1,720,957 research outputs found
Investigation of Controlled Fault Interruption Strategies in Isolated MV Distribution Systems
No full textThe paper presents an investigation of the applicability of controlled fault interruption techniques in radial, isolated, medium voltage distribution networks. In particular, when single phase-to-earth faults occur in isolated distribution systems, it is necessary to mitigate switching overvoltages. A comprehensive set of simulations has been carried out to evaluate the sensitivity of overvoltage phenomena to different switching strategies, with the aim of highlighting the possible methods to mitigate them and, thus, avoid harmful effects on electrical systems. The presented results show slight benefits in reducing overvoltages in the primary substation by independently controlling each pole of the switching device, regardless of the considered switching strategy. The inherent limitations of this approach are hence discussed, highlighting the current technological limitations, and alternative mitigation strategies are suggested
Intelligent control based on single-input interval type-2 fuzzy iPI and super twisting nonlinear sliding mode compensator for regulating PEMFC output voltage
No full textThe control of Proton Exchange Membrane Fuel Cell (PEMFC) is exceptionally challenging due to its complex nonlinearity, slow dynamics and load disturbance. In this paper, an Adaptive Model Free Control (AMFC) approach is introduced for regulating the PEMFC output voltage under load perturbation and measurement noise conditions. The proposed method consists of four sub -elements. Firstly, an Extended State Observer (ESO) based on a Single -Input Interval Type -2 Fuzzy intelligent PI (SI-IT-2-FLC-iPI) scheme is designed to enhance the performance of PEMFC. Secondly, a Nonlinear Sliding Mode Control -based Super Twisting Algorithm (NSMC-STA) is used as an auxiliary control approach to reduce the estimation error and ameliorate the system robustness. Thirdly, a Forgotten Recursive Least Square Error (FRLSE) is applied for adjusting the physical parameter of MFC and further ameliorating the control response. Finally, all these elements are merged together within what it is called Ultra Local Model (ULM). Through extensive simulation, the efficacy of the proposed regulator in accurately tracking the output signal is showcased, outperforming conventional controllers with remarkable improvements. The system achieves 0.001 steady-state error, 0% overshoot and settling time of approximately 8.9 s, which is good enough in the context of standalone fuel cell applications
Voltage Tracking of PV with a Nonlinear Controller in DC Microgrid: An Experimental Verification Using Hardware-in-the-Loop
Get PDFThe Photovoltaic (PV) energy conversion is susceptible to fluctuations determined by the operating point of the cells employed. These variations in the output voltage impact the overall efficiency of the array when directly linked to the load. In this paper, the authors focus on a system that seamlessly integrates a renewable energy source, precisely a PV source, with the power system through a Non-Inverting Buck-Boost converter. To control the voltage, a sliding mode-based nonlinear controller has been implemented to track the photovoltaic source at different power points. The proposed control strategy allows for fulfilling the voltage regulation requirements defined by the user from a SCADA in real-time. The proposed nonlinear controller has been modelled on Typhoon Hardware-in-the-Loop (HIL) Schematic Editor (2023) and simulated on Typhoon HIL SCADA (2023) to verify the performance of the designed framework. The results obtained from diverse simulation scenarios are presented, providing insights into the overall performance of the proposed system
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Protezione, riconfigurazione automatica e monitoraggio di un sistema di distribuzione ad anello in media tensione
No full textLAUREA MAGISTRALEQuesta tesi descrive la progettazione del sistema di protezione, di controllo e di monitoraggio della rete di distribuzione di un Ospedale. La rete è strutturata con una topologia ad anello costituita da cabine elettriche di media tensione, quadri di distribuzione, apparecchiature di manovra, relè di protezione, trasformatori, sensori di tensione e corrente, gruppi elettrogeni di emergenza etc. L’impianto è esercito in anello aperto.
Il sistema progettato include: unità di protezione con specifiche curve di intervento tempo-corrente; un sistema di interblocco per l’implementazione della selettività logica, di interventi per trascinamento e altre funzioni avanzate di protezione; un sistema di automazione, basata su un controllore a logica programmabile, che gestisce la riconfigurazione della rete; un sistema di comunicazione, basato su collegamenti Ethernet e in fibra ottica, per mezzo del quale si costituisce l’infrastruttura per i segnali di interblocco logico e per i dati di monitoraggio; un sistema di supervisione costituito da un’interfaccia grafica ad uso di un operatore.
La tesi descrive la progettazione degli elementi elencati e definisce nel dettaglio le procedure di collaudo effettuate su ognuno di essi prima della messa in servizio dell’impianto.This thesis describes the design of a protection, control and supervision system for the Medium Voltage power distribution grid of a Hospital. The network is structured as a ring with stations, switchboards, switchgears, relays, power transformers, emergency power-supplies, etc. Network is operated as an open ring.
The designed system includes: protection units with individual time-current curves; interlock system to implement logic selectivity, intertripping and other advanced protection functions; automation, based on programmable logic controllers, which operates network reconfiguration; communication system, based on Ethernet and on optic fiber segments, which serves as the transport infrastructure for interlock signals and monitoring data; supervision system with graphical operator interface.
The thesis describes the design of each of the above elements, and details the testing procedures enacted on each of them before putting into operation
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
Get PDFWe 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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