1,720,959 research outputs found
Performance analysis of envelope modelling applied to resonant converters
Full text linkResonant converters are often studied using their envelope models, i.e. the transfer functions that relate the envelope of the output quantities to those of the input ones. Transfer functions can accurately represent only the input-output relation of linear systems and hence any method used to develop the envelope model cannot be accurate if the resonant converter processes the envelopes in a non-linear way. This paper works out a general criterion that recognizes whether the envelope processing is linear or not, the type of the eventual non-linearity and its amount. The criterion is expressed in terms of conditions that have to be fulfilled by the input-output Bode diagram of the converter. These conditions are of general validity and do not depend on the converter topology; their applicability is not limited to resonant converters, but it can be extended to any system. The conditions have been derived by reviewing the procedure that leads to the Modulated Variables Laplace Transform method for the development of the envelope models. The theoretical results are verified at first by simulations and then by experimental tests carried out on two different resonant topologies of a prototypal converter that works as wireless battery charger
Modified Series-Series Compensation Topology for WPT Systems
No full textWireless Power Transfer Systems use a wide selection of different compensation topologies to enhance one or the other of their characteristics. Among the simplest topologies, the series-series compensation offers high efficiency in a wide range of transferred power but requires an effective control of the output voltage and of the supply current when used in applications where the load varies substantially in order to protect the system from overvoltage or overcurrent. This paper presents a modified series-series compensation topology that inherently implements this protection at the expenses of a small decrease of the transfer efficiency. At high loads, the modified series-series topology operates as the conventional one, but at low loads its behavior changes limiting the transmitting side current and the output voltage. A preliminary analysis of operations of the proposed topology is performed in the time domain, then it is completed in the phasor domain and, finally, the obtained results are checked against those obtained by simulation implemented in the PSIM environment
Dynamic EV Charging WPT System Control Based on Modulated Variable Laplace Transform
No full textThe paper deals with the control of an LCL-compensated WPT system (WPTS) for the dynamic charging of electric vehicles (EVs). As it is well-known, the high working frequency of the WPTSs prevents their instantaneous control because of the fast processing that would be required for the controlled quantities, well beyond the capabilities of the modern microcomputers. Therefore, the control of the WPTSs is carried out by acting on the envelopes of the controlled quantities on account of the fact that they have a sinusoidal waveform. In this paper, the controlled quantities selected for the considered WPTS are the transmitting coil current and the DC-bus voltage at the receiving stage, and the input quantity is the supply inverter voltage. The transfer functions (TFs) between their envelopes are at first computed by means of the Modulated Variable Laplace Transform method. Then, the controllers of the WPTS control system are designed by help of the computed TFs. At last, the performance of the arranged control system is tested by simulation
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
An Analysis‐Supported Design of a Single Active Bridge (SAB) Converter
Full text linkCurrently, due to its various applications, the high‐performance isolated dc‐dc converter is in demand. In applications where unidirectional power transfer is required, the single active bridge (SAB) is the most suitable one due to its simplicity and ease of control. The general schematic of the SAB converter consists of an active bridge and a passive bridge, which are connected through a high‐frequency transformer thus isolated. The paper summarizes the behavior of this converter in its three operation modes, namely the continuous, discontinuous, and boundary modes. Later, the features of this converter, such as its input‐to‐output and external characteristics are discussed. Input‐to‐output characteristics include the variation of converter output power, voltage, and current with an input control variable i.e., phase‐shift angle, whereas the external characteristic is the variation of the output voltage as a function of output current. In this discussion, the behavior of this converter in its extreme operating conditions is also examined. The features of the characteristics are elucidated with the help of suitable plots obtained in the MATLAB environment. Afterward, the specifications of a SAB converter are given and, based on the results of the analysis, a detailed design of its electrical elements is carried out. To validate the features and the design procedures presented in this paper, a prototype is developed. An element‐wise loss estimation is also carried out and the efficiency of the converter has been found to be approximately equal to 93%. Lastly, the test was executed on this prototype, confirming the theoretical findings concerning this converter
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