1,720,961 research outputs found
Enhanced Hybrid PWM for the Closed-Loop Control of Permanent Magnet Synchronous Motor Drives
No full textIntegrating asynchronous pulsewidth modulation (PWM) and synchronous optimal PWM (SOPWM) in a hybrid PWM scheme has proven to be an effective modulation strategy for ac motor drives operating over a wide speed range. However, hybrid PWM is rarely used in permanent magnet synchronous motor (PMSM) drives in traction applications due to the noise sensitivity issues associated with SOPWM and the complex PWM transition schemes. To overcome these drawbacks, this article introduces an enhanced hybrid PWM technique suitable for integration with the well-established field-oriented control (FOC) strategy. The proposed technique relies on an innovative robust SOPWM and simple smooth PWM transition schemes to improve the robustness of hybrid PWM against noise in the control loop introduced by the measured currents and rotor position. Experimental results are provided to validate the effectiveness of the proposed hybrid PWM technique used in the closed-loop control of a PMSM drive
Torque Harmonic Minimization Optimal Pulse Pattern Modulation Technique for Permanent-Magnet Synchronous Motors
No full textPermanent-magnet synchronous motors (PMSMs) inherently exhibit torque oscillations due to their magnetic properties, impacting performance and causing increased noise and vibrations. While pulsewidth modulation (PWM) techniques commonly minimize current harmonics, they often overlook torque fluctuations arising from the interaction between current and back EMF harmonics in PMSMs. Therefore, achieving both minimal torque harmonic content and reduced switching frequency is essential to obtain a smooth torque and low switching losses. This article introduces a novel low-frequency optimal pulse pattern-based torque harmonic minimization (OPP-THM) method, designed to directly minimize torque harmonics in PMSMs, rather than solely focusing on current harmonics. By considering back EMF harmonics in the optimization of switching angles, the proposed approach effectively suppresses low-order torque harmonics without compromising the contribution of back EMF harmonics to average torque, thereby enhancing the PMSM performance. The effectiveness of the proposed method is demonstrated through validation on a 4-kW experimental PMSM drive employing field-oriented control (FOC) under steady-state and transient conditions
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
Power Electronic Transformer with Open-End Winding Electric Drive for Wind Energy Conversion Systems
Full text linkUniversity of Minnesota Ph.D. dissertation. May 2016. Major: Electrical Engineering. Advisor: Ned Mohan. 1 computer file (PDF); xii, 187 pages.Power Electronic Transformers (PETs) provide a reduction in size over line frequency transformers by operating at much higher frequencies than line frequency or grid frequency. Due to their smaller size, they could be useful in renewable energy systems where an interface with the grid is needed. As the name suggests, a power electronic interface is needed to convert line frequency voltages to high frequency voltages before they can be fed to the transformer. A PET topology that has simple control and less number of high voltage devices would be considered desirable due to lower total device cost and easy control implementation. A push-pull based PET topology has been proposed in the past which contains only two high voltage controlled switching devices and the control of those two devices is very simple. This topology could be configured for single stage ac to dc power conversion, to which an open-end winding dc to ac converter could be connected. Alternatively, it could be configured for direct ac to ac power conversion using dual matrix converters. In the first part of this thesis, the aforementioned push-pull based power electronic topology has been studied for power conversion from ac to dc and vice versa. Both single phase ac to dc and three phase ac to dc variants of the topology have been analyzed for power transfer, rms currents and soft switching. They provide attractive features which include single stage ac to dc bidirectional power conversion, unity power factor operation in open loop and control of dc side voltage using simple PI controllers. The other part of this thesis deals with open-end winding drives for suppression of common mode voltages at machine terminals. Switching frequency Common Mode Voltages (CMV) are generated by conventional Pulse Width Modulated (PWM) drives at machine terminals, which cause shaft voltage build up leading to bearing currents. These bearing currents are harmful for the machine and also cause Electromagnetic Interference (EMI). Open-end winding drives consist of one electric drive connected on each end of a three phase electric motor with the stator neutral opened up to give three more terminals. Open-end winding drives can be controlled to suppress switching frequency CMV at machine terminals. In this thesis, open-end winding two level Voltage Source Inverter (VSI) drive and open-end winding two level Matrix Converter (MC) drives have been investigated. Carrier based PWM techniques have been proposed for each of these drives for suppressing CMV. In addition, an improved four step commutation method has been proposed for the open-end winding matrix converter drive to suppress CMV spikes during the commutation process. Finally, a circuit consisting of the reduced switch PET connected with an open-end winding MC drive has been studied for single stage ac to ac power conversion with open loop power factor control.Baranwal, Rohit. (2016). Power Electronic Transformer with Open-End Winding Electric Drive for Wind Energy Conversion Systems. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/198995
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
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
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