1,720,960 research outputs found
Fast Simulator for the Estimation of Inverter DC-link Temperature in e-Drives Subjected to Highly Variable Working Cycles
No full textAccurate estimation of losses and operating temperatures is extremely important for the design of traction inverters and its validation for specific operating conditions. Although several methods are already available in the literature to estimate the semiconductor power losses, the power losses and temperature evaluation of inverter DC-link capacitors are less explored. Therefore, this paper presents a fast simulation model of traction eDrive to provide accurate estimation of DC-link loss and temeperature, as well as DC link voltage ripple evaluation. The proposed model is implemented in Simulink and consists of both a loss model based on loss maps and a circuital model to estimate the dc-link voltage ripple. This model is very fast and therefore it is very useful when the eDrive is subject to long and highly variable driving cycles. Moreover, the model accounts for the influence of the main parts of the powertrain and allows a proper verification of the selected DC link capacitor
Fast Overcurrent Protection for Direct Drive Cascode GaN HEMT Semiconductors Based on Industrial Gate Drivers
Full text linkGallium nitride high electron mobility transistors exhibit excellent switching and conduction performance. However, their adoption in safety-critical applications is subject to concerns about their capability to withstand severe overcurrents. Therefore, fast and reliable overcurrent protections are needed to guarantee the safe operation of the power switches. The conventional desaturation protection methods, widely used for MOSFETs and IGBTs, do not match with the reduced shortcircuit capability of new GaN HEMTs semiconductors. To address this issue, this paper proposes a fast overcurrent protection scheme specifically designed for direct drive cascode GaN HEMT. The proposed solution uses an industrial gate driver along with a few additional components, leveraging the measurement of the conduction voltage of the cascode MOSFET as an indirect indicator of the device current with very good precision and reduced intervention time. The effectiveness of the proposed overcurrent protection scheme is supported by experimental results
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
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
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
Design of a 75kW Three-Level DC/DC GaN Converter for Automotive Fuel-cell Application
No full textNowadays, fuel cells represent a promising alternative to replace battery packs for electric vehicles where weight is a concern or where electrical charging is not possible. With respect to a battery pack, built up to 800V, the output voltage of fuel cell stacks is rather low (typically below 200V) and also it is strongly dependent on the load current. Therefore, the integration of a fuel cell in an electrical powertrain needs a DC-DC converter that must exhibit high efficiency and power density. Therefore, this paper presents the design and optimization of a 75 kW, multi-level DC-DC converter leveraging the benefits of the gallium-nitride (GaN) power devices and on the ceramic technology for the capacitors. The paper presents results regarding the GaN device selection with loss analysis, the DC link capacitor sizing and the design of magnetic components. The estimated power density of the converter is 41.7kW/L with a 99.1% overall maximum efficiency
Digital Control of a Multilevel Interleaved DC-DC GaN Converter for Fuel Cell Traction Applications
No full textNowadays, fuel cells represent a promising alternative to replace battery packs for electric vehicles where weight or the limited range is a concern. With respect to a battery pack, built up to 800 V, the output voltage of fuel cell stacks is rather low (typically below 200 V) and it is strongly dependent on the load current. Therefore, the integration of a fuel cell in an electrical powertrain needs a DC-DC converter. To maximize the power density, the gallium-nitride (GaN) technology represents an interesting solution as it allows unprecedented performance in terms of switching frequency. As the rated voltage of available GaN devices is limited to 650 V, multilevel solutions must be employed for DC-DC converters whose output is 800 V. As the switching frequencies are usually above 100 kHz, the control of such converters is challenging, especially when multiple interleaved switching cells must be controlled. The literature reports several publications focusing on the adopted topologies for DC-DC conversion, while few papers deal with the digital control of such multilevel DC-DC converters. Therefore, the goal of this paper is the digital control applied to a high-power multilevel interleaved GaN DC-DC converter for an electrical powertrain fed by fuel cell
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
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