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Macchine ed Azionamenti
Elettrici
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Development of DC/AC power converters for applications requiring high efficiency
Rizzoli Gabriele - Ciclo XXVIII - 2016
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Abstract - Silicon-based power devices have dominated power electronics applications over the last decades. Research and development in microelectronics have pushed the performance of power devices to face some fundamental limitations of silicon material. Wide bandgap semiconductors, such as silicon carbide, offer a solution to the pressing energy efficiency performance requirements of power electronic systems. Silicon carbide power devices can operate at higher temperatures, higher frequencies, and generate less power losses as compared to traditional silicon-based technologies. The use of wide bandgap transistors, however, is not the only way to increase the efficiency of the converters. Special DC to AC topologies, named soft switching converters, can be adopted as well in order to reduce the switching losses of transistors. The development of DC to AC power converters for applications requiring high efficiency is presented in this thesis. Silicon and silicon carbide based inverters, as well as soft switching inverters, have been analyzed and fabricated for performance comparison.
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Power converters and electric drives for smart grid applications
Bonavoglia Marco - Ciclo XXVII - 2015
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Abstract - The present dissertation aims to explore, theoretically and experimentally, the problems and the potential advantages of different types of power converters for "Smart Grid" applications, with particular emphasis on multi-level architectures, which are attracting a rising interest even for industrial requests.
The models of the main multilevel architectures (Diode-Clamped and Cascaded) are shown. The best suited modulation strategies to function as a network interface are identified. In particular, the close correlation between PWM (Pulse Width Modulation) approach and SVM (Space Vector Modulation) approach is highlighted.
An innovative multilevel topology called MMC (Modular Multilevel Converter) is investigated, and the single-phase, three-phase and "back to back" configurations are analyzed. Specific control techniques that can manage, in an appropriate way, the charge level of the numerous capacitors and handle the power flow in a flexible way are defined and experimentally validated.
Another converter that is attracting interest in "Power Conditioning Systems" field is the "Matrix Converter". Even in this architecture, the output voltage is multilevel. It offers an high quality input current, a bidirectional power flow and has the possibility to control the input power factor (i.e. possibility to participate to active and reactive power regulations). The implemented control system, that allows fast data acquisition for diagnostic purposes, is described and experimentally verified.
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Analysis and design of high performance multiphase electric drives for vehicle and aircraft application
Rini
Giancarlo - Ciclo XXVII - 2015
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Abstract -
The first part of this thesis has focused on the construction of a twelve-phase asynchronous machine for More Electric Aircraft (MEA) applications. In fact, the aerospace world has found in electrification the way to improve the efficiency, reliability and maintainability of an aircraft. This idea leads to the aircraft a new management and distribution of electrical services. In this way is possible to remove or to reduce the hydraulic, mechanical and pneumatic systems inside the aircraft. The second part of this dissertation is dedicated on the enhancement of the control range of matrix converters (MCs) operating with non-unity input power factor and, at the same time, on the reduction of the switching power losses. The analysis leads to the determination in closed form of a modulation strategy that features a control range, in terms of output voltage and input power factor, that is greater than that of the traditional strategies under the same operating conditions, and a reduction in the switching power losses.
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Grid Connected Doubly Fed Induction Generator Based Wind Turbine under LVRT
Chandrasekaran
Subramanian - Ciclo XXVI - 2014
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Abstract - This project concentrates on the Low Voltage Ride Through (LVRT) capability of Doubly Fed Induction Generator (DFIG) wind turbine. The main attention in the project is, therefore, drawn to the control of the DFIG wind turbine and of its power converter and to the ability to protect itself without disconnection during grid faults. It provides also an overview on the interaction between variable speed DFIG wind turbines and the power system subjected to disturbances, such as short circuit faults. The dynamic model of DFIG wind turbine includes models for both mechanical components as well as for all electrical components, controllers and for the protection device of DFIG necessary during grid faults. The viewpoint of this project is to carry out different simulations to provide insight and understanding of the grid fault impact on both DFIG wind turbines and on the power system itself. The dynamic behavior of DFIG wind turbines during grid faults is simulated and assessed by using a transmission power system generic model developed and delivered by Transmission System Operator in the power system simulation toolbox Digsilent, Matlab/Simulink and PLECS.
