1,721,021 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Converter Design for Nuna Maximum Power Point Tracker
No full textThe world is rapidly moving towards a greener future, a mainstay of which is solar energy. Hence, maximum power point trackers, or MPPTs for short, are an indispensable component, since these devices provide one with the capability to fully maximize the achievable power from solar cells in a system. A symbol of the greener world that is evolving around us is the biannual World Solar Challenge, where state-of-the-art solar powered cars race against one another through the deserts of Australia. This thesis forms the link between these two elements: to design an MPPT optimally suited towards the requirements of the Nuna Solar Car. Commercially available MPPTs are not particularly well suited for the specific demands of such a bleeding edge race. They are mostly designed for high power or low voltage systems. The MPPT designed during this thesis is optimized for high efficiency and other requests stated by the Nuon Solar Team members. The design of the MPPT has been split into several parts. This thesis is focused on the converter within the MPPT. It presents the result of research, design exploration, simulation and testing. The results obtained with the prototype that has been built show the designs correctness and conformance to the requirements, with an efficiency of up to 98,5%.Bachelor EEElectrical Power EngineeringElectrical Engineering, Mathematics and Computer Scienc
Maximum Power Point Tracking Topology, sensor and switch design
No full textThe Nuna 6 is a solar racing vehicle that solely relies on solar energy from the sun. Every year, the team seeks ways to improve the performance of their car. One way to improve the performance is to maximize the power output of the solar panels on top of the car. Maximizing the power output can be done with a 'Maximum Power Point Tracker'. The aim of this thesis was to develop an improved, distributed 'Maximum Power Point Tracking'-system which optimizes the power efficiency of the solar panel array of the Nuna 6 solar racing vehicle. To prove that the proposed distributed topology is more power effificient when compared to a central tracking topology, simulations of the total Nuna 6 electrical system were performed. Based on the simulation results, together with Nuna 6 specifications, a DC-DC boost converter was designed. Validation of the design was done by simulation with the Nuna 6 model. After validation, a breadboard proof-of-concept was built. The proof-of-concept was successfully tested and compared with earlier simulations. The system design process was evaluated and recommendations for further study and future real-life implementations were formulated. The simulation results prove that the proposed distributed tracking system is as much as 40% more efficient in large insolation differences and 10% in small insolation differences. The system excels when insolation differs, however it is slightly less efficient when used with equal insolation on every panel. The developed proof of concept demonstrates a functioning maximum power point tracker and DC-DC boost converter. The power efficiency of the boost converter was found to be between 95:8% and 98:5%, with an efficiency of 97:1% for the rated input power of 200W.Electrical EngineeringElectrical Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Maximum power point tracking: Algorithm and software development
No full textCurrently, the Nuon Solar Team is building their new solar car, which makes use of solar panels. Solar panels have a Maximum Power Point (MPP), which, when operated at that point, ensures the maximum available power is obtained from them. In this thesis, different options were explored to solve the problem of tracking the MPP of a solar panel. The focus of this thesis was the software part of tracking the MPP and the goal of this thesis was to implement the most efficient algorithm that works in fast changing levels of irradiance and when thesolar panels are partially shaded. In order to realize this goal, we first did a literature survey to learn about the available algorithms and their respective advantages and disadvantages. Subsequently, we chose the algorithms which had potential and we could realistically implement. Those algorithms were P&O, In ond and their adaptive variants. We simulated those algorithms for their efficiencies in Simulink and implemented them onto a microcontroller. Lastly, we made an experimental setup and measured the algorithms for their efficiencies. The results showed that based on the simulations, the adaptive InCond algorithm is the most efficient algorithm, also in fast changing levels of irradiance. As the simulation did not simulate partially shaded solar panels, we can not make any conclusions about the performance of the different algorithms in that case. In the experimental setup, we verified that the controller and all implemented algorithms worked correctly. However, we were not able to verify all the simulation results, as we could only only test the sudden shading condition. The MPPT was able to reliably track the MPP of a solar panel, depending on what algorithm was used. Some algorithms were more susceptible to noise than others, and eventually we concluded that the adaptive P&O algorithm performed best in the experimental setup, because it is least susceptible to noise and has the advantages of an adaptive algorithm. We did not measure the efficiency of the MPPT. However, based on the simulations and the measured efficiencies of the other subsystems of the MPPT, we are confident that we succeeded in designing and implementing an MPPT algorithm with an efficiency of at least 95%.Electrical EngineeringElectrical Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Weight and Volume Optimization of a Three-phase Inverter
