Design and characterization of a solar concentration thermo-electric generator

Este proyecto aborda el diseño de un generador termoeléctrico de concentración solar para la conversión directa de radiación solar en electricidad. El sistema se ha sometido a una serie de ensayos a diferentes irradiancias y condiciones exteriores para evaluar las mejoras del concentrador. Además, su desempeño se compara con un TEG más grande sin el mencionado mecanismo de concentración. La generación máxima alcanzada es de 1,6mW a 1050W/m2, cuatro veces la producción del prototipo sin concentrador. Finalmente, se realiza un análisis de escalabilidad para evaluar la viabilidad del prototipo para suministrar equipos auxiliares en campos de energía fotovoltaica.This project presents the design and evaluation of a solar concentration thermoelectric generator(TEG) for harvesting energy directly from solar radiation. With the aim of assessing the improved performance obtained by the concentration system, a test campaign at different irradiances and environmental conditions has been carried out. Additionally, results are compared to a larger TEG without the mentioned concentration mechanism. The maximum power generation was 1.6mW at 1050W/m2, 4 times the production of the non-concentrating TEG. Finally, scalability analysis is carried out in order to assess the feasibility of supplying auxiliary equipment in photovoltaic energy harvesting farms.Grado en Ingeniería en Electrónica y Automática Industria

Modeling and Full Decoupling Control of a Grid-Connected Five-Level Diode-Clamped Converter

This paper presents a novel approach to deal with the regulation of the dc-link capacitor voltages and ac-side currents in a grid-connected five-level diode-clamped converter. Due to the controllability problems of this topology, guaranteeing a solid current control and, mainly, a correct dc-link voltage sharing, represents a complex technical challenge. With the purpose of coping with it, an averaged model that describes the system dynamics at both sides of the converter is presented, assuming that a modulation strategy is integrated in the system to generate the switching sequence. In order to derive the proposed model, no restriction concerning the use of only the three nearest vectors to the desired voltage reference is taking into account. Then, several changes of variables are carried out in the model equations to obtain control input decoupling for control purposes, while reducing the complexity of the model as well. Finally, the voltage and current controllers are designed separately using different control inputs in a straightforward way. Neither auxiliary hardware nor complicated mathematical calculations are required to achieve the control objectives. The effectiveness and good performance of the system under the proposed control approach is validated by simulation results, suggesting that the five-level diode-clamped converter can be a solid solution as an interfacing system connected to the utility grid for, e.g., industrial drives or renewable energy applications.Ministerio de Economía y Competitividad y Unión Europea : DPI2016-75294-C2-1-RMinisterio de Economía y Competitividad y Unión Europea : DPI2013-41891-

Asymptotic rejection of sinusoidal disturbances based voltage balance control in back-to-back power converters

This paper addresses the imbalance problem of the dc-link capacitor voltages in the three-level diode-clamped back-to-back power converter. In order to cope with it, a mathematical analysis of the capacitor voltage difference dynamics, based on a continuous model of the converter, is first carried out. It leads to an approximated model which contains explicitly several sinusoidal functions of time. In view of this result, the voltage imbalance phenomenon can be addressed as an output regulation problem, considering the sinusoidal functions as exogenous disturbances. Thus, a novel approach to deal with the mentioned problem in the back- to-back converter is presented. Then, the particular features of the disturbances are used to design several controllers. They all follow an asymptotic disturbance rejection approach. In this way, the estimations of the disturbances are used to apply a control law that cancels them while regulating the capacitor voltage balance as well. Finally, the performance of the proposed control laws is evaluated, presenting the simulation results obtained when the different controllers are implemented.MICINN-FEDER DPI2009-0966

A Java based simulation for basic control

7th IFAC Symposium on Advances in Control Education 21/06/2006 MadridIn this paper we present a java based simulator for control education in basiccourses. The application has been developed using the well known tool Easy JavaSimulation.The objective of the application is to help the student to learn the design of classiccontrollers such as P,PI, PID, etc testing the tuning procedures to control the position ofan antenna controlled by a DC motor. Thus the application allows the student to choosethe parameters of the antenna and the DC motor, to choose the controller to be used andits parameters and finally to simulate the closed loop system observing the evolution ofthe signals as well as a 3-D view. Furthermore, in order to show the real behavior of thesystem, dead zone, saturation, disturbances and non-linearities can be added to the model.This application has been used by the authors to teach a basic control course at EscuelaSuperior de Ingenieros (University of Seville) as virtual laboratory.Moreover, since the application is java based, this can be used by the students from theauthors’ web pages and this can also be installed in the student’s laptop (whichever theplatform is) by downloading it from the authors web page (Limon and Salas, 2003Ministerio de Ciencia y Tecnología DPI2004-07444Ministerio de Ciencia y Tecnología DPI2003-0042