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Diagnosis and Fault Detection in Electrical Machines and Drives based on Advanced Signal Processing Techniques
Yasser
Gritli- Ciclo XXVI - 2014
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Abstract - Electrical machines are critical components in several industries, that safety, and reliability are mandatory. In this context, the issues of electrical machine fault detection and diagnosis is growing rapidly. Although electrical machines are very reliable, they are subjected to many electrical and mechanical failures modes, and the challenge is to detect them at an early stage in order to provide, whenever possible operational continuation. Recently inverter fed machines for variable speed drives are spreading in many industrial fields and the diagnosis of mechanical and electrical faults becomes a more complex issue. In fact the variables usually monitored for diagnostic purposes are inevitably influenced by the control system. In this sense the techniques developed for line-fed induction motors and open loop drives cannot be used straightforward as the control system of the drive changes the effects that the fault would introduces in several quantities, hence not allowing a proper detection and quantification of the fault itself. A further complication, in the field of electrical machine diagnosis, which is still one of the major concerns under investigation, is the possibility to develop diagnostic techniques that could retrieve a robust fault index in continuous non-stationary operating conditions. In the present thesis, a new methodology of diagnosis based on advanced use of time-frequency technique analysis is presented. More precisely, a new fault index that allows tracking fault components is defined. More in detail, a frequency sliding is applied to the signals being analyzed, so that each single fault frequency component is shifted into a pre?xed single frequency band. Then, the DWT is applied to the resulting signal to extract the fault signature in the chosen frequency band. Once the state of the machine has been qualitatively diagnosed, a quantitative evaluation of the fault degree is achieved by energy evaluation of the issued wavelet signals.
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Non-Linear Analysis and Design of Synchronous Bearingless Multiphase Permanent Magnet Machines and Drives
Stefano
Serri - Ciclo XXV - 2013
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Abstract - A complete design process for bearingless multiphase machines and drives is developed in this thesis. A numerical algorithm for non-linear magnetic analysis of multiphase surface-mounted PM machines with semi-closed slots is first presented, based on the equivalent magnetic circuit method. By using a modular structure geometry it allows to design whatever typology of windings distribution, calculating output torque and radial forces acting on the moving part of the machine.
In order to design the suspension control system, an analytical model for radial forces calculation in multiphase bearingless Surface-Mounted Permanent Magnet Synchronous Motors (SPMSM) is presented, allowing to predict amplitude and direction of the force, depending on the values of torque current, of levitation current and of rotor position. Based on the space vectors method, the analysis of the machine also during transients is carried out, taking all the possible interactions between stator and rotor mmf harmonic components into account. This method, representing the electromagnetic model of the machine, was integrated with a three-dimensional mechanical model of a motor with one shaft-end constrained by a mechanical bearing and the other one only supported by the radial forces developed in the interactions between magnetic fields, realizing a three-degrees of freedom bearingless system.
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Controllo Vettoriale Generalizzato Per Macchine Elettriche Trifase
Alessio
Pilati - Ciclo XXIV - 2012
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Abstract - Nell’ambito della presente tesi e' descritto un approccio generalizzato per il controllo delle macchine elettriche trifasi; la prima parte è incentrata nello sviluppo di una metodologia di modellizzazione generale, ossia in grado di descrivere, da un punto di vista matematico, il comportamento di una generica macchina elettrica, che possa quindi includere in sé stessa tutte le caratteristiche salienti che possano caratterizzare ogni specifica tipologia di macchina elettrica. Il passo successivo è quello di realizzare un algoritmo di controllo per macchine elettriche che si poggi sulla teoria generalizzata e che utilizzi per il proprio funzionamento quelle grandezze offerte dal modello unico delle macchine elettriche. La tipologia di controllo che è stata utilizzata è quella che comunemente viene definita come controllo ad orientamento di campo (FOC), per la quale sono stati individuati degli accorgimenti atti a migliorarne le prestazioni dinamiche e di controllo della coppia erogata. Per concludere verrà presentata una serie di prove sperimentali con lo scopo di mettere in risalto alcuni aspetti cruciali nel controllo delle macchine elettriche mediante un algoritmo ad orientamento di campo e soprattutto di verificare l’attendibilità dell’approccio generalizzato alle macchine elettriche trifasi. I risultati sperimentali confermano quindi l’applicabilità del metodo a diverse tipologie di macchine (asincrone e sincrone) e sono stati verificate nelle condizioni operative più critiche: bassa velocità, alta velocità bassi carichi, dinamica lenta e dinamica veloce.
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Hybrid e-CVT Power Split Drivelines
Piero
Corbelli - Ciclo XXIII - 2011
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Abstract - This thesis deals with the application of an electrical hybrid power line technology
which has previously been widely applied in the automotive field: the series-parallel power
split e-CVT (electrical continuously variable transmission) device.
Hybrid drivelines have been used since the birth of the automobile, where battery
supplied electrical motors were used to enhance the performances of the early internal
combustion engines, which had very low powers. After the World War I the technical
progress brought to powerful ICE (internal combustion engine) technologies, and the
electrical assisted hybrid solutions were totally abandoned. Only in the last 35 years a new
interest for hybrid electric vehicles has been discovered, thanks to the technological advances
of electric machines driven by static power electronic converters, and to new and more
performing energy storage devices (Lithium batteries, supercapacitors, fuel cells, etc.). The continuously variable transmission is a technological solution applied on many
vehicles, realized in various ways, by means of mechanical, hydro-static,
hydro-dynamic, electric conversion systems. Its main feature is to change continuously the speed ratio
between two shafts, avoiding the presence of shifting gears, clutches and torque converters,
often very critical and inefficient drivelines components. In this Ph.D. work the e-CVT device
has been conveniently applied on three particular fields: Terrestrial off-road vehicles; Marine ship propulsion;Wind energy conversion systems..
