1,720,957 research outputs found
Analysis and experimentation of a novel modulation technique for a dual-output WPT inverter
Full text linkDynamic wireless power transfer systems require to supply many transmitting coils deployed under the road surface and arranged along the so-called track. This layout entails the use of a large number of inverters or of devices that switch the power to the proper coils. This paper presents a technique that uses a single three phase inverter to supply two coils with voltages having different and independently adjustable amplitudes of their first harmonic component. Differently from the well-known phase shift technique, the amplitude and the phase of the voltages are not correlated. Moreover, the presented technique has the ability of inherently reducing the phase difference between the two output currents when the supplied loads are partially reactive. This feature enhances the power transfer capability of the inverter when both the track coils are coupled with the same pickup. After presenting this technique, the paper analyzes the functioning of the dual-output inverter in different load conditions recognizing the boundaries of four different modes of operation. For each of them the analytical expression of the amplitude and phase of the generated voltages are given. The theoretical findings are validated by experiments performed on a prototypal setup that implements the presented modulation technique
Avoiding Null Power Point in DD coils
No full textDD coils are one of the most used coupling arrangements for the tracks and the pickups in dynamic wireless power transfer system. They reach a higher coupling coefficient with respect to conventional coil pairs with the same dimensions and assure a more effective and efficient power transfer to the electric vehicles. On the other hand, DD coils suffer of the phenomenon known as null power point, by which the power transferred to the pickup, is zero even if it is still partially coupled to the transmitting track coil. The null power points are typically removed by installing the so-called Q coil in the pickup. The power transferred to the Q coils is added to that harvested by the DD coil by a separate power converter so that the overall architecture of the receiving side of the dynamic wireless power transfer system results rather intricate. This paper presents a different approach to the problem of the null power points, based on the switching between two different supplying modes of the track DD coils. In front of a more complex architecture of the power supply system of the track, this approach gets rid of the Q coil and of the relevant power converter. The proposed solution is at first studied analytically with an approximated model of the DD coils and then verified by means of a FEM analysis and simulation
Dual-output inverter with phase correction ability for dynamic WPT track supply
Full text linkDynamic WPT systems are extensively investigated as a promising solution to the issues of the comparatively short range and long recharge time of the electric vehicles. In dynamic WPT systems, the lumped tracks exhibit greater power transfer efficiency than the stretched ones but require the supply of a large number of transmitting coils. This paper proposes a command strategy for a dual-output inverter that allows the concurrent supply of two track coils, with the ability of adjusting independently the voltage applied to each of them without altering the phase relation between the two supply currents. Moreover, if the series resonant compensation is used at the track side, the proposed strategy is robust against the onset of a reactive component in the loads seen at the inverter outputs as it inherently corrects the phase of the coil currents without making recourse to any additional control algorithm
Dual mode supply system for DD coils
Full text linkDD coils are often selected as case study for the research activity about the dynamic wireless charging systems for electric vehicles and are proposed to setup the track and/or the pickup onboard the vehicles. Indeed, they offer good coupling performance, but their capability can be fully exploited only if both the track coil and the pickup have the same DD topology, otherwise the transferred power decreases substantially. This paper proposes to use a three-legs inverter to separately supply the two sub coils that form a DD coil. Adopting a suitable control strategy of the inverter, the dynamic wireless charging system is made able to perform an effective power transfer both to DD coil pickups and to spiral coil pickups. Condition under which this result is achieved and the required modifications of the supply system and of the coils are studied in the paper. The proposed solution is validated by means of simulations
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
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
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