No full textThree-phase inverters are widely used in industries. Due to the advancements in semiconductor technologies, researchers have witnessed a continuous increase in the power density of inverters over the decades. Meanwhile, on the basis of such advancement, designers are also pushing the power density to its limit by minimizing the weight and volume of every sub-system in the inverter such as EMI filter, cooling system, DC-link, etc. More often than not, these studies only look into one individual sub-system and do not consider the correlation between different sub-systems. This study explores the optimization of the weight and volume of a three-phase inverter system with a different approach. In this thesis, essential designing variables and sub-systems are considered simultaneously. To accomplish this goal, a thorough investigation of the case study inverter system is introduced; crucial sub-systems and designing variable will be picked out. Then an effective and efficient system model is constructed to evaluate different system designs. In the final step, NSGA-II optimization algorithm is applied to obtain Pareto optimal inverter designs. The optimization results are presented and analyzed to shed light upon guidance which designers could follow. It is believed that the proposed optimization procedure could effectively assist designers in the early stage of the designing task.Electrical EngineeringESEElectrical Engineering, Mathematics and Computer Scienc
GaN enabled OLED Driver for Automotive Lighting Application
No full textThe impressive features, both in a design and technical aspect, of the Organic LED (OLED) lighting technology have attracted the interest of the research and commercial world and have recently be in the spotlight of the automotive industries, like the Lighting Department of Audi. Some of the most exciting features of these lights are the exibility, transparency and the very small thickness. It is reasonable, therefore, that in order to take full advantage of this new technology the electronics that drive these lights, that is the dc/dc converter, should also be characterised of low prole, exibility and small size. A boost towards the direction of the converter minimization and high power density operation could be the recently commercialised power switching technology of Gallium Nitride (GaN) devices. This technology, which exploits the advantages of the wide band gap semiconductors, offers high frequency, high power density, low switching losses operation and low profle design, as well. As every newly commercialised technology, the areas of application that at most exploit the advantages of these switches are still to be found, but it is expected that applications that require high power density or low profle features, like the OLED applications, could benefit the most from the GaN technology. This area is the exact topic of the current master thesis. At this project a dc/dc converter based on GaN switching devices is designed and built. The converter is purposed for the driving of Organic LED lights that belong to the tail light system of a vehicle. As such, the electrical, mechanical and thermal specifications of the converter are based on the guidelines of the Lighting Department of the Audi automotive industry and the nature of the Organic LED lighting. At this thesis, the required dc/dc converter is designed, built, measured and assessed for its adequacy to the defined requirements. During the design part of this project the necessary simulations are conducted. For the purpose of estimating the losses of the GaN device a detailed analytical model for the switching transients is used. Also, both the possibilities of using a planar and a discrete coil are investigated during the simulations and the two components, which were built in the lab, are compared experimentally. A final prototype of the converter is also built in the lab and the experimental and simulated results are then compared and assessed. The assessment of the results showed that the features of the GaN device can be fully exploited at this application and can offer the low profile and high power density requirements. In order, however, to achieve the minimization of the magnetic component more advanced and wider range of core materials are required, especially if a planar coil is desired. Finally, full exploitation of the detailed analytical GaN loss model requires specialised software tools or accurate analytical models in order to determine the values of the various parasitics and the thermal resistance of the component, both strongly related to the PCB layout. This, also, means that during the design procedure in order to achieve better accuracy -which is required at applications which push the frequency to the limits - the PCB design layout parameters should be included in the iterative process of the parameter specificationElectrical Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc
A modular DC/DC converter using SiC switches for railway applications
No full textElectrical trains are fed with a high voltage to reduce transmission losses. In the train, these voltages have to be stepped down to a voltage that could be fed into the traction motors. This is done with IGBT based power converters. The use of IGBTs in power converters has some disadvantages: they generate a lot of heat and are therefore not suitable for high-frequency operation. Developing power modules for electrical traction also has an other disadvantage: there is no standard electrification voltage. So for every customer a new converter has to be developed. These problems could be solved by using silicon carbide (SiC) based high voltage switches in a modular converter. The SiC switches enable high-frequency operation at high voltages and thus the reduction of the converter size. In a modular converter, multiple modules could be connected in series and/or parallel in such a way that the input voltage and output current is divided equally among the modules. During this thesis project, a SiC based modular converter was designed, build and evaluated.Electrical Engineering, Mathematics and Computer ScienceElectrical Sustainable EnergyMSc Electrical Engineering - Electrical Sustainable Energy trac
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