Design optimization of switching-cell-array-based power converters

© 2022 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.With the aim to increase standardization, reduce the cost, and obtain advanced performance features, the design of voltage-source power converter legs can be undertaken by combining several instances of a standard switching cell, properly connected in active neutral-point-clamped structures to reach the desired voltage and current ratings. These switching cells can be organized into switching-cell arrays. This design approach introduces several degrees of freedom into the design. Namely, the different options to interconnect the cells and the distribution of switching losses among these cells. This article aims to define an optimization problem to explore this design space. The design problem is formulated in different scenarios, involving different conversion configurations (dc-dc and dc-ac), different leg number of levels (two and three), and different types of available cells (standard and conduction-optimized in combination with switching-optimized). A weighted objective function is then defined in terms of leg simplicity, efficiency, and reliability. The value of the design variables that minimize the objective function with different sets of weighting factors are obtained under selected scenarios and operating conditions, to illustrate the flexibility of the converter design approach under study. The solution of the optimization problem is obtained using a surrogate optimization algorithm in MATLAB, well suited to quickly solve optimization problems involving a combination of integer design variables (the number of parallel switching cells in each converter leg position) and continuous design variables (the proportion of switching losses taken by each cell), together with linear and nonlinear constraints.Postprint (author's final draft

Castillo de El Cuerno (Fuentes de León, Badajoz): its late antique phase and the location of a worship area dated to the visigothic period

Durante las excavaciones arqueológicas llevadas a cabo en el castillo de El Cuerno (Fuentes de León, Badajoz) se pudo documentar una mezquita que fue construida con materiales reutilizados. Algunos de esos materiales indicarían claramente la existencia de una importante fase tardoantigua, con un edificio de culto dedicado a San Vicente que debió de ser derribado para construir la mezquita. La singularidad de los materiales también aporta datos sobre los contactos entre al-Ándalus y los reinos del norte en la Alta Edad Media.The archaeological excavations carried out in the Castillo de El Cuerno (Fuentes de León, Badajoz) enabled the identification of a mosque built with recycled materials. Some of these materials point at the existence of an important late antique stage, as there was a place of worship to Saint Vincent that was demolished in order to erect the mosque. The uniqueness of the materials also provides information about the contacts between Al-Andalus and the kingdoms in the North during the High Middle Ages.Ministerio de Economía y Competitividad FFI2012-39395-C02-01 HAR2012-36963-C05-0

Monseñor Romero: nuestra voz, nuestra luz

Nota editorial. A través del no resuelto problema de la restauración de la verdad, la justicia y la reparación integral de las víctimas, luego de los Acuerdos de Paz en 1992, en El Salvador ha quedado un vacío tanto de justicia como de rescate de la memoria histórica con el objetivo de lograr una compensación lo más completa posible a las víctimas desaparecidas, muertas o sobrevivientes, de la guerra fraticida que azotó el país entre 1980-1992 como a sus familiares. La tesis central del ensayo se centra en la figura de Monseñor Romero y su praxis religiosa, el de una opción preferencial por los pobres que, una vez consumado su martirio, sigue presente en el inconsciente colectivo del país a través de su ejemplo. Se trata de una voz que acompañó a su pueblo como de una luz que ilumina su camino.Editorial note. Through the unresolved problem of the restoration of truth, justice and the integral reparation of the victims, after the Peace Accords in 1992, in El Salvador there has been a vacuum both of justice and of the rescue of historical memory with the objective of obtaining the most complete compensation possible for the disappeared, dead or surviving victims of the fratricidal war that hit the country between 1980-1992 and their families. The central thesis of the essay focuses on the figure of Monseñor Romero and his religious praxis, that of a preferential option for the poor who, once consummated his martyrdom, is still present in the collective unconscious of the country through his example. It is a voice that accompanied his people as a light that illuminates their path

Condiciones institucionales y producción académica de docentes de la Facultad Multidisciplinaria de Occidente de la Universidad de El Salvador

El objetivo de esta investigación fue analizar las condiciones institucionales y la producción académica de los docentes de la Facultad Multidisciplinaria de Occidente de la Universidad de El Salvador. La metodología de la investigación fue cualitativa, de tipo descriptiva y transversal; la muestra fue teórica dirigida a sujetos tipos siendo éstos, autoridades, funcionarios, docentes y estudiantes organizados, a quienes se les entrevistó a través de una guía de preguntas semi-estructuradas. Los resultados principales muestra que en la Universidad de El Salvador existen condiciones institucionales para generación de conocimiento a través de la investigación y la publicación, sin embargo, la burocracia y la carencia de un modelo de universidad dirigido hacia este rumbo deriva para que el académico no asuma su rol y privilegie la actividad netamente docente. La conclusión, es que la Universidad de El Salvador debe generar una política que conduzca la actividad institucional hacia la conformación de un ethos académico y un campo científico capaz de hacer del “Alma Máter” un centro de pensamiento que aporte a la construcción de una sociedad del conocimiento y la equidad. Institutional conditions and academic production of teachers of the Multidisciplinary Faculty of the West of the University of El Salvador The objective of this research was to analyze the institutional conditions and the academic production of the faculty of the Multidisciplinary Faculty of the West of the University of El Salvador. The methodology of the research was qualitative, descriptive and transversal; the sample was aimed at subject types, being these, authorities, officials, teachers and organized students, who were interviewed through a semi-structured questions guide. The main results show that in the University of El Salvador there are institutional conditions for the generation of knowledge through research and publication, however, the bureaucracy and the lack of a university model directed towards this direction derive so that the academic does not assume its role and privilege the teaching activity clearly. The conclusion is that the University of El Salvador must generate a policy that leads the institutional activity toward the formation of an academic ethos and a scientific field capable of making the "Alma Mater" a center of thought that contributes to the construction of a society of knowledge and equity

