京都大学 / 新制・課程博士 / 博士(地域研究) / 甲第24026号 / 地博第305号 / 新制||地||118(附属図書館) / 京都大学大学院アジア・アフリカ地域研究研究科グローバル地域研究専攻 / (主査)教授 藤倉 達郎, 教授 D'SOUZA Rohan Ignatious, 教授 中溝 和弥, 准教授 池亀 彩 / 学位規則第4条第1項該当 / Doctor of Area Studies / Kyoto University / DGAM

Over the past ten years, there has been increased use of electronic power processing in alternative, sustainable, and distributed energy sources, as well as energy storage systems, transportation systems, and the power grid. Three-phase voltage source converters (VSCs) have become the converter of choice in many ac medium- and high-power applications due to their many advantages, such as high efficiency and fast response. For transportation applications, high power density is the key design target, since increasing power density can reduce fuel consumption and increase the total system efficiency. While power electronics devices have greatly improved the efficiency, overall performance and power density of power converters, using power electronic devices also introduces EMI issues to the system, which means filters are inevitable in those systems, and they make up a significant portion of the total system size and cost. Thus, designing for high power density for both power converters and passive components, especially filters, becomes the key issue for three-phase converters. This dissertation explores two different approaches to reducing the EMI filter size. One approach focuses on the EMI filters itself, including using advanced EMI filter structures to improve filter performance and modifying the EMI filter design method to avoid overdesign. The second approach focuses on reducing the EMI noise generated from the converter using a three-level and/or interleaving topology and changing the modulation and control methods to reduce the noise source and reduce the weight and size of the filters. This dissertation is divided into five chapters. Chapter 1 describes the motivations and objectives of this research. After an examination of the surveyed results from the literature, the challenges in this research area are addressed. Chapter 2 studies system-level EMI modeling and EMI filter design methods for voltage source converters. Filter-design-oriented EMI modeling methods are proposed to predict the EMI noise analytically. Based on these models, filter design procedures are improved to avoid overdesign using in-circuit attenuation (ICA) of the filters. The noise propagation path impedance is taken into consideration as part of a detailed discussion of the interaction between EMI filters, and the key design constraints of inductor implementation are presented. Based on the modeling, design and implementation methods, the impact of the switching frequency on EMI filter weight design is also examined. A two-level dc-fed motor drive system is used as an example, but the modeling and design methods can also be applied to other power converter systems. Chapter 3 presents the impact of the interleaving technique on reducing the system passive weight. Taking into consideration the system propagation path impedance, small-angle interleaving is studied, and an analytical calculation method is proposed to minimize the inductor value for interleaved systems. The design and integration of interphase inductors are also analyzed, and the analysis and design methods are verified on a 2 kW interleaved two-level (2L) motor drive system. Chapter 4 studies noise reduction techniques in multi-level converters. Nearest three space vector (NTSV) modulation, common-mode reduction (CMR) modulation, and common-mode elimination (CME) modulation are studied and compared in terms of EMI performance, neutral point voltage balancing, and semiconductor losses. In order to reduce the impact of dead time on CME modulation, the two solutions of improving CME modulation and compensating dead time are proposed. To verify the validity of the proposed methods for high-power applications, a 100 kW dc-fed motor drive system with EMI filters for both the AC and DC sides is designed, implemented and tested. This topology gains benefits from both interleaving and multilevel topologies, which can reduce the noise and filter size significantly. The trade-offs of system passive component design are discussed, and a detailed implementation method and real system full-power test results are presented to verify the validity of this study in higher-power converter systems. Finally, Chapter 5 summarizes the contributions of this dissertation and discusses some potential improvements for future work. / Ph. D.

