Dans ce mémoire, nous avons étudié les convertisseurs d’interface permettant l’interconnexion d’une source basse tension non linéaire et d’un bus DC moyenne tension. La source choisie, pour l’étude, était une pile à combustible de type PEM. La structure de puissance retenue correspondant à la mise en cascade d’un convertisseur entrelacé en entrée et d’un convertisseur trois niveaux en sortie. Afin de dimensionner au mieux le convertisseur global, nous avons proposé un modèle analytique permettant de connaitre l’ensemble des pertes dans le système en fonction du point de fonctionnement et de ses paramètres. Nous avons montré que l’ensemble des pertes dans le convertisseur peut être modélisé par deux résistances non linéaires dont l’estimation est possible à partir des modèles moyens du convertisseur. Une commande basée sur le concept de platitude des systèmes différentiels a été utilisée pour assurer les différentes contraintes du système tout en obtenant des propriétés dynamiques élevées en asservissement et en régulation. Dans la dernière partie du mémoire, nous nous sommes intéressés aux solutions permettant de satisfaire les contraintes sur le taux d’ondulation de courant en entrée du convertisseur. Nous avons proposé et dimensionné une nouvelle structure de convertisseur permettant de supprimer les ondulations de courant générées par le convertisseur de puissance. Ce filtre actif se connecte en parallèle avec le convertisseur de puissance. Des résultats expérimentaux ont permis de montrer que le taux d’ondulation de courant d’un convertisseur élévateur a été réduit, le taux d’ondulation de courant passant de 23.3% à 1.9% / In this thesis, we studied interface converters enabling the interconnection of a low voltage nonlinear source and a medium voltage DC bus. The source selected for the study was a fuel cell PEM. The chosen power architecture corresponds to a cascaded structure constituted with an interleaved Boost converter at input stage and a three-level Boost converter at output stage. To design the converter, we proposed an analytical model to know the total losses in the system according to the operating point and its parameters. We showed that all losses in the converter can be modeled by two nonlinear resistors. An estimation of these resistors, deduced from average model of the converter, is developed. A control based on the concept of differential systems flatness has been used for the proposed converter structure. It allows taking into account the different system constraints. High dynamic properties as regard to external perturbations or parameters variations are achieved. In the last part of the thesis, we investigate solutions to respect the constraints on the rate of input current ripple. We propose a new active filtering converter connected in parallel with the power one. We have shown that the ripple current of a boost converter was reduced, the ripple current being reduced from 23.3% to 1.9%

The thesis aims at building an experimental setup for conducting the boundary ejection and resonance ejection experiments on wide variety of ion trap mass analyzers. The experimental setup has two parts namely power electronics circuits and mechanical assembly. The focus of the thesis is on the electronics hardware which provides various power sources required for the operation of ion trap mass spectrometer. The electronics circuits discussed in the thesis have better performance, flexibility and ruggedness compared to the existing setup. The traditional power supplies used in ion trap mass spectrometers are all linear supplies. But one major drawback of these supplies is the high power dissipation and consequently, the power efficiency degrades. We are trying to introduce switch mode power supplies to reduce the power dissipation loss and eventually increase the power efficiency. In the course of the work the following power supplies have been developed. The supplies are - 1.Constant current source, 2.Filament base, 3.gating power supply and pulsing circuit, 4.High voltage DC power supply and 5. High voltage RF generator.

The thesis consists of an introduction and four appended papers. In the introduction we give an overview of pulse-modulated systems and provide a few examples of such systems. Furthermore, we introduce the so-called dynamic phasor model which is used as a basis for analysis in two of the appended papers. We also introduce the harmonic transfer function and finally we provide a summary of the appended papers. The first paper considers stability analysis of a class of pulse-width modulated systems based on a discrete time model. The systems considered typically have periodic solutions. Stability of a periodic solution is equivalent to stability of a fixed point of a discrete time model of the system dynamics. Conditions for global and local exponential stability of the discrete time model are derived using quadratic and piecewise quadratic Lyapunov functions. A griding procedure is used to develop a systematic method to search for the Lyapunov functions. The second paper considers the dynamic phasor model as a tool for stability analysis of a general class of pulse-modulated systems. The analysis covers both linear time periodic systems and systems where the pulse modulation is controlled by feedback. The dynamic phasor model provides an $\textbf{L}_2$-equivalent description of the system dynamics in terms of an infinite dimensional dynamic system. The infinite dimensional phasor system is approximated via a skew truncation. The truncated system is used to derive a systematic method to compute time periodic quadratic Lyapunov functions. The third paper considers the dynamic phasor model as a tool for harmonic analysis of a class of pulse-width modulated systems. The analysis covers both linear time periodic systems and non-periodic systems where the switching is controlled by feedback. As in the second paper of the thesis, we represent the switching system using the L_2-equivalent infinite dimensional system provided by the phasor model. It is shown that there is a connection between the dynamic phasor model and the harmonic transfer function of a linear time periodic system and this connection is used to extend the notion of harmonic transfer function to describe periodic solutions of non-periodic systems. The infinite dimensional phasor system is approximated via a square truncation. We assume that the response of the truncated system to a periodic disturbance is also periodic and we consider the corresponding harmonic balance equations. An approximate solution of these equations is stated in terms of a harmonic transfer function which is analogous to the harmonic transfer function of a linear time periodic system. The aforementioned assumption is proved to hold for small disturbances by proving the existence of a solution to a fixed point equation. The proof implies that for small disturbances, the approximation is good. Finally, the fourth paper considers control synthesis for switched mode DC-DC converters. The synthesis is based on a sampled data model of the system dynamics. The sampled data model gives an exact description of the converter state at the switching instances, but also includes a lifted signal which represents the inter-sampling behavior. Within the sampled data framework we consider H-infinity control design to achieve robustness to disturbances and load variations. The suggested controller is applied to two benchmark examples; a step-down and a step-up converter. Performance is verified in both simulations and in experiments. / QC 20100628