Concordancia entre la interpretación del clínico y el reporte radiológico definitivo de la radiografía de tórax del paciente mayor de 15 años que consulta a un servicio de urgencias con diagnóstico inicial de neumonía o insuficiencia cardiaca congestiva

Objetivo: Conocer la concordancia entre la interpretación del clínico y la del radiólogo de la radiografía de tórax en pacientes que consultan a un servicio de urgencias de tercer nivel en Bogotá con diagnóstico inicial de neumonía o insuficiencia cardiaca congestiva. Diseño: Estudio de concordancia con variable categórica. Lugar: Fundación Clínica Shaio Población: Radiografías de tórax realizadas a pacientes que consultan al servicio de urgencias con diagnóstico inicial de neumonía o insuficiencia cardiaca congestiva. Intervención: No hay. Mediciones: Índice Kappa, estadística descriptiva, características operativas. Resultados: El porcentaje de acuerdo de la interpretación de la radiografía de tórax entre el clínico y el radiólogo fue de 63,71%, con un porcentaje esperado por el azar de 33,99% y un Kappa de Cohen de 0,45 (IC 95% 0,43 0,52, pmenor que 0,0001). Por subgrupos según tipo de clínico varió entre un Kappa de 0,62 (IC 95% 0,60 0,66) para los internistas y un Kappa de 0,22 (IC 95% 0,21 0,28) para los cardiólogos. Conclusiones: La concordancia en la interpretación de la radiografía de tórax entre el clínico y el radiólogo es moderada. Al evaluarlo por subgrupos según el tipo de clínico que interpreta la radiografía de tórax encontramos una concordancia entre baja y moderada siendo la mejor la de los internistas y la más baja la de los cardiólogos. La concordancia en los demás subgrupos estudiados siempre fue moderada.Objective: To determine the inter-rater agreement between the clinical physician and radiologist interpretation of chest radiography in patients attending an emergency department third level in Bogota initially diagnosed with pneumonia or congestive heart failure. Design: Study of inter-rater agreement with the categorical variable Location: Fundación Clínica Shaio Population: Chest radiographs performed on patients presenting to the emergency department initially diagnosed with pneumonia or congestive heart failure. Intervention: None.Measurements: Cohen's Kappa coefficient, descriptive statistics, operative characteristics. Results: The percentage of agreement on the interpretation of the chest radiograph between the clinician and the radiologist was 63.71 %, with a percentage expected by chance of 33.99 %, and a Cohen´s kappa of 0.45 (95% CI 0.42-0,51 , p menor que 0.0001 ). For subgroups by type of clinical Kappa ranged between 0.61 (95% CI 0.59-0.66) for internists and a Kappa 0.22 (95% CI 0.21-0.28) for cardiologists Conclusions: The agreement between the interpretation of chest radiographs and clinical radiologist was moderate. When tested by subgroups depending on clinical interpreting chest X-1ray found a correlation between low and moderate with the best for internists and the lowestfor cardiologists. The agreement in the other subgroups studied was always moderate.Magíster en Epidemiología ClínicaMaestrí

Rail freight transport and demand requirements : an analysis of attribute cut-offs through a stated preference experiment

This paper analyses the choice between road and rail in Spain where rail market share for freight is still residual. Discrete choice models are estimated with data obtained through a two-phase fieldwork, thus allowing us to carry out a stated preference efficient design for each interviewee. We analyse the existence of attribute cut-offs and the presence of a segment of the population with a zero value of frequency. Our results show that ignoring the existence of cut-offs and segments of the population with polarised valuations can lead to erroneous conclusions in terms of the possibilities of rail for absorbing significant quota

Electric vehicle powertrains with modular battery banks tied to multilevel NPC inverters

Nowadays, the internal combustion engine in vehicles is being replaced by electric motors, giving way to the electric vehicle, which results in reduced environmental impact, higher efficiency and lower emission of greenhouse gases. The powertrain of an electric vehicle is its most prominent subsystem, with the batteries and traction inverter being key components. Thus, due to their relevance, advances in the design of both components are of paramount importance. In this paper, the potential benefits achieved through a powertrain design approach based on combining a modular battery bank with multilevel NPC traction inverter topologies were analyzed, in comparison to a conventional two-level powertrain design. Several aspects were analyzed: modularity, complexity, battery-pack state-of-charge balancing, inverter loss, motor ac voltage harmonic distortion, motor common-mode voltage and reliability. Particularly, from the comparison study developed under the selected design scenario, the proposed design approach, based on modular battery packs and multilevel technology, shows a potential reduction of up to 55% in inverter losses, up to 65% in motor ac-voltage total harmonic distortion, and up to 75% in rms common-mode voltage.Peer ReviewedPostprint (published version

Pulsewidth modulations for the comprehensive capacitor voltage balance of n-level three-leg diode-clamped converters

In the previous literature, the introduction of the virtual-space-vector (VV) concept for the three-level, three-leg neutral-point-clamped converter has led to the definition of pulsewidth modulation (PWM) strategies, guaranteeing a dc-link capacitor voltage balance in every switching cycle under any type of load, with the only requirement being that the addition of the three phase currents equals zero. This paper presents the definition of the VVs for the general case of an n-level converter, suggests guidelines for designing VV PWM strategies, and provides the expressions of the leg duty-ratio waveforms corresponding to this family of PWMs for an easy implementation.Modulations defined upon these vectors enable the use of diode-clamped topologies with passive front-ends. The performance of these converters operated with the proposed PWMs is compared to the performance of alternative designs through analysis, simulation, and experiments.Postprint (published version