1,720,956 research outputs found
Novel Single-Stage Integrated Active Filter Isolated Matrix-Type Three-Phase AC/DC Converter (IAF-iMR)
No full textGlobal energy consumption in AI-related data centers is expected to double by 2026. This rapid growth necessitates an upgrade in their power supply architecture, where isolated three-phase (3-Φ) ac/dc converters serve as fundamental building blocks. However, state-of-the-art two-stage ac/dc-dc/dc converter concepts suffer from limited power conversion efficiency and power density. This paper proposes a novel three-phase integrated active filter isolated matrix-type rectifier (IAF-iMR) that enables high-efficiency, direct (single-stage) ac/dc conversion with high power density, while maintaining reduced modulation and control complexity compared to conventional isolated matrix-type ac/dc converters. By incorporating bipolar bidirectional switches, the proposed IAF-iMR directly converts low-frequency three-phase mains line-to-line voltages into a high-frequency switched ac voltage across the transformer's primary-side winding, eliminating one power conversion stage compared to two-stage or quasi-single-stage configurations and enhancing power conversion efficiency. The paper first explains the operating principle of the IAF-iMR using equivalent circuits, which are verified by detailed circuit simulations. Furthermore, component stresses are analyzed to guide component selection, followed by a qualitative comparative evaluation against alternative isolated three-phase ac/dc converter concepts. Finally, a novel matrix-type isolated-three-phase-HFlink three-phase ac/dc converter (i3X-Rectifier) is introduced as a next-generation high-power data center power supply solution. The proposed i3X-Rectifier employs a three-phase transformer to mitigate overstress limitations of single-phase isolation transformers, improving performance and compactness
Comparative Evaluation of Three-Phase SiC-Based Voltage/Current-Source Inverter Motor Drives
No full textVariable speed drives (VSDs) operating from a common dc bus enable significant energy savings in variable-load centrifugal systems like pumps and compressors. Ideally, VSDs should provide smooth sinusoidal motor voltages to ensure compatibility with standard motors. Thus, voltage-source inverters (VSIs) equipped with an output filter or current-source inverters (CSIs) are candidate topologies. Using multi-objective Pareto optimization, this paper provides a comprehensive comparative evaluation of VSI and CSI topology and modulation variants, which employ 1200 V and/or 900 V SiC power transistors and drive a 400 V (line-To-line rms), 7.5 kW high-speed permanent magnet synchronous machine (PMSM) with a high nominal output frequency of up to 2 kHz from a 750 V dc bus. The results indicate comparable performance of VSI and CSI topologies in terms of efficiency (weighted according to the NEMA power index load profile) and power density, yet the CSI designs require larger total chip areas at least until 900 V monolithic bidirectional power transistors become available. Advantageously, the CSI's de-side voltage-To-current conversion stage (dc-dc buck converter) can be realized with two interleaved phases that each operate in a triangular-current mode (TCM) and hence with soft-switching, while the dc-link current still shows a low ripple only; this approach clearly outperforms all other considered variants
Novel Isolated-Three-Phase-HF-Link Matrix-Type Three-Phase AC/DC Converter (i3X-Rectifier)
No full textThe rapid expansion of AI-driven data centers is significantly increasing the demand for ultra-efficient high-power three-phase (3-Φ) mains-connected single-stage ac/dc conversion solutions, featuring sinusoidal input current, galvanic isolation, and controlled output voltage. Conventional isolated-single-phase-HF-link matrix-type 3-Φ ac/dc converters encounter critical challenges at high power levels due to high component stresses. As a result, a relatively large number of low-power modules must be paralleled within a single 1 MW power rack, increasing system complexity and reducing reliability. To address this limitation, this paper introduces a novel isolated-three-phase-HF-link matriX-type three-phase ac/dc converter (i3X-Rectifier) that lowers individual component stresses and/or enhances power conversion efficiency and volumetric density in high-power, i.e., 100 kW range, data center power supplies. Utilizing a three-phase galvanic isolation transformer combined with either a direct or indirect matrix-type front-end, the proposed i3X-Rectifier enables single-stage (direct) conversion from 3-Φ low-frequency (LF) mains voltages to 3-Φ high-frequency (HF) transformer voltages, advantageously resulting in significantly reduced current stresses in main active and passive components and minimized filtering efforts. Furthermore, the proposed i3X-Rectifier supports quasi-current-dc-link operation, enabling generation of sinusoidal 3-Φ mains currents using conventional low-switching-loss current dc-link 2/3-PWM, simplifying modulation and reducing control complexity. Comprehensive closed-loop circuit simulations and comparative analyses of the proposed concept against the conventional isolated-single-phase-HF-link approach validate the substantial performance advantages of the proposed i3X-Rectifier, highlighting its suitability for next-generation high-power, high-efficiency data center power supply architectures
Ultra-Efficient Three-Phase Integrated-Active-Filter Isolated Rectifier for AI Data Center Applications
No full textAs the demand for energy in AI-driven data centers continues to rise, there is an urgent need for innovative solutions to enhance the efficiency and power density of isolated three-phase AC/DC converters. In this context, the Integrated-Active-Filter Rectifier (IAFR) emerges as a promising solution due to its low complexity and high efficiency, achieved through the low switching frequency of all power semiconductors except for an injection leg needed to shape the three-phase sinusoidal input currents. However, the IAFR's performance limits concerning efficiency and power density, as well as its behaviour under unbalanced grid conditions, are still unclear. This paper presents a detailed analysis of the IAFR operation and introduces a Triangular-Current-Mode (TCM) operation for the injection leg, ensuring Zero-VoltageSwitching (ZVS) across the entire grid cycle. Additionally, a control strategy for the IAFR is proposed to ensure sinusoidal input currents and minimize power fluctuations under unbalanced grid conditions. The proposed control and modulation strategies are verified through simulations, while a multi-objective Pareto optimization is employed to determine the performance limits of the IAFR when paired with an isolated downstream DC/DC converter stage required for galvanic isolation and output voltage regulation
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
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
- …