With the increasing demands on electronic loads (e.g. desktop, laptop, monitor, LED lighting and server) in modern technology-driven lives, performance of switched-mode power supply (SMPS) for electronics have been growing to prominence. As front-end converters in typical SMPS structure, ac-dc power-factor correction (PFC) circuits play a key role in regulations of input power factor, harmonics and dc output voltage, which has a decisive effect on entire power-supply performances. Universal ac-line and low-power system (90–264 Vrms, up to 300–400 W) is one of the most common power-supply specifications and boost-derived PFC topologies have been widely used for the purpose. In order to concurrently achieve high efficiency and low-cost system in the PFC stage, zero-current switching (ZCS) control schemes are highly employed in control principles. Representative schemes are discontinuous conduction mode (DCM) and critical conduction mode (CRM). Both modes can realize ZCS turn-on without diode reverse recovery so that low switching losses and low-cost diode utilizations are obtainable. Among various boost-family PFC topologies, three-level boost (TLB) converter has generated considerable research interest in high-voltage high-power applications. It is mainly due to the fact that the topology can have halved component voltage stresses, improved waveform qualities and electromagnetic interference (EMI) from phase interleaved continuous conduction mode (CCM) operations, compared to other two-level boost PFC converters. On the other hand, in the field of universal-line low-power applications, TLB PFC has been thoroughly out of focus since doubled component counts and increased control complexity than two-level topologies are practical burden for the low-cost systems. However, recent researches on TLB PFC with ZCS control schemes have found that cost-competitiveness of the topology is actually comparable to two-level boost PFC converters because the halved component voltage stresses enable usage of low voltage-rating components of which unit prices are cheaper than higher-rating ones. Based on the justification, researches on ZCS control schemes for TLB PFC have been conducted to get enhanced waveform qualities and performance factors. Following the research stream, a three-level current modulation scheme that can be adopted in both DCM and CRM is proposed in Chapter 2 of this dissertation. Main concept of the proposed current modulation is additional degree-of-freedom in current-slope shaping by differentiating on-times of two active switches, which cannot be found from any other single-phase boost-derived PFC topologies. Using the multilevel feature, proposed operations in one switching period consist of three steps: common-switch on-time, single-switch on-time and common-switch off-time. The single-switch on-time step is key design factor of the proposed modulation that can be utilized either in fixed or adjustable form depending on control purpose. Based on the basic modulation concept, three-level CRM control scheme, adjustable three-level DCM control scheme, and spread-spectrum frequency modulation (SSFM) with adjustable three-level DCM scheme are proposed in Chapter 3–5, respectively. In each chapter, implemented control scheme aims to improve different performance factors. In Chapter 3, the proposed three-level CRM scheme uses increased single-switch on-time period to reduce peak inductor current and magnitude of variable switching frequency. It is generally accepted fact that CRM operations suffer from high switching losses and poor efficiency at light load due to considerable increment of switching frequency. Thus, efficiency improvement effect by the proposed CRM scheme becomes remarkable as load condition goes lighter. In experimental verifications, maximum improvement is measured by 1.2% at light load (20%) and overall efficiency is increased by at least 0.4% all over the load range. In Chapter 4, three-level DCM control scheme adopts adjustable single-switch on-time period in fixed switching-frequency framework. The purpose of adjustable control scheme is to widen the length of non-zero inductor current period as much as possible so that discontinued current period and high peak current of DCM operations can be minimized. Experiment results show that, compared to conventional two-level DCM control, full-load peak inductor currents are reduced by 20.2% and 17.1% at 110 and 220 Vrms input voltage conditions, respectively. Moreover, due to turn-off switching energy decrements by the turn-off current reductions, efficiency is also improved by at least 0.4% regardless of input voltage and load conditions. In Chapter 5, a downward SSFM technique is developed first for DCM operations of boosting PFC converters including two-level topologies. This chapter aims to achieve significant reduction of high differential-mode (DM) EMI amplitudes from DCM operations, which is major drawback of DCM control. By using the simple linearized frequency modulation, peak DM EMI noise at full load condition is reduced by 12.7 dBμV than conventional fixed-frequency DCM control. On top of the proposed SSFM, the adjustable three-level DCM control scheme in Chapter 4 is adopted to get further reductions of EMI noises. Experimental results prove that the collaborations of SSFM and adjustable DCM scheme reduce the EMI amplitudes further by 2.5 dBμV than the result of SSFM itself. The reduced EMI amplitudes are helpful to design input EMI filter with higher cut-off frequency and smaller size. Different from two-level boosting