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Modulation Techniques for Multi-Phase Converters and Control Strategies for Multi-Phase Electric Drives
Michele
Mengoni - Ciclo XXII - 2010
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Abstract - The first area of research is related to the control of three phase induction motors with high dynamic performance and the sensorless control in the high speed range. The management of the operation of induction machine without position or speed sensors awakes interest in the industrial world due to the increased reliability and robustness of this solution combined with a lower cost of production and purchase of this technology compared to the others available in the market. The second part of this dissertation is dedicated to the multi-phase systems. This technology, in fact, is characterized by a number of issues worthy of investigation that make it competitive with other technologies already on the
market.
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Induction Motor Diagnosis in Variable Speed Drives
Andrea
Stefani - Ciclo XXII - 2010
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Abstract - Il presente lavoro di tesi ha come oggetto la diagnostica per il rilevamento di guasti di tipo elettrico in macchine asincrone per azionamenti a velocità variabile. La presenza di un sistema di controllo in catena chiusa influenza inevitabilmente le variabili normalmente analizzate per fini diagnostici, rendendo talvolta inefficaci le tecniche impiegate per macchine alimentate direttamente da rete. Si rende pertanto necessario lo sviluppo di metodologie diagnostiche specifiche per il tipo di azionamento e di applicazione e che preveda anche il monitoraggio di variabili interne al controllo stesso. Un ulteriore complicazione per il rilevamento di guasti in azionamenti a velocità variabile deriva dalla difficoltà di ottenere un indice diagnostico che sia sufficientemente robusto ed affidabile in condizioni non stazionarie. Qui di seguito tre diverse tecniche diagnostiche sono proposte al fine di rilevare guasti di rotore (barre rotte) in sistemi per la trazione ferroviaria e asimmetrie di statore e di rotore in macchine asincrone a doppia alimentazione largamente impiegate in sistemi di generazione
eolica.
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Design optimization and control strategies for PM Multiphase Tubular Linear Actuators
Filippo
Milanesi - Ciclo XXI - 2009
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Abstract - The demand for linear electric machine, specially for controlled motion, has registered
a continuous growth in recent years, since its integration in industrial applications leads to
important advantages. Furthermore, the tubular structure seems to be attractive for
industrial purposes due to both its closed form and the inherently absence of attractive
force between the stator and the mover. In this thesis the fundamental characteristics of the linear machines will be illustrated
in order to highline their main advantages and drawbacks. Particular attention will be paid to
the technologic developments in soft and hard magnetic materials, which enable the
industrial realization of motor with high force density, improved dynamic behaviour within a
relatively low cost. Finally the attention will be focused on permanent magnet (PM) tubular linear
motors.
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Control
of Matrix Converters
Luca Zarri - Ciclo
XIX - 2007
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Abstract - A matrix converter (MC) is an array of controlled semiconductor switches
that directly connect each input phase to each output phase, without any
intermediate dc link. The main advantage of MCs is the absence of bulky reactive
elements, that are subject to ageing, and reduce the system reliability.
Furthermore, MCs provide bidirectional power flow, nearly sinusoidal input and output
waveforms and controllable input power factor. Therefore MCs have received
considerable attention as a good alternative to voltage-source inverter
(VSI) topology. Chapter 1 gives an overview of the basic principles of matrix converters. Chapter 2
summarises the most important modulation strategies for matrix
converter, whereas Chapter 3 proposes two novel modulation techniques that allows
obtaining a better performance in terms of number of commutations and
current distortion. Chapter 4 and 5 concern the stability problem. In those Chapters the
unstable behaviour of matrix converter is explained and some solutions are
proposed. Chapter 6 analyses in details the quality of the input currents.
Finally, Chapter 7 presents and assesses a complete electric drive for induction motor
based on matrix converter.
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Multilevel
Converters: Dual Two-Level Inverter Scheme
Alberto Lega - Ciclo
XIX - 2007
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Abstract - The dissertation has the aim to investigate the multilevel converters topology, starting from the
basis. A survey of multilevel topologies and modulation will introduce to the accurate description of
the dual 2-level inverter. Two modelling methodology for this converter will be analysed: one is the
use of space vectors, the other is based on complex duty-cycle theory. Using these mathematical
tools, a power sharing technique will be presented together to the analytical study of its effects
during commutations. To conclude, two converter have been built and some experimental results
will be shown, proving that power sharing can be realized.
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