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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Design and construction of a bidirectional DCDC converter for an EV application

Hedlund, Magnus January 2010 (has links)
A Sliding Mode Control System for a Bidirectional DCDC Converter was designed and a low voltage prototype was constructed. The control system based its decisions solely on the latest available measurements, which improves performance when changing operative quadrant, since no memory needs reinitializing (such as for PI and state prediction methods). A boost control philosophy was presented, based on a current source approximation. The control was found to be stable without steady-state errors when the variance of the input/output dynamics was high. The target application for the DCDC Converter is an EV (Electric Vehicle) with a flywheel driveline, which puts additional requirements of the converter. Among these are current and voltage control, bidirectionality, and a broad input voltage range. Simulations were performed in Simulink prior to physical implementation, proving functionality of the proposed control system. The physical implementation of the control was done on a digital signal processor with code compiled from C. A median filter was designed to increase measurement efficiency for the current sensors which had shot-like noise distortions.
22

Entre o partir e o chegar : os trabalhadores rurais migrantes em Matão/SP / Between the departure and the arrive : the rural migrant workers in Matão/SP

Pereira, Giovana Gonçalves, 1991- 05 December 2015 (has links)
Orientador: Rosana Aparecida Baeninger / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Filosofia e Ciências Humanas / Made available in DSpace on 2018-08-27T13:57:19Z (GMT). No. of bitstreams: 1 Pereira_GiovanaGoncalves_M.pdf: 3645717 bytes, checksum: ec5de4991b14293da48b4ce7aa220d96 (MD5) Previous issue date: 2015 / Resumo: Esse trabalho teve como objetivo central a análise da migração "permanentemente" temporária de trabalhadores rurais migrantes da cidade de Jaicós/PI para o município de Matão/SP. O emprego de uma metodologia qualitativa, pautada na observação direta, se fez necessário em razão da fluidez entre os espaços de origem e de destino. Nesse sentido, aferimos que as idas e vindas para a colheita da laranja em Matão/SP, se apresentaram como partes estruturantes da dinâmica social de Jaicós/PI e do próprio município de Matão/SP / Abstract: This research was mainly focused on understanding "permanent" temporary migration of rural workers from the city of Jaicós/PI to the city of Matão/SP. The use of qualitative methodology, based on direct observation, was necessary because of the flow between the spaces of origin and destination. As a resulto of research, we verified that the comings and goings for the harvest of orange in Matão/SP are na important sctrucutral parto f the social dynamics of Jaicós/PI / Mestrado / Demografia / Mestra em Demografia
23

Power Control Systems in a Flywheel based All-Electric Driveline

Gonçalves de Oliveira, Janaína January 2011 (has links)
Flywheel systems are attractive in hybrid and electric vehicles due to their ability to handle power during acceleration and braking. The combination of a flywheel device with a battery source has several advantages such as high peak power capacity, high energy density and reduction in the number of charge/discharge cycles of the battery. A flywheel based all-electric driveline is investigated in this thesis. The novelty of the system consists in the use of a double wound flywheel machine, which divides the system in two different power levels. Due to this configuration, the system becomes efficient and can handle the power developed during fast dynamical processes. The complete driveline consists of three main components: the battery, the flywheel machine and the wheel motor. The High-Power (HP) side of the driveline connects the flywheel machine to the wheel motor, whereas the Low-Power (LP) side connects the flywheel machine to the battery. The connections of different components of the system are made electrically through power converter devices. The present thesis focuses on the electrical converters and control strategies used in the flywheel based all-electric driveline. The control of power converters is responsible for the logic and functionality of the driveline, being a challenging step within this project. Different power converter topologies have been investigated: a DC/DC plus a DC/AC converter on the LP side, and an AC/DC/AC converter on the HP side. The design and assembly of the power electronics and their control scheme have been successfully implemented. Different control strategies have been suggested and a complete scaled driveline has been assembled and tested based on previous simulation results. Results have confirmed the functionality of the driveline, where smoothed output power has been obtained from the battery, whereas the flywheel handles power transients on the traction side. An average efficiency of about 87% (battery to wheels) has been obtained. The power converter systems have been shown to be efficient and robust, with control strategies able to handle the peak energy flow in the system. A regenerative braking strategy has been simulated and a wheel-to-wheel efficiency of about 80% has been estimated.
24

Design And Optimization Of A Wave Energy Harvester Utilizing A Flywheel Energy Storage System