PFC converters, TLB PFC topology has two output capacitors in series and inherently suffers from voltage unbalancing issue, which can be noted as topological trade-off. In Chapter 6, two simple but effective voltage balancing schemes are introduced. The balancing schemes can be easily built into the proposed ZCS control schemes in Chapter 3–5 and experimental results validate the effectiveness of the proposed balancing principles. For all the proposed control schemes in this dissertation, detailed operation principles, derivation process of key equations, comparative analyses, implementation method with digital controller and experimental verifications with TLB PFC prototype are provided. / Doctor of Philosophy / Electronic-based devices and loads have been essential parts of modern society founded on rapid advancements of information technologies. Along with the progress, power supplying and charging of electronic products become routinized in daily lives, but still remain critical requisites for reliable operations. In many power-electronics-based supplying systems, ac-dc power-factor correction (PFC) circuits are generally located at front-end to feed back-end loads from universal ac-line sources. Since PFC stages have a key role in regulating ac-side current quality and dc-side voltage control, the importance of PFC performances cannot be emphasized enough from entire system point of view. Thus, advanced control schemes for PFC converters have been developed in quantity to achieve efficient operations and competent power qualities such as high power factor, low harmonic distortions and low electromagnetic interferences (EMI) noises. In this dissertation, a sort of PFC topologies named three-level boost (TLB) converter is chosen for target topology. Based on inherent three-level waveform capability of the topology, multiple zero-current switching (ZCS) control schemes are proposed. Compared to many conventional two-level PFC topologies, TLB PFC can provide additional degree-of-freedom to current modulation. The increased control flexibility can realize improvements of various waveform qualities including peak current stress, switching frequency range, harmonics and EMI amplitude. From the experimental results in this dissertation, improvements of waveform qualities in TLB PFC with the proposed schemes are verified with comparison to two-level current control schemes; in terms of efficiency, the results show that TLB PFC with the proposed schemes can have similar converter efficiency with conventional two-level boost converter in spite of increased component counts in the topology. Further, the proposed three-level control schemes can be utilized in adjustable forms to accomplish different control objectives depending on system characteristics and applications. In each chapter of this dissertation, a novel control scheme is proposed and explained with details of operation principle, key equations and digital implementation method. All the effectiveness of proposals and analyses are validated by a proper set of experimental results with a TLB PFC prototype.

One of the requirements for the next generation of power supplies for distributed power systems (DPSs) is to achieve high power density with high efficiency. In the traditional front-end converter based on the two-stage approach for high-power three-phase DPSs, the DC-link voltage coming from the power factor correction (PFC) stage penalizes the second-stage DC/DC converter. This DC/DC converter not only has to meet the characteristics demanded by the load, but also must process energy with high efficiency, high reliability, high power density and low cost. To meet these requirements, approaches such as the series connection of converters and converters that reduce the voltage stress across the main devices have been proposed. In order to improve the characteristics of these solutions, this dissertation proposes high-efficiency, high-density DC/DC converters for high-power high-voltage applications. In the first part of the dissertation, a DC/DC converter based on a three-level structure and operated with pulse width modulation (PWM) phase-shift control is proposed. This new way to operate the three-level DC/DC converter allows soft-switching operation for the main devices. Zero-voltage switching (ZVS) and zero-voltage and zero-current switching (ZVZCS) soft-switching techniques are studied, analyzed and compared in order to improve the characteristics of the proposed converter. This results in a series of ZVS and ZVZCS three-level DC/DC converters for high-power high-voltage applications. In all cases, results from 6kW prototypes operating at 100 kHz are presented. In addition, with the ultimate goal of improving the power density of the DC/DC converter, a study of several resonant DC/DC converters that can operate at higher switching frequencies is presented. From this study, a three-element ZVS three-level resonant converter for applications with wide input voltage and load variations is proposed. Experimental results at 745 kHz obtained without penalizing the efficiency of the PWM approaches are presented. The second part of the dissertation proposes a quasi-integrated AC/DC three-phase converter that aims to reduce the complexity and cost of the traditional two-stage front-end converter. This converter improves the complexity/low-efficiency tradeoff characteristics evident in the two-stage approach and previous integrated converters. The principle of operation for the converter is analyzed and verified on a 3kW experimental prototype. / Ph. D.

