1,720,968 research outputs found
Experimental and numerical study of the recovery softness and overvoltage dependance on p-i-n diode design
No full textThis work offers a reliability-oriented characterization of power p–i–n diodes turn-off transients. The softness of the turn-off and the snap-off voltage (defined as the threshold beyond which large, anomalous reverse overvoltages develop across the diode at turn-off) are investigated both experimentally and numerically for a wide set of diodes with different drift region width, resistivity and lifetime. In particular, lifetime control is obtained by electron irradiation at different doses. As a result, guidelines emerge for the design of the snubberless diode with optimum trade-off between switching speed and softness. It is also suggested that, for complete diode characterization, the well-known softness factor be accompanied by the snap-off voltage, i.e. the peak reverse voltage triggering anomalous oscillations in the turn-off transient
A software tool for thermal simulation and rating evaluation of high power silicon devices
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
A Reduced-Sensor Modular Dual Active Bridge-Based Battery Charging System for Electric Vehicles Using an Improved Linear Extended State Observer
No full textDeveloping an off-board rapid battery charging station is quite challenging since it must handle numerous battery chemistries with varying power requirements while maintaining high power conversion efficiency and small size. Furthermore, numerous modular topologies are widely employed to meet the battery's high power requirements while decreasing voltage and current stress on power switches, permitting the use of low-power rating switches. In such modular architectures, power balance among modules must be ensured to avoid overvoltage/overcurrent. Furthermore, such modular systems require many sensors, raising system costs. The traditional observers commonly used to reduce the sensor number introduce large errors between the actual and estimated system states and possess poor transient performance. To address these shortcomings, this paper proposes an improved extended state observer for modular DAB-based battery charging of electric vehicles. Numerical simulations using MATLAB/Simulink demonstrate the proposed system's robustness against disturbances and show how the transient response of the system is greatly improved
Variations on the Author
Full text link“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
Thermo-mechanical finite element analysis in press-pack IGBT design
No full textThe reliability of press-packed insulated gate bipolar transistors (IGBTs) depends on satisfactory contact conditions applied at assembly stage and maintained throughout the service life. The objective of this work is the simulation of stresses and strains in press-packed IGBTs due to assembly and thermal cycling. Single-chip as well as multi-chip devices were analyzed with 2D and 3D models including an elastic-plastic material description and the contact between components using the ABAQUS code. The assembly process was initially modeled and the factors affecting the contact pressure uniformity between contact disks and chip discussed. The thermal cycling associated with accelerated stress test was then introduced to examine contact pressure evolution as well as local stress/strain concentrations and stick/slip conditions. The device sensitivity to potential damage initiation due to thermo-mechanical fatigue and/or fretting is addressed. © 2000 Elsevier Science Ltd. All rights reserved
Finite Element Design of Water Heat Sinks for Press-Pack IGBTs
No full textIn the power electronics market the keywords for an evaluation of fluid heat sinks are "pressure drop" and "thermal resistance". Nevertheless the devices that have to be cooled, especially the chips contained in the presspack IGBTs, require a uniform distribution of the surface temperatures in order to withstand a large number of thermal cycles. For this reason the commonplace concept of "thermal resistance" that does not take into consideration the non-uniformities cannot be satisfactory. In this work, because of its complexity, we don't present any new project solutions nor any new prototypes. On the contrary our aim is to show the importance of a complete 3D modeling as a support in the modem designing of fluid heat sinks in order to produce really efficient products
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
High reliable high power diode for welding applications
No full textLong-term power cycling of high power diodes for welding application is presented. The devices are packaged in an ultra-slim flat package, which allows very high heat sinking capability and rating current. Tests with different operating conditions were carried out and the results compared with the few data available in literature. Our devices show very good lifetime, especially considering that all tests were terminated without any performance degradation. Finally a thermo-electrical model of the device was built and will be used for both validation of lumped element thermal models and evaluation of new design solutions
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