1,720,996 research outputs found
Multilevel Gate Driver with Adjustable Gate Voltage for Thermal Stress Reduction of Power Switches in Electric Drive Application
No full textDue to varying load currents, the junction temperature variations of power switches causes thermal stress and compromises lifetime. In this paper, proper gate voltage control is used for all power switches in a three-phase electric drive to smooth the profile of conduction losses, therefore reducing thermal stress. A multilevel gate driver with an adjustable gate voltage is introduced for experimental verification of the thermal control method. The lifetime is estimated at last, which indicates an improvement by a factor of two
Thermal Stress Reduction and Lifetime Improvement of Power Switches with Dynamic Gate Driving Strategy
No full textThe thermal stress and lifetime of semiconductor power switches are largely influenced by its current flow profile. Considerable thermal stress and reduced lifetime problems occur especially at low frequency operation. In this paper, a dynamic gate driver that supplies adjustable voltage is proposed to mitigate thermal stress for lifetime improvement
A modular high-voltage pulse generator based on transformer charging with high boosting capability and low-voltage dc input
No full textBy applying repetitive and high-voltage pulses across a specific medium like a reactor or a chamber, a transient plasma is generated which can be used for various applications including water treatment, air purification, and food sterilization. In order to generate the aforementioned pulses, in this paper, a modular high-voltage pulse generator (HVPG) based on cascaded full-bridge sub-modules (FB-SMs) and transformer-based charging is proposed. By utilizing transformer-based charging, the need for a complex balancing circuit with numerous sensors is eliminated and all capacitors are charged incessantly via an uninterruptible charging circuit. The proposed topology has a high boosting gain and is able to charge all capacitors from a low-voltage dc input through the use of an inverter, transformer network, and voltage multiplier circuits. The FB-SMs can provide bipolar and variable voltage pulses, as well as modularity, both benefiting the efficient and cost-effective generation of plasma.The operation principle and the modulation strategy of the proposed HVPG is analyzed and verified by the simulation results using PLECS software
Comparative study of two analytical methods for calculating the parasitic capacitance in toroidal transformers
Get PDFTransformers are of paramount importance in the implementation of different power converters such as pulsed power generators and switched-mode power supplies. The role of the transformer network is becoming even more prominent in applications that use networks of transformers or multi-winding configurations, such as series-connected transformers in pulsed power generators to provide several isolated voltages. Recently, toroidal cores have gained more popularity owing to offering compact size, less weight, and less leakage inductance due to the absence of gaps in their structure. However, their parasitic capacitance can adversely influence the performance of the power converters due to the resulting electromagnetic interference (EMI). Therefore, the parasitic capacitance of the transformer is a decisive factor in the system performance and it should be targeted to allow performance boosting. In this paper, the parasitic capacitance of transformers is modeled based on two different analytical methods. In addition, an accurate function is proposed to calculate effective parasitic capacitances considering all capacitive couplings, including turn-to-turn and turn-to-core capacitors. Afterward, these two methods are verified by planar, axisymmetric, and 3-D finite-element simulations via FEMM and COMSOL Multiphysics software, respectively. Finally, different analyses and simulations are compared with experimental results
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
- …
