1,720,958 research outputs found
Condition Health Monitoring for Medium-Voltage High-Power Modular Multilevel Converter
No full textAmong the policies to reduce the consequences of GHG emissions, the decarbonization of the electrical, transport, and manufacturing sectors has profoundly changed how the electricity is produced, transmitted, distributed, and consumed, particularly imposing several complex technical challenges to power electronics-based technologies. Future power converter solutions are called to fulfill increasingly demanding requirements of efficiency, power quality, cost, volume, and reliability, foreseeing that the next generation of high-power converters might be based on modern concepts such as the MMC.
Although the MMC exhibits extraordinary characteristics, namely, full modularity, voltage-current scalability, and high efficiency, its development is still in an early stage of maturity, and different topics such as reliability improvement are still research subjects. Around 40000 parts composing the 96 SMs used in the two MV 250kVA MMC to form the PEL MMC research platform illustrates the reasonable concern about technology reliability. CHM arises as an attractive concept to prevent failure events improving reliability and availability of power electronics-based converters. When intended for MMC, CHM development and deployment face several challenges, mainly due to the existing technique's demand for additional hardware, modification of control schemes, particular operating conditions, and complex algorithms. Consequently, MMC CHM state-of-the-art is narrowed to SM power capacitors and power semiconductors.
This thesis aims to provoke and contribute to the CHM body of knowledge by investigating three alternatives applied to the PEL MV MMC. The first is a simple, accurate, and costless online strategy to monitor the SM electrolytic capacitor's condition. The method basis on the relationship between the capacitor's degradation and capacitance level. Thus, the SM capacitance is estimated by employing measurements commonly used for necessary control and protection algorithms and the RWLS technique. RT-HIL simulations and experimental results show the method's performance under different capacitor aging levels and converter operating conditions.
A second alternative responds to the difficulties in gathering information about components other than power capacitors and power semiconductors, as cost, space, and data processing restrictions are common barriers. The strategy uses the single switch flyback-based ASPS consumption monitoring to observe simultaneously different SM sub-circuits instead of a particular component and the fault dictionary concept to detect the SM drifting from expected healthy conditions. It is demonstrated that minor and significant power consumption variations can be noticed and used for health monitoring.
Envisioned in future MMC, the handling, processing and extraction of valuable information from massive amounts of data coming from different CHM techniques is an open issue and certainly a challenge for the health assessment. Inspired by the data fusion framework and MCDM problems, a scheme to integrate various SM health indicators is proposed to compose a comprehensive health index. Systematic approaches considering objective data from the SM and subjective information from expert knowledge are presented and verified through numerical examples based on experimental data. It is demonstrated that entropy, fuzzy-TOPSIS, and game theory-based methods are superior solutions for the SM and converter-level health assessment.PE
Diseño e implementación de un controlador de potencia para la tracción y conexion V2æG de un vehículo eléctrico utilitario
Full text linkMagíster en Ciencias de la Ingeniería, Mención EléctricaLas micro redes (MR o μG) se constituyen como una solución para la electrificación mediante el aprovechamiento de los recursos energéticos renovables locales, tanto en zonas remotas como en sistemas interconectados. Sin embargo, en zonas aisladas el uso de combustibles fósil para el transporte local prevalece como un desafío a su suministro energético. Ante esta problemática, los vehículos eléctricos (VE) se perfilan como una solución en la medida que tengan la capacidad de operar coordinadamente con una MR existente en la localidad.
En esta tesis se diseña, construye y valida en laboratorio un conversor de potencia que permite el intercambio de energía entre una fuente DC y una máquina de inducción trifásica o una MR aislada, con el objetivo de materializar el concepto de V2μG (del inglés Vehicle to Micro-Grid). Se propone la utilización de un inversor trifásico, tetrapolar y multifuncional, cuyo sistema eléctrico permite dos modos de operación: el modo VE, diseñado para manipular el torque del motor de inducción trifásico del vehículo, basado en la estrategia IFOC (del inglés Indirect Field Oriented Control); y el modo V2μG, que mediante estrategias de control basadas en Acondicionadores de Potencia tipo Filtro Activo permite su integración con la MR a través de los sub-modos IDLE, COMPENSACIÓN DE COMPONENTES DE SECUENCIA CERO (CCS0), COMPENSACIÓN DE COMPONENTES DE SECUENCIA NEGATIVA (CCS-), SUAVIZADOR P-Q (SPQ) y CONTROL DE TENSIÓN BUS DC (CTBDC).
Los resultados experimentales de la operación en modo VE muestran que la estrategia IFOC implementada en el conversor funciona correctamente siempre que la medición de velocidad del rotor de la máquina sea suficientemente precisa. En este caso, se observa que la respuesta del sistema ante cambios en la referencia de tipo escalón es menor a 27[ms]. Por otro lado, en el modo V2μG, se comprueba que en el sub-modo IDLE el conversor no inyecta ni absorbe potencia de la red. Se verifica que los otros sub-modos operan correctamente y de forma independiente. Sin embargo, se obtienen mejores resultados al combinar los sub-modos CCS0, CCS- Y CTBDC, logrando reducir el THD y desbalance de corriente aguas arriba al punto de conexión desde 12,5[%] a 4[%] y de 100[%] a menos del 2[%] respectivamente. Al combinar los sub-modos CCS0, CCS-, CTBDC y SPQ se logra suavizar los escalones de potencia activa y reactiva producto de la dinámica del sistema aguas arriba del punto de conexión.
Para futuros trabajos se propone implementar una estrategia de carga de baterías, mejorar los controladores de corriente para el modo V2μG, integrar la operación en isla para cargas monofásicas y trifásicas e integrar funciones de control remoto para su operación en redes inteligentes. Finalmente, se plantea agregar la funcionalidad de dar soporte ante fallas en la red
Thermal Study of a Modular Multilevel Converter Submodule
No full textModular multilevel converters are gaining attention since medium voltage direct current grids have been proposed as the new key technology for the future transmission and distribution systems. The design of such systems need to address several challenges and this paper presents a thermal study of a modular multilevel converter full-bridge IGBT based submodule. Thorough tests have been performed under severe ambient thermal conditions and electrical stresses, typical to regular modular multilevel converter operation. Presented results demonstrate an excellent match between theoretically predicted numbers and those obtained in a custom-designed experimental test setup.PE
Estimating Auxiliary Power Supply Consumption of the Modular Multilevel Converter Submodule for the Condition Health Monitoring
No full textCondition health monitoring strategies applied to different power electronics applications are gaining popularity as early component degradation detection can trigger preventive maintenance actions before a significant fault occurs. In highly modular converter structures, such as the modular multilevel converters, made out of many submodules, the development and implementation of condition health monitoring strategies are significant and challenging. This paper analyzes and demonstrates the use of the auxiliary submodule power supply consumption to recognize submodule sub-circuits abnormal operation. Thus, a new strategy to monitor submodules components is provided, enabling new prospective condition health monitoring methods locally or at the converter level. Experimental results show the effectiveness of the proposed idea.PE
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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