1,721,836 research outputs found
Integration of stationary batteries for fast charge EV charging stations
Full text linkOne of the biggest issues preventing the spread of electric vehicles is the difficulty in supporting distributed fast charging stations by actual distribution grids. Indeed, a significant amount of power is required for fast charging, especially if multiple vehicles must be supplied simultaneously. A possible solution to mitigate this problem is the installation of auxiliary batteries in the charging station to support the grid during high peak power demands. Nevertheless, the integration of high-voltage batteries with significant power is not a trivial task. This paper proposes the configuration and control of a converter to integrate batteries in a fast charging station. The proposed configuration makes it possible to decouple the grid power from the vehicle power using several auxiliary battery modules. At the same time, the converter makes it possible to draw different amounts of power from the battery modules, allowing the use of second life batteries performing in different ways. This paper discusses the design, control, and operation of the converter. Moreover, the effectiveness of the proposed control is shown by means of numerical results
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
A Novel Approach for Distributed Maximum Power Point Tracking Using Modular Multilevel Converters
No full textThis paper deals with the problems of grid connected PV-farm configurations due to partial shading effect and mismatch operation of PV panels. One proposed solution in literature is distributed maximum power point tracking (DMPPT) technique. The benefits of this technique in comparison to other conventional centralized PV-farm configurations are well known and already discussed in the technical literature. In this paper converter topology, integrating the PV modules, for DMPPT technique is proposed. The converter topology and the proposed control technique has been tested by means of numerical simulations in Matlab-Simulink environment. The results demonstrate that the controller is able to follow the maximum power point of each PV module, while injecting balanced currents to the grid even in cases of inhomogeneous irradiation
Simple control strategy for a PV-battery system
No full textNowadays, energy storage systems, such as batteries, are spreading in many applications. Among the kinds of batteries, the lithium-ion technology is one of the most promising solutions. Considering the photovoltaic (PV) plants, it is very important to perform a correct sizing of the battery pack to both maximise the self-consumption and minimise the total costs. In general, PV plants need a dc-dc converter to maximise the electric power that can be extracted from PV panels and a dc-ac converter to connect them to the ac grid. The battery pack can be connected in three different ways: dc coupled and ac coupled using a dedicated converter or through a direct connection on the dc-link between the dc-dc and dc-ac converters. In the present study, the last solution, without any dedicated converters, is used and a simple control strategy to both maximise the power extracted from the PV panel and regulate the charging/discharging of the battery is proposed
Optimization of MMC level number for battery integration in MV grid
No full textThe integration of battery energy storage systems in electrical grids is one of the most interesting challenges of the recent years. In this regard, one potential solution is based on a modular multilevel converter (MMC) with batteries directly embedded at each submodule level. This solution allows to reach medium voltage level using low voltage devices avoiding the necessity of complex battery management system to balance the high voltage battery modules. Several studies have been performed on MMC topologies to integrate storages. Nevertheless, there are not dedicated studies to analyse the effect of the number of levels on efficiency and cost of the final solution. This paper focuses on the efficiency evaluation and on the cost analysis of the MMC combined with energy storage systems. After evaluating the total power losses of the converter, the efficiency for different number of submodules is analysed. In addition, cost comparison between different solutions, taking into account several factors such as component price, converter power losses cost and operational & maintenance cost, is discussed
Control strategy to improve EV range by exploiting hybrid storage units
Full text linkIn the past, the diffusion of electric vehicles (EVs) has been hindered by energy storage limits. In fact, these are the reason for the limited EV range and the consequent range anxiety of their drivers. Thanks to constant improvements in storage system technologies over the years, in terms of both energy and power density, lithium-ion batteries (LiBs) now guarantee vehicle ranges higher than 150 km for small vehicles. Another important improvement has been achieved by the hybridisation of LiBs with other storage technologies such as electric double-layer capacitors or lithium-ion capacitors. By adding an additional storage unit (ASU) to the EV battery system, the overall efficiency increases, with a consequent gain in the vehicle's expected range. In a previous paper, an optimal sizing procedure was proposed, through which it is possible to calculate the optimal ASU mass that maximises the EV range for a given vehicle, ambient conditions, and driving cycle, which was considered to be known a priori. In the present work, a real-time implementation of the control strategy on which the optimal sizing procedure was based is proposed and analysed using the results of simulation tests
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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