Helkin, Steven Alexander 01 January 2011 (has links)
This thesis details the design and optimization of a buoy used to collect renewable energy from ocean waves. The proposed buoy is a point absorber—a device that transforms the kinetic energy of the vertical motion of surface waves into electrical energy. The focus of the research is on the mechanical system used to collect the energy, and methods to improve it for eventual use in an actual wave energy harvester. A flywheel energy storage system was utilized in order to provide an improved power output from the system, even with the intermittent input of force exerted by ocean waves. A series of laboratory prototypes were developed to analyze parameters that are important to the success of the point absorb mechanical system. By introducing a velocity-based load control scheme in conjunction with flywheel energy storage, it was seen that the average power output by the prototype was increased. The generator load is controlled via a relay switch that removes electrical resistance from the generator—this sacrifices time during which power is drawn from the system, but also allows the buoy to move with less resistance. A simulation model was developed in order to analyze the theoretical wave absorber system and optimize the velocity threshold parameters used in the load control. Results indicate that the power output by the system can be substantially improved through the use of a flywheel energy storage control scheme that engages and disengages the electrical load based on the rotational velocity of the flywheel system. The results of the optimization are given for varying-sized generator systems input into the simulation in order to observe the associated trends.
25

Control Designs for Low-Loss Active Magnetic Bearing: Theory and Implementation

Wilson, Brian Christopher David 12 April 2004 (has links)
Control Designs for Low-Loss Active Magnetic Bearings: Theory and Implementation Brian C. D. Wilson 327 Pages Directed by Dr. Panagiotis Tsiotras and Dr. Bonnie Heck-Ferri Active Magnetic Bearings (AMB) have been proposed for use in Electromechanical Flywheel Batteries. In these devices, kinetic energy is stored in a magnetically levitated flywheel which spins in a vacuum. The AMB eliminates all mechanical losses, however, electrical loss, hich is proportional to the square of the magnetic flux, is still significant. For fficient operation, the flux bias, which is typically introduced into the electromagnets to improve the AMB stiffness, must be reduced, preferably to zero. This zero-bias (ZB) mode of operation cripples the classical control techniques which are customarily used and nonlinear control is required. As a compromise between AMB stiffness and efficiency, a new flux bias scheme is proposed called the generalized complementary flux condition(gcfc). A flux-bias dependent trade-off exists between AMB stiffness, power consumption, and power loss. This work theoretically develops and experimentally verifies new low-loss AMB control designs which employ the gcfc condition. Particular attention is paid to the removal of the singularity present in the standard nonlinear control techniques when operating in ZB. Experimental verification is conduced on a 6-DOF AMB reaction wheel. Practical aspects of the gcfc implementation such as flux measurement and flux-bias implementation with voltage mode amplifiers using IR compensation are investigated. Comparisons are made between the gcfc bias technique and the standard constant-flux-sum (cfs) bias method. Under typical operating circumstances, theoretical analysis and experimental data show that the new gcfc bias scheme is more efficient in producing the control flux required for rotor stabilization than the ordinary cfs bias strategy.
26

A organização e análise ergonômica do trabalho do "bóia-fria" = a saga do trabalhador rural da lavoura da cana de açúcar no estado de Pernambuco - do escravo ao bóia-fria, uma história de "sangue, suor e lágrima" / Organization and ergonomic analysis of part time sugar cane workers : the saga of sugar cane workers from Pernambuco - from slave to part time worker, a story of blood, sweat and tear

