1,720,953 research outputs found
Design of high temperature, 800V, 40kW, Silicon Carbide based, full scale inverter demonstrator for aerospace applications
No full textThis thesis focusses on the design of a loss optimized, Silicon Carbide (SiC) based, 800V, multi kilowatt three phase inverter prototype for aerospace application, targeted for high temperature ambient conditions. Given the multiple design constraints such as spatial envelope, mass and efficiency optimization, this research addresses multiple topics that influence the objective. It begins with the overall loss modelling of the inverter, analysis of 2 – level inverter architecture (implementing multiple devices in parallel) to optimize efficiency at high temperatures, impact of paralleling multiple SiC MOSFETs on efficiency, etc.
It then proceeds with analytical modelling of SiC MOSFET switching characteristics with the aim to improve the accuracy of estimation as compared to the existing models. Specifically, the impact of drain to source voltage, junction temperature and load parasitic elements on the switching dynamics is modelled to enhance the accuracy. It is ensured that this modelling methodology relies only on the information provided in the datasheet of the device, which eliminates the need for additional tests to improve the accuracy of loss estimation and thereby saves time and cost. The proposed modelling strategy is verified experimentally by building a suitable double pulse test bench setup.
Further, the key aspects of suitable component selection and placement, PCB layout strategies that suits the temperature requirement, total mass and efficiency targets are delved into. The commutation loop parasitic inductance that impacts the turn off voltage overshoot and thereby the choice of gate resistance that directly impacts the overall efficiency of the inverter is optimized. Suitable placement of multilayer copper planes under the DC link capacitors, in the PCB is analyzed using ANSYS Q3D tool to address the same. Also, the choice of placement of paralleled SiC MOSFETs that gives a tradeoff between either minimizing the commutation loop inductance or minimizing the asymmetry in current sharing between paralleled devices is analyzed. Critical elements of high voltage, high power rated PCB design, such as switching node copper placement, isolation of high voltage and low voltage copper areas and the components that form the boundary between them are discussed. Since SiC MOSFET have lower junction capacitances, they can be switched at high speeds to optimize efficiency. This results in high rate of change in voltages, more so when the design is rated for 800V. The design of gate driver circuitry that can carry out the same, while ensuring minimal cross coupling between power and signal areas of the layout is presented. The full scale prototype is validated extensively at multiple DC link voltages from 400V to 800V and at across a wide range of load upto 30 kW. The impact of load and DC link on efficiency is experimentally recorded. Furthermore, the impact of paralleling of SiC MOSFETs on overall converter efficiency and junction temperature are experimentally observed through temperature logging and power analyzer measurements. To further analyze the variation of the inverter’s efficiency with load and DC link, a MATLAB – Simulink based simulation, that takes into account the device’s switching and conduction losses, based on manufacturer datasheet information, is built. The simulation result exhibited a decent match with the experimental results and also helped deep dive into the distribution of semiconductor losses and their variation with operating conditions. Simulation study is further used to compare the SiC MOSFETs with similar figure of merits but with different chip areas. This helped bring out the load ranges where each device choice would result in maximum efficiency. To improve the accuracy of
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the Simulink based model that estimates the inverter’s efficiency, the switching loss look up tables are replaced with the switching loss estimated using the accurate analytical models developed and discussed in the previous chapters of this thesis. This resulted in improved accuracy of efficiency estimates.
The experimental device current waveforms captured during the exhaustive validation of the full scale prototype, revealed the asymmetric sharing of currents between paralleled SiC MOSFETs. An in – depth analysis of the PCB layout, based on ANSYS Q3D attributed this asymmetry to the difference in source parasitic inductances of the paralleled MOSFETs. To further optimize the design that mitigates this issue significantly, a novel, multilayer copper layout strategy that takes advantage of flux cancellation between copper planes carrying currents in opposite directions is proposed, analyzed in ANSYS Q3D and experimentally validated. The proposed methodology was found to have improved the current sharing both in the dynamic and static regions of the drain current
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
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
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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