With the development of information technology, power management for telecom and computer applications become a large market for power supply industries. To meet the performance and reliability requirement, distributed power system (DPS) is widely adopted for telecom and computer systems, because of its modularity, maintainability and high reliability. Due to limited space and increasing power consumption, power supplies for telecom and server systems are required to deliver more power with smaller volume. As the key component of DPS system, front-end AC/DC converter is under the pressure of continuously increasing power density. For conventional industry practices, some limitations prevents front-end converter meeting the power density requirement. In this dissertation, different techniques have been investigated to improve power density of front-end AC/DC converters. For PFC stage, at low switching frequency, PFC inductor size is large and limits the power density. Although increasing switching frequency can dramatically reduce PFC inductor size, EMI filter size might be larger at higher switching frequency because of the change of noise spectrum. Since the relationship between EMI filter size and PFC switching frequency is unclear for industry, PFC circuits always operate with switching frequency lower than 150 kHz. Based on the EMI filter design method, together with a simple EMI noise prediction model, relationship between EMI filter corner frequency and PFC switching frequency was revealed. The analysis shows that switching frequency of PFC circuit should be higher than 400 kHz, so that both PFC inductor and EMI filter size can be reduced. Although theoretical analysis and experimental results verify the benefits of high switching frequency PFC, it is essential to find a suitable topology that allows high switching frequency operation while maintains high efficiency. Three PFC topologies, single switch PFC, three-level PFC with range switch and dual Boost PFC, were evaluated with analysis and experiments. By using advanced semiconductor devices, together with proposed control methods, these topologies could achieve high efficiency at high switching frequency. Thus, the benefits of high frequency PFC can be realized. In front-end converter, large holdup time capacitor size is another barrier for power density improvement. To meet the holdup time requirement, bulky holdup time capacitor is normally used to provide energy during holdup time. Holdup time capacitor requirement can be reduced by using wider input voltage range DC/DC converte. Because LLC resonant converter can realized with input voltage range without sacrificing its normal operation efficiency, it becomes an attractive solution for DC/DC stage of front-end converters. Moreover, its small switching loss allows it operating at MHz switching frequency and achieves smaller passive component size. However, lack of design methodology makes the topology difficult to be implemented. An optimal design methodology for LLC resonant converter has been developed based on the analysis on the circuit during normal operation condition and holdup time. The design method is verified by a 1 MHz switching frequency LLC resonant converter with 76W/in3 power density. When front-end converter operates at high switching frequency, negative effects of circuit parasitics become more pronounced. By integrating active devices together with their gate drivers, Active Integrated power electronics module (IPEM) can largely reduce circuit parasitics. Therefore, switching loss and voltage stress on switching devices can be reduced. Moreover, IPEM concept can be extended into passive integration and EMI filter integration By using this power integration technology, power density and circuit performance of front-end converter can be improved, which is verified by theoretical analysis and experimental results. / Ph. D.

