a qualitative method has been chosen and the research materials have consisted of semi-structured interviews with employees in the public sector. Based on the study’s theoretical framework, the research materials have been analyzed through a thematic analysis. The presented result shows that employee’s experience of e-learning is affected by which component of e-learning and the content of the components of e-learning is used. It’s shown that the purpose of e-learning, time and the ability to collaborate with others are key components of e-learning. Furthermore, including multimedia is enhancing for learning which indicates its effect on the employee’s experience of multimedia in e-learning. However, the results indicate that too much information presented through multimedia can impede the learning and therefore the employee’s experience of multimedia in e-learning is affected by the amount of information presented.

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Low Earth orbit represents a valuable limited natural resource. Of particular interest are sun-synchronous orbits; it is estimated that approximately 44% of low Earth satellites are sun-synchronous. A previously developed sun-synchronous orbit slot architecture is considered. An in-depth analysis of the relative motion between satellites and their corresponding slots is performed. The long-term evolution of Earth's orbital environment is modeled by a set of coupled ordinary differential equations. A metric for quantifying the benefit, if any, of implementing a sun-synchronous architecture is developed. The results indicate that the proposed slot architecture would reduce the frequency of collisions between satellites in sun-synchronous orbits.

In this Master´s thesis will be performed an analysis of thermal properties of synchronous machines in the program Ansys Workbench on a simplified model of synchronous traction motor. In the first section will be performed thermal analysis without cooling followed by analysis of air flow and finally thermal analysis with cooling for fan speed 1500 min-1 and 3000 min-1. The second section will describe the principle, construction and losses on the synchronous machine. The third chapter will describe concepts such as heat, temperature, heat transfer, types of the heat transfer, specific heat capacity, emisivity and thermal conductivity. The fourth chapter will introduce the program Ansys Workbench, finite element method and Ansys CFX. In the fifth chapter will be described how to perform thermal analysis on the created model of motor. The sixth chapter will describe how to analyze the air flow of the created model of motor. The flow analysis will be performed for fan speed 1500 min-1 and 3000 min-1. In the seventh chapter will be compared the results of the air flow and pressure field in the motor model. In the eighth chapter will be performed a thermal analyzis on the created motor model with cooling for fan speed 1500 min-1 and 3000 min-1. The nineth chapter will compare the results of temperatures and heat fluxes obtained from the thermal analysis witnout cooling, with cooling for fan speed 1500 min-1 and 3000 min-1 for full losses, half losses of continous running, and full losses of interrupt running for 9000 seconds (2 hours 30 minutes).

This master’s thesis is focused on the analysis of the excitation current in synchronnous machines. Contains a description of excitation systems for synchronous machines, meaning and design of the sliding contact ant its representation in electrical machines. The main part of the work is focused on the evaluation of the field current of the three plants. The work includes graphic record of the excitation current of the hydroelectric power station Slapy, provided record from the power plant Opatovice was for evaluating load of turbo-generators. Provided record from the nuclear power plant Temelín was for evaluating.current division into individual brushes. The conclusion is a summary of the achieved knowledge.

My work will not inform you only with the issue of magnetic field, but also with design complications such as: proposal winding, analysis cogging, the machine connection to infinite bus and independent network and their solutions in the design of electrical machine. In the introductory chapter, we tried to offer the most accurate theory of magnetic fields because it is hard to understand that episodes of physical design of the machine is our alpha and omega. Shows the results of the program RMxprt and Maxwell, where we simulate the synchronous machine with the connection nominal load. The results of the program are verified and compared with calculations.