Risk, Eloah Nazaré Varjal de Melo 16 August 2018 (has links)
Orientadores: Mauro José Andrade Tereso, Roberto Funes Abrahão / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agrícola / Made available in DSpace on 2018-08-16T15:48:37Z (GMT). No. of bitstreams: 1 Risk_EloahNazareVarjaldeMelo_D.pdf: 1920662 bytes, checksum: 2001d109117075fa3e6b4c40c4e34adb (MD5) Previous issue date: 2010 / Resumo: Este trabalho teve por objetivo analisar como se deu a passagem da situação do Bóia-Fria na condição de trabalhador-morador para trabalhador-credor, a partir das mudanças operadas nas condições de trabalho, quando da institucionalização da CLT - Consolidação das Leis Trabalhistas - como Regime de Trabalho e suas consequências. A análise histórica foi desenvolvida com foco nos Engenhos de cana-de-açúcar do Estado de Pernambuco. A pesquisa, numa abordagem sócio-antropológica permitiu conhecer a gênese do Bóia-Fria, desde o período do Brasil Colônia até os dias atuais, onde se desenvolveram suas relações sociais e de trabalho, suas lutas pela sobrevivência e reconhecimento social. Permitiu ainda, conhecer com base nos fundamentos da Ergonomia, o trabalho desenvolvido pelo Bóia-Fria nas perspectivas física, psicológica e cognitiva, cujos resultados apontam para uma categoria de trabalhador rural em vias de extinção em decorrência do avanço da mecanização no corte da cana. O alto índice de analfabetismo se apresenta como um vetor natural para o aproveitamento dessa categoria em outras atividades que não sejam àquelas relacionadas ao cultivo e corte da cana-de-açúcar, o que sinaliza grande dificuldade de inserção social e mudança qualitativa de vida / Abstract: The present work had as the main goal to analyse the shifting condition of the part time workers ("bóia-fria") due to the creation of the labour law (CLT - Consolidação das Leis Trabalhistas) and the consequences, when he abandons the farm as his place of living. The historical analysis was developed aiming the sugar cane production and processing system in the state of Pernambuco. Through a social anthropological approach, this research tried to understand the origin of the part time workers ("bóia-fria") since when Brazil was a colony to nowadays, how the working conditions and social relations had developed and changed, and their survival struggle and social acknowledgement. This work also investigated, based on the Ergonomics basics, the work developed by the part time workers ("bóia-fria"), in physical, psychological and cognitive viewpoints. The results point to a rural worker category close to extinction due to the advancement of the mechanization of the sugar cane harvesting. The high index of illiteracy presents itself as a natural vector to the reapplication of this category in other activities not related to sugar cane harvesting, pointing a great difficult of social insertion and qualitative chance of life / Doutorado / Doutor em Engenharia Agrícola
27

Optimal control and stability of four-wheeled vehicles

Masouleh, Mehdi Imani January 2017 (has links)
Two vehicular optimal control problems are visited. The first relates to the minimum lap time problem, which is of interest in racing and the second the minimum fuel problem, which is of great importance in commercial road vehicles. Historically, minimum lap time problems were considered impractical due to their slow solution times compared with the quasi-steady static (QSS) simulations. However, with increasing computational power and advancement of numerical algorithms, such problems have become an invaluable tool for the racing teams. To keep the solution times reasonable, much attention still has to be paid to the problem formulation. The suspension of a Formula One car is modelled using classical mechanics and a meta-model is proposed to enable its incorporation in the optimal control problem. The interactions between the aerodynamics and the suspension are thereby studied and various related parameters are optimised. Aerodynamics plays a crucial role in the performance of Formula One cars. The influence of a locally applied perturbation to the aerodynamic balance is investigated to determine if a compromise made in design can actually lead to lap time improvements. Various issues related to minimum lap time calculations are then discussed. With the danger of climate change and the pressing need to reduce emissions, improvements in fuel consumption are presently needed more than ever. A methodology is developed for fuel performance optimisation of a hybrid vehicle equipped with an undersized engine, battery and a flywheel. Rather than using the widely used driving cycles, a three-dimensional route is chosen and the optimal driving and power management strategy is found with respect to a time of arrival constraint. The benefits of a multi-storage configuration are thereby demonstrated. Finally, the nonlinear stability of a vehicle model described by rational vector fields is investigated using region of attraction (RoA) analysis. With the aid of sum-of-squares programming techniques, Lyapunov functions are found whose level sets act as an under-approximation to the RoA. The influence of different vehicle parameters and driving conditions on the RoA is studied.
28

Mathematical simulation and optimization of a stand alone zero emissions hybrid system based on renewable energy sources / Μαθηματική προσομοίωση και βελτιστοποίηση μιας υβριδικής αυτόνομης μηδενικών ρύπων μονάδας παραγωγής ηλεκτρικής ενέργειας που τροφοδοτείται αποκλειστικά από ΑΠΕ