Afin de dépasser la limite d'échelle, il existe une solution innovante qui permet de fabriquer des structures multi-grilles. Ainsi, un NMOSFET composé de trois grilles indépendantes fabriquées dans la technologie CMOS. En dehors de leur forme, géométrique, le transistor multi-grille est similaire à une structure classique. Une multi-grille NMOSFET peut être fabriquée par l'intégration de tranchées de polysilicium. Ces tranchées sont utilisées dans diverses applications telles que les mémoires DRAM, électronique de puissance ou de capteurs d'image. Les capteurs d'image présentent le problème des charges parasites entre les pixels, appelées diaphonie. Les tranchées sont l'une des solutions qui réduisent ce phénomène. Ces tranchées assurent l'isolation électrique sur toute la matrice des pixels. Nous avons étudié ses caractéristiques en utilisant des mesures I-V, méthode du split C-V et de pompage de charge à deux et à trois niveaux. Son multi-seuil caractéristique a été vérifié. Nous n'avons observé aucune dégradation significative de ces caractéristiques grâce à l'intégration des tranchées. La structure a été simulée par la méthode des éléments finis en 3D via le logiciel TCAD. Ses caractéristiques électriques ont été simulées et confrontées avec les résultats obtenus à partir de mesures électriques. La tension de seuil et la longueur de canal effective ont été extraites. Sa mobilité effective et les pièges de l'interface Si/SiO2 ont également été simulés ou calculés. En raison des performances électriques satisfaisantes et d'un bon rendement, nous avons remarqué que ce dispositif est une solution adéquate pour les applications analogiques grâce aux niveaux de tension multi-seuil / One of the recent solutions to overcome the scaling limit issue are multi-gate structures. One cost-effective approach is a three-independent-gate NMOSFET fabricated in a standard bulk CMOS process. Apart from their shape, which takes advantage of the three-dimensional space, multi gate transistors are similar to the conventional one. A multi-gate NMOSFET in bulk CMOS process can be fabricated by integration of polysilicon-filled trenches. This trenches are variety of the applications for instance in DRAM memories, power electronics and in image sensors. The image sensors suffer from the parasitic charges between the pixels, called crosstalk. The polysilicon - filled trenches are one of the solution to reduce this phenomenon. These trenches ensure the electrical insulation on the whole matrix pixels. We have investigated its characteristics using l-V measurements, C-V split method and both two- and three-level charge pumping techniques. Tts tunable-threshold and multi-threshold features were verified. Tts surface- channel low-field electron mobility and the Si/SiO2 interface traps were also evaluated. We observed no significant degradation of these characteristics due to integration of polysilicon-filled trenches in the CMOS process. The structure has been simulated by using 3D TCAD tool. Tts electrical characteristics has been evaluated and compared with results obtained from electrical measurements. The threshold voltage and the effective channel length were extracted. Tts surface-channel low-field electron mobility and the Si/SiO2 interface traps were also evaluated. Owing to the good electrical performances and cost-effective production, we noticed that this device is a good aspirant for analog applications thanks to the multi-threshold voltages

La presente tesis estudia, propone y realiza sus principales aportaciones en el campo del control para el convertidor CC/CA de tres niveles, sobre la topología denominada Neutral-Point-Clamped, aunque se puede extender a otras topologías y/o número de niveles. Se presenta una metodología de modelado que emplea funciones de conmutación de fase, el operador de promediado y la transformación D-Q, tal que los modelos obtenidos en el dominio D-Q contienen una información completa sobre la dinámica del sistema. La estrategia de conmutación se puede entender como una extensión de la estrategia PWM senoidal de dos a tres niveles. Esta estrategia es simple y no realiza el control de ninguna de las variables del sistema. En esta tesis, el controlador se encarga de regular todas las variables del sistema, incluido el equilibrio del bus de continua. Este es un enfoque diferente del convencional, donde el equilibrio del bus de continua se consigue mediante la elección adecuada de los estados redundantes del convertidor en la estrategia de conmutación, mientras que el resto de variables se regulan a través del controlador. Para la realización del controlador, se