Integrated Control of Five-Level Diode-Clamped Rectifiers

This paper presents an approach for dealing with the control of five-level, diode-clamped rectifiers. The control of such converters is challenging since the voltage balancing among capacitors is not a trivial task. Some of the existing approaches that cope with this problem use specific modifications of one of the traditional modulation techniques such as using redundant vectors in SVM. The main feature of the proposed technique is that part of the modulation is considered in the system equations and, in this way, the voltage balance can be solved designing a specific controller for this problem. As a result, several levels are used within a switching period. Furthermore, it is shown that the proposed approach hardly affects the control of active and reactive powers and total dc-link voltage in such a way that the well-known direct power control (DPC) can be applied. As a consequence, the resultant modulation stage is simpler than other techniques based on, e.g., space vector modulation (SVM). The effectiveness and good performance of the system under the proposed control approach are validated by both simulation and experimental results.Ministerio de Economía y Competitividad y Unión Europea : DPI2016-75294-C2-1-

Voltage Balance for Five-Level DCC Based on Mixed-Integer Linear Programming

In power converters, the modulation stage commands the switching devices to drive the converter outputs to the voltage required by the inner controllers in order to achieve their objectives. However, in multilevel converters, the modulation may be in charge of an ad ditional goal since it also has to tackle with the capacitor voltage balancing issue. This paper formulates the modulation of multilevel three-phase power converters, specifically a five-level diode-clamped converter (DCC), as a mixed-integer linear optimization prob lem. In this paper, it is shown that the presented optimization problem can deal with the capacitor voltage balance at the same time that the number of commutations is minimized. The problem is solved offline and its solution is stored in a lookup table to be used during normal operation. Then, an online procedure to obtain the levels that modulate each phase from the lookup table is given. Comparisons with model predictive control, space-vector based algorithms and other modulation approaches are presented in simulations. Several experimental results are presented showing the feasibility of this approach with changes in the operating conditions

How happy are young economists in their jobs?

This paper investigates issues of job satisfaction and competencies among economists. For this purpose, we use a data set gathered in 2006 at the University of Seville. Ordered logit analysis is used to analyze the determinants of an economist’s overall satisfaction at work. The results demonstrate that competency mismatches matter for reported overall job satisfaction

Los factores determinantes del emparejamiento educación-empleo: Evidencia a partir de una nueva muestra de economistas

Esta comunicación utiliza datos primarios para analizar los determinantes del (des)ajuste educativo de una cohorte de jóvenes economistas formados en la Universidad de Sevilla. Metodológicamente estima un modelo logit multinomial, en el que las categorías son el buen emparejamiento, la sobrecualificación, la infracualificación y el mal emparejamiento. Dejando de lado las características del empleo, nuestros resultados confirman que existe un efecto diferencial por sexo en el desajuste educativo y que además la nota media y el tiempo de búsqueda de empleo afectan a la clasificación de los egresados en las diferentes categorías

Voltage balancing in three-level neutral-point-clamped converters via Luenberger observer

This paper addresses the problems associated with the dc-link capacitor voltages of the three-level neutral-point-clamped power converter: the imbalance of the capacitor voltages as well as the presence of an ac-voltage low-frequency oscillation in the dc link of the converter. In order to cope with them, a mathematical analysis of the capacitor voltage difference dynamics, based on a direct average continuous model, is carried out, considering a singular perturbation approach. The analysis leads to a final expression where a sinusoidal disturbance appears explicitly. Consequently, the two problems can be handled together using the ordinary formulation of a problem of regulating the output of a system subject to sinusoidal disturbances, applying classical control theory to design the controller. In this way, the controller is designed including the disturbance estimate provided by a Luenberger observer to asymptotically cancel the disturbance, while keeping also balanced the capacitor voltages. Experiments for a synchronous three-level neutral-point-clamped converter prototype are carried out to evaluate the performance and usefulness of the converter working as a grid-connected inverter under the proposed control law.MICINN-FEDER DPI2009-09661Junta de Andalucía P07-TIC-0299

El mercado de trabajo de los economistas: análisis de los factores determinantes de la duración del primer desempleo.

Este trabajo examina los determinantes de la duración del primer desempleo de una cohorte de jóvenes graduados: los que obtuvieron su titulación en el curso 2001/2002 en las carreras del área económica de la Universidad de Sevilla. Tras estimar un logit ordenado para datos de duración se obtiene la conclusión de que la nota media del egresado es un favor que coadyuva a la inserción laboral. Además, haber trabajado durante los estudios acelera el proceso de inserción laboral, al igual que haber hecho prácticas durante la carrera. Se tarda más en conseguir el primer empleo cuanto menor es el nivel educativo de la madre. Además, no se observan diferencias estadísticamente significativas en el acceso al primer empleo por género o según el tipo de estudios finalizados en el área económica.duración del desempleo, transición universidad-empleo, microeconometría,modelo logit ordenado, unemployment, duration, university-to-work transition, microeconometrics,ordered logit model.