1,720,978 research outputs found
Flexible synchronous PWM control of cascaded inverters for photovoltaic generation
No full textDevelopment of the modulation strategy for synchronous control of cascaded inverters, supplied by two strings of photovoltaic panels and connected to a grid by a three-phase transformer with an open winding configuration on primary side, has been done in the paper. Algorithms of synchronized pulse width modulation (PWM) are based in this case on continuous control of switching frequencies of two inverters as function of magnitudes of the DC-links voltage. It allows providing both continuous voltage synchronization in each inverter and in the load, and also an improvement of effectiveness of operation of the systems under some operating conditions. Spectral assessment of quality of the phase voltage for the systems with basic versions of synchronized PWM has been performed
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
Algorithms of Overmodulation Regulation of Neutral Clamped Inverters for Photovoltaics
Full text linkThis manuscript presents results of study and research of synchronous adjustment in the overmodulation control zone of three neutral-clamped inverters (NCIs) of the specific configuration of three-phase grid-connected photovoltaic system. It has been proved, that the corresponding modification of techniques and algorithms of pulsewidth modulation (PWM) for control of NCIs, assure symmetry and advanced harmonic composition of inverter-side winding voltage of multi-winding power transformer, thereby helping to reduce losses in windings of the transformer, and to improve the efficiency of photovoltaic installations
Flexible synchronous regulation of power electronic blocks of transformer-based photovoltaic stations
Full text linkOnly AbstractPhotovoltaic (PV) systems are very popular sources of renewable electrical energy. Voltage source inverters (VSI) are the main workhorses of PV installations, providing controlled conversion of dc voltage from PV strings into the required ac voltage for energy consumers. To ensure synchronization and symmetry of basic voltages of PV inverters at increased power levels, an original strategy and scheme of synchronous modulation have been developed for regulation of inverters of some promising structures of systems
FLEXIBLE SYNCHRONOUS REGULATION OF POWER ELECTRONIC BLOCKS OF TRANSFORMER-BASED PHOTOVOLTAIC STATIONS
Full text linkThe paper presents the results of developing a scheme for synchronous pulse-width modulation (PWM) of signals in dual voltage source diode-clamped inverters (VSDCIs) used in grid-tied, transformer-based photovoltaic (PV) stations. This scheme is based on the continuous regulation of the switching frequency of the inverters relative to the magnitude of the DC voltages of the PV strings, ensuring equivalence of switching losses across each inverter. The proposed control and PWM techniques ensure the elimination of even-order harmonics and subharmonics in spectra of voltage at inverter-side windings of power transformer, helping to increase the operating efficiency of inverter-based PV stations. Simulation results showed a behavior of operation of dual-VSDCI-based PV installations with the proposed control strategy
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