propone la técnica de control lineal multivariable LQR (Linear Quadratic Regulator), complementada con la técnica de control no lineal adaptativo denominada programación de ganancia (Gain Scheduling). Se presenta, además, una metodología de cálculo del controlador. Este control es versátil, abierto y adaptable. En cualquier caso, el controlador se puede adaptar a las necesidades concretas de cada aplicación. El cálculo del controlador se realiza mediante simulación con MatLab-Simulink. Los modelos matemáticos que emplean las funciones de conmutación del convertidor son aquellos que ofrecen un mejor compromiso entre velocidad de simulación y precisión. Para validar el control propuesto, se ha diseñado y construido un equipo experimental donde el controlador se ha mostrado aplicable, útil y eficaz en la regulación de las distintas cargas y aplicaciones experimentadas, incluso con carga no lineal, bajo diferentes condiciones de trabajo y variables a controlar, tanto en régimen permanente como en procesos transitorios. La rapidez y calidad de la respuesta transitoria es comparable a la de otros sistemas de control publicados. Es especialmente interesante el excelente control conseguido del equilibrio del bus de continua. Además, la robustez del control permite cancelar el error estacionario aunque diferentes parámetros del sistema presenten desviaciones significativas respecto los valores esperados. El uso de la programación de ganancia junto con la técnica LQR se ha mostrado muy efectivo, puesto que permite realizar diferentes tipos de control. Se ha comprobado la congruencia entre simulaciones y resultados experimentales obtenidos, lo que valida los modelos de simulación empleados y el proceso de diseño del controlador mediante simulación. / This dissertation study, propose and carry out the main contributions in the field of three-level inverter control, using the topology Neutral-Point-Clamped, although results can be extended to other topologies and/or number of levels. A procedure for modelling is presented, based on line-switching functions, moving average operator and D-Q transformation. Then, the obtained models in D-Q frame contain complete information about system dynamics. Switching strategy is simple and can be considered as an extension of two-level sinusoidal PWM to three level. The system variables are not controlled by the switching strategy. In this work, all the system variables are controlled by the regulator, including DC-link balance. This control approach is different than the conventional one, where DC-link balance is achieved by means of a proper selection of redundant states in the switching strategy, and the other variables are controlled by the regulator. The regulator is based on the multivariable linear control technique LQR (Linear Quadratic Regulator), in combination with the non-linear adaptive control technique Gain Scheduling. Moreover, a methodology for the calculation of the controller is presented. This controller is versatile, open and adaptable. However, the controller can be built depending on the concrete specifications of each application. The controller is calculated by means of simulation using MatLab-Simulink. The mathematical models based on the switching functions of the converter give the best trade-off between simulation speed and precision. In order to validate the proposed controller, an experimental prototype has been designed and implemented. Experimental results show that the controller is useful and effective for the regulation of different loads and applications, even with non-linear loads, different operation points and variables to control, in steady-state and transitory operation. Dynamic response speed and quality are similar to other control systems in the literature. The DC-link balance control achieved is specially interesting. Furthermore, steady-state error is cancelled due to the robustness of the controller, even though significant deviation of different system parameters are present. The use of Gain-Scheduling in combination with LQR is effective, allowing the calculation of regulators with different control strategies. Good agreement between simulations and experimental results has been found. This result validates simulation models and the design method for the controller, based on simulations.

