1,720,955 research outputs found
A scheme for the power control in a DFIG connected to a DC bus via a diode rectifier
Full text linkThis paper deals with a new conversion topology for doubly-fed induction generators (DFIGs) suitable for wind energy conversion systems integrated in microgrids. It consists of a DFIG which is fed by a pulse width modulation converter on the rotor and with the stator connected to a dc grid through a diode rectifier. In this configuration, the stator diode rectifier and the rotor-side inverter share the same dc bus, so that the conventional grid-side inverter is avoided. Since only a diode rectifier designed for the full power and a reduced power inverter are required, this layout allows a cheap and effective integration of the DFIG with other generating and storage systems connected to the same dc bus. A simple control technique suitable to regulate the power delivered to the dc grid is proposed. The scheme is based on the regulation of the amplitude of a suited fraction of the rotor flux linkage: the optimal value of this fraction is theoretically deduced in order to minimize the DFIG derating due to the current harmonics. The effectiveness of the proposed control is proven by simulations and experimental tests
An Explicit Minimum-Loss Control Strategy for Dual VSI DFIG-DC Systems
Full text linkThis article presents a new minimum-loss control strategy for vector-controlled dual-voltage source inverter (VSI) doubly-fed induction generator (DFIG)-dc systems. The optimization is based on a simplified formalism using Lagrange multipliers to determine the optimal stator frequency, stator/rotor magnetizing current split, and the magnetizing flux magnitude as a function of the machine operating conditions, namely speed and torque. Compared with existing minimum-loss control schemes, the proposed approach provides an explicit solution for all three optimal quantities, which makes the implementation and control design easier, thus avoiding the use of an additional proportional–integral (PI) controller to solve the flux implicit optimality condition. The theoretical framework also includes a sensitivity analysis against DFIG parameter variations, to appraise the robustness of the proposed control scheme. The devised approach and related control implementation scheme are validated with the simulation and experimental results
Torque Ripple Reduction in a DFIG-DC System by Resonant Current Controllers
Full text linkA DFIG connected to a dc bus by a diode rectifier and a unique reduced-power PWM converter is considered in this paper. With respect to the traditional ac-grid connected DFIG, such a layout avoids the presence of the grid-side PWM converter and is an interesting solution to integrate the DFIG in a dc micro-grid together with other generating units, loads as well as storages. The peculiarity of the DFIG, which allows the control of the rotor current space vector independently of the mechanical position, offers two important benefits when the stator is connected to a constant voltage dc grid by a diode bridge: it avoids the need to boost the flux amplitude at low speed, and it allows to considerably reduce the torque ripple due to the diode commutation. This last issue is developed in the present paper by using a field oriented control scheme based on Proportional-Integral and Resonant Controllers. The proposed control is validated through simulation and experiments
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
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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