Προδρομίδης, Γεώργιος 01 August 2014 (has links)
Renewable Energy Sources (RES) are the most promising resources of energy production for everyday life. Therefore, the precise combination of RES based technologies into hybrid systems could provide the solution to several energy problems facing the planet. The motivation of the present research study is the total understanding of the prevailing phenomena by using RES equipment in several projects. This thesis will focus on standalone hybrid RES based systems. By presenting the RES systems the necessity of buffering systems will become apparent as the most crucial parts of off-grid systems. Therefore, the most well-established buffering technologies will be analytically presented in order to be subsequently embodied into the simulated RES applications. Following the above theoretical approach of RES based equipment and hybrid systems in general, this thesis will focus on a more applied research study comprising the energetic and economical simulation and optimization of a RES based stand alone system that is already installed in Leicestershire, UK. Based on local meteorological data, an optimization strategy has been developed to identify the most economical and efficient scenarios for electricity generation to cover the desirable load on an annual basis. Furthermore, the environmentally-friendly character of the system was highly concerned with emissions reduction; therefore the capability of an off-grid system was also investigated. The feasibility of RES based systems for electricity supply will then be presented for four different Greek Islands. Three specific typical loads have been selected to be covered and the grid connection was considered optional. Up to this point the simulation and optimization procedures were applied by using the HOMER software tool in order to investigate the most suitable well-established platform in the world. After the theoretical research study on the most well-known platform of HOMER an innovative optimization theory based on the energy part of a hybrid system will be presented in order to select the most efficient system according to the desired requirements and the location of a RES based project. This thesis will then focus on the design and operation of an autonomous hybrid system under real-life meteorological conditions which is capable of simulating several loads assumed to cover the electricity demands of small buildings. The specific hybrid system embodies technologies that use photovoltaic and wind energy in combination with an electrochemical storage bank. Experiments on the coverage of annual loads regarding a typical house, a typical country house and a small company were also performed to prove the feasibility of the stand-alone system. The same established RES project was then simulated on a yearly basis using the HOMER software platform to determine real-time results. The above analysis revealed that HOMER software cannot successfully simulate the operation of such a system, therefore the design of a new mathematical model to produce results similar to those of the experimental process was considered essential based on a new optimization strategy. / Οι Ανανεώσιμες Πηγές Ενέργειας (ΑΠΕ) αποτελούν τις πιο πολλά υποσχόμενες πηγές στον τομέα της παραγωγής της ηλεκτρικής ενέργειας μέσα στην ανθρώπινη καθημερινότητα. Έτσι ο ακριβής συνδυασμός των ΑΠΕ σε υβριδικά συστήματα θα μπορούσε να αποτελέσει τη λύση στο μεγάλο ενεργειακό πρόβλημα που αντιμετωπίζει ο πλανήτης τα τελευταία χρόνια και όσο περνάει ο καιρός αυτό φαίνεται να διογκώνεται. Το κίνητρο για την εκπόνηση της παρούσας διδακτορικής διατριβής στηρίζεται στην ανάγκη για απόλυτη κατανόηση των φαινομένων που λαμβάνουν χώρα κατά τη χρήση των ΑΠΕ σε διάφορα συστήματα για την παραγωγή ηλεκτρικής ενέργειας. Επιπλέον, μέσα από αυτή την έρευνα θα φανεί πως οι καιρικές συνθήκες επηρεάζουν τη συμπεριφορά ενός υβριδικού συστήματος και σε ποιό ποσοστό. Ακόμα περιμένουμε να γίνει φανερό το πόσο σημαντική είναι η σωστή επιλογή των τεχνολογιών σύμφωνα με τις ηλεκτρικές ανάγκες που πρέπει να καλυφθούν από ένα εγκατεστημένο σύστημα. Στη συνέχεια της παρούσας εργασίας μελετήθηκε κάτω από ποιες συνθήκες ένα αυτόνομο υβριδικό σύστημα μπορεί να είναι εφικτό καθώς και πόσο ακριβή αποτελέσματα μπορούν αν δώσουν τα θεωρητικά μαθηματικά μοντέλα επάνω στην πρόβλεψη της λειτουργίας ενός συστήματος. Τέλος, παρουσιάστηκε πως μπορεί να ενισχυθεί ο οικολογικός χαρακτήρας ενός συστήματος ενώ την ίδια στιγμή αποκαλύφθηκε η κύρια αδυναμία του κατά τη λειτουργία καθώς και πως αυτή μπορεί να λυθεί με τη χρήση καινοτόμων συσκευών για την αποθήκευση ενέργειας. Μέσω της παρούσας διδακτορικής διατριβής αποδείχθηκε πως ένα υβριδικό σύστημα υποστηριζόμενο από ΑΠΕ μπορεί να μετατραπεί σε εντελώς αυτόνομο με ενισχυμένο τον οικολογικό του χαρακτήρα και με την οικονομική και ενεργειακή βιωσιμότητά του να κυμαίνεται σε υψηλά επίπεδα. Το παραπάνω συμπέρασμα προέκυψε μέσω θεωρητικών αλλά και πειραματικών προσομοιώσεων διάφορων υβριδικών μονάδων. Αυτό αποτελεί ίσως το πιο ενθαρρυντικό στοιχείο για πλήρη αξιοποίηση των ΑΠΕ προκειμένου να καλυφθούν οι παγκόσμιες ενεργειακές ανάγκες με τρόπους εντελώς φιλικούς προς το περιβάλλον στο άμεσο μέλλον.

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