In this Master’s thesis, we have focused on the description of three-level quantum systems through master equations for their density matrix, involving a recently proposed non-linear thermodynamic one. The first part is focused on a three-level system interacting with two heat baths, a hot and a cold one. We investigated the rate of heat flow from the hot to the cold bath through the quantum system, and how the steady-state is approached. Additional calculations here refer to the rate of entropy production and the evolution of all elements of the density matrix of the system from an arbitrary initial state to their equilibrium or steady-state value. The results are compared against those of a linear, Lindblad-type master equation designed so that for a quantum system interacting with only one heat bath, the same final Gibbs steady state is attained. In the second part of this thesis, we focus on the electromagnetically induced transparency (EIT), a phenomenon typically achievable only in atoms with specific energy structures. For a three level system (to which the present study has focused), for example, EIT requires two dipole allowed transitions (the 1-3 and the 2-3) and one forbidden (the 1-2). The phenomenon is observed when a strong laser (termed the control laser) is tuned to the resonant frequency of the upper two levels. Then, as a weak probe laser is scanned in frequency across the other transition, the medium is observed to exhibit both: a) transparency at what was the maximal absorption in the absence of the coupling field, and b) large dispersion effects at the atomic resonance. We discuss the Hamiltonian describing the phenomenon and we present results from two types of master equations: a) an empirically modified Von-Neumann one allowing for decays from each energy state, and b) a typical Lindblad one, with time-dependent operators. In the first case, an analytical solution is possible, which has been confirmed through a direct solution of the full master equation. In the second case, only numerical results can be obtained. We present and compare results from the two master equations for the susceptibility of the system with respect to the probe field, and we discuss them in light also of available experimental data for this very important phenomenon. / Η παρούσα εργασία επικεντρώνεται στην περιγραφή των κβαντικών συστημάτων τριών καταστάσεων μέσω εξισώσεων master για την μήτρα πυκνότητας πιθανότητάς τους (density matrix), συμπεριλαμβάνοντας μία πρόσφατα προτεινόμενη μη-γραμμική θερμοδυναμική εξίσωση. Το πρώτο μέρος εστιάζει σε ένα σύστημα τριών καταστάσεων το οποίο βρίσκεται σε αλληλεπίδραση με δύο λουτρά θερμότητας, ένα θερμό και ένα ψυχρό. Εξετάζεται ο ρυθμός ροής θερμότητας από το θερμό προς το ψυχρό λουτρό μέσω του κβαντικού συστήματος, και με ποιον τρόπο επιτυγχάνεται η μόνιμη κατάσταση. Επιπλέον υπολογισμοί αναφέρονται στον ρυθμό παραγωγής της εντροπίας και στην εξέλιξη όλων των στοιχείων της μήτρας πυκνότητας πιθανότητας από μία τυχαία αρχική κατάσταση προς την ισορροπία ή τη μόνιμη κατάσταση. Τα αποτελέσματα παρουσιάζονται συγκριτικά με εκείνα μιας γραμμικής, τύπου Lindblad master εξίσωσης, κατάλληλα σχεδιασμένης ώστε στην ειδική περίπτωση ενός κβαντικού συστήματος σε αλληλεπίδραση με ένα λουτρό θερμότητας επιτυγχάνεται η ίδια τελική μόνιμη κατάσταση Gibbs. Στο δεύτερο μέρος, εστιάζουμε στην ηλεκτρομαγνητικά επαγόμενη διαφάνεια (electromagnetically induced transparency (EIT)), ένα φαινόμενο το οποίο τυπικά είναι εφικτό μόνο σε άτομα με ειδικές ενεργειακές δομές. Για ένα σύστημα τριών καταστάσεων (στο οποίο επικεντρώνεται η παρούσα εργασία), για παράδειγμα, το ΕΙΤ απαιτεί δύο διπολικά επιτρεπτές μεταβάσεις (την 1-3 και την 2-3) και μία απαγορευμένη (την 1-2). Το φαινόμενο παρατηρείται όταν ένα ισχυρό laser (το αποκαλούμενο ως control laser) συντονίζεται στη συχνότητα των δύο άνω ενεργειακών σταθμών. Τότε, καθώς ένα ασθενές probe laser ανιχνεύεται με συχνότητα όμοια με της άλλης επιτρεπόμενης μετάβασης, το μέσο παρατηρείται να εμφανίζει τα εξής: α) διαφάνεια στο σημείο μέγιστης απορρόφησης απουσία του control πεδίου, και β) έντονα φαινόμενα διασποράς στον ατομικό συντονισμό. Θα συζητήσουμε τη Χαμιλτονιανή που περιγράφει το φαινόμενο και θα παρουσιάσουμε αποτελέσματα από δύο εξισώσεις master: α) μία εμπειρική τροποποιημένη Von-Neumann εξίσωση επιτρέποντας τις απώλειες από κάθε ενεργειακή κατάσταση, και β) μία τυπική Lindblad εξίσωση, με χρόνο-εξαρτώμενους τελεστές. Στην πρώτη περίπτωση, είναι πιθανή η εύρεση μιας αναλυτικής λύσης, η οποία έχει επιβεβαιωθεί μέσω μιας άμεσης (direct) λύσης της πλήρους εξίσωσης master. Στη δεύτερη περίπτωση, μπορούν να ληφθούν μόνο αριθμητικά αποτελέσματα. Παρουσιάζονται και συγκρίνονται τα αποτελέσματα που ελήφθησαν από τις δύο master εξισώσεις και αφορούν την επιδεκτικότητα (susceptibility) του συστήματος σε σχέση με το probe πεδίο, και τέλος συζητιούνται σε σχέση με διαθέσιμα πειραματικά δεδομένα γι’ αυτό το πολύ σημαντικό φαινόμενο.