Modelling and simulation are essential ingredients of the analysis and design process in power electronics. It helps a design engineer gain an increased understanding of circuit operation. Accordingly, for a set of specifications given, the designer will choose a particular topology, select component types and values, estimate circuit performance etc. Typically hierarchical modelling, analysis and simulation rather than full detailed simulation of the system provides a crucial insight and understanding. The combination of these insights with hardware prototyping and experiments constitutes a powerful and effective approach to design. Obtaining the mathematical model of the power electronic systems is a major task before any analysis or synthesis or simulation can be performed. There are circuit oriented simulators which uses inbuilt mathematical models for components. Simulation with equation solver needs mathematical models for simulation which are trimmed according to user requirement. There are various methods in the literature to obtain these mathematical models. However, the issues of multi-domain system modelling and causality of the energy variables are not sufficiently addressed. Further, specifically to power converter systems, the issue of switching power models with fixed causality is not addressed. Therefore, our research focuses on obtaining solutions to the above using relatively untouched bond graph method to obtain models for power electronic systems. The power electronic system chosen for the present work is Switched Mode Power Converters (SMPC’s) and in particular PWM DC-DC converters. Bond graph is a labelled and directed graphical representation of physical systems. The basis of bond graph modelling is energy/power flow in a system. As energy or power flow is the underlying principle for bond graph modelling, there is seamless integration across multiple domains. As a consequence, different domains (such as electrical, mechanical, thermal, fluid, magnetic etc.) can be represented in a unified way. The power or the energy flow is represented by a half arrow, which is called the power bond or the energy bond. The causality for each bond is a significant issue that is inherently addressed in bond graph modelling. As every bond involves two power variables, the decision of setting the cause variable and the effect variable is by natural laws. This has a significant bearing in the resulting state equations of the system. Proper assignment of power direction resolves the sign-placing problem when connecting sub-model structures. The causality will dictate whether a specific power variable is a cause or the effect. Using causal bars on either ends of the power bond, graphically indicate the causality for every bond. Once the causality gets assigned, bond graph displays the structure of state space equations explicitly. The first problem we have encountered in modelling power electronic systems with bond graph is power switching. The essential part of any switched power electronic system is a switch. Switching in the power electronic circuits causes change in the structure of the system. This results in change in dynamic equations of the circuit according to position of the switch. We have proposed the switched power junctions (SPJ) to represent switching phenomena in power electronic systems. The switched power junctions are a generalization of the already existing 0-junction and 1-junction concepts of the bond graph element set. The SPJ’s models ideal switching. These elements maintain causality invariance for the whole system for any operational mode of the system. This means that the state vector of the resulting state equation of the system does not change for any operating mode. As SPJs models ideal power switching, the problem of stiff systems and associated numerical stability problems while simulating the system is eliminated. Further, it maintains one to one correspondence with the physical system displaying all the feasible modes of operation at the same time on the same graph. Using these elements, the switched mode power converters (SMPC's) are modelled in bond graph. Bond graph of the converter is the large signal model of the converter. A graphical procedure is proposed that gives the averaged large signal, steady state and small signal ac models. The procedure is suitable for the converters operating in both Continuous Conduction Mode (CCM) and in Discontinuous Conduction Mode (DCM). For modelling in DCM, the concept of virtual switch is used to model the converter using bond graph. Using the proposed method, converters of any complexity can be modelled incorporating all the advantages of bond graph modelling. Magnetic components are essential part of the power electronic systems. Most common parts are the inductor, transformer and coupled inductors which contain both the electric and magnetic domains. Gyrator-Permeance approach is used to model the magnetic components. Gyrator acts as an interface between electric and magnetic domain and capacitor model the permeance of the magnetic circuits. Components like inductor, tapped inductor, transformer, and tapped transformer are modelled. Interleaved converters with coupled inductor, zero ripple phenomena in coupled inductor converters as well as integrated magnetic Cuk converter are also modelled