In recent years, the research approach known as Resilience Engineering (RE) has offered a promising new way of understanding safety-critical organizations, but less in the way of empirical methods for analysis. In this master’s thesis, an extensive comparison was made between RE and two different research approaches on cognitive systems: Distributed Cognition (DC) and Cognitive Systems Engineering (CSE) with the aim of exploring whether these approaches can contribute to the analysis and understanding of resilience. In addition to a theoretical comparison, an ethnographic healthcare case study was conducted, analyzing the patient safety at a pediatric emergency department using the Three-Level Analytical Framework from DC and the Extended Control Model from CSE, then conducting an RE analysis based on the former two analyses. It was found that while the DC and CSE approaches can explain how an organization adapts to current demands, neither approach fully addresses the issue of future demands anticipation, central to the RE perspective. However, the CSE framework lends itself well as an empirical ground providing the entry points for a more thoroughgoing RE analysis, while the inclusion of physical context in a DC analysis offers valuable insights to safety-related issues that would otherwise be left out in the study of resilience.

Le travail de cette thèse apporte une contribution aux méthodes de réglage de la tension dans les réseaux électriques. Il s’agit de fournir au réseau la puissance active et surtout la puissance réactive nécessaire pour réguler la tension et aboutir à un système équilibré vue du côté source. Ces puissances sont extraites d’une source d’energie renouvelable : une attention particulière a été portée à l’énergie éolienne raccordée au réseau à travers la Machine Asynchrone à Double Alimentation (MADA) pilotée par des convertisseurs statiques. Le système de contrôle le plus répandu des éoliennes est basé principalement sur la technique d’extraction du maximum de puissance. Cependant, cette technique limite la mise en oeuvre deservices auxiliaires, telle que la participation des éoliennes au réglage de la tension dans le réseau électrique. Pour cela, une nouvelle méthode d’extraction du coefficient de puissance optimal, permettant d’améliorer la participation de la MADA à la régulation de la tension dans le réseau (compensation de la puissance réactive et du déséquilibre), a été développée. Le convertisseur multiniveaux à structure NPC (Neutral Point Clamped) raccordant l’énergie renouvelable au réseau a été étudié. La commande prédictive assurant simulatnément l’amélioration du facteur de puissance, l’équilibrage du réseau électrique et du bus continu du convertisseur NPC a été proposée. Ensuite, l’application de cette commande prédictive a été elargie en lui attribuant plusieurs objectifs : amélioration du facteur de puissance avec équilibrage du réseau, équilibrage du bus continu, minimisation des pertes par commutation et réduction de la tension de mode commun. La minimisation des pertes a été obtenue en proposant une nouvelle stratégie qui consiste à exploiter les datasheets constructeurs donnant l’évolution de l’énergie dissipée durant la commutation en fonction du courant. Ces courbes expérimentales ont été transformées en modèlesmathématiques implémentés dans la commande prédictive. Les résultats de simulation et expérimentaux sont présentés pour évaluer les performances de la méthode proposée. / The work in this research thesis presents a contribution to voltage regulation in electrical networks. By considering adequate active and reactive powers injection into the grid, voltage control and load balancing are provided. These powers are generated from a grid connected renewable energy conversion system : a special attention was paid to the Wind Energy ConversionSystem (WECS) based on Doubly-Fed Induction Generator (DFIG).The typical control strategy for WECS is the maximum power coefficient tracking method. However, this method limits desirable ancillary power services, such as the participation of wind turbines in voltage regulation in the power grid. Therefore, a new method that derives the optimal power coefficient enhancing the participation of WTS in voltage regulation in the network (reactive and unbalanced power compensation), has been developed. The multilevel NPC (Neutral Point Clamped) converter, used for grid interface connection of renewable energy sources systems, has been studied. A predictive control method for the three-level NPC converter, capable of simultaneously compensating the problems of : DC link capacitors voltage balancing, load balancing and power factor correction in the power system, has been proposed. Then, the application of this predictive control was extended to simultaneously achieve multiple objectives: load balancing with power factor correction in the network, DC link capacitors voltage balancing, switching losses minimization and common mode voltage reduction. The switching losses minimization was obtained by proposing a new strategy which consists on exploiting the manufacturer datasheets that gives the evolution of the switching loss energy in function of the circulating current. The experimental curves of the datasheet are expressed in a mathematical model implemented in the predictive control. Simulation and experimental results are presented to evaluate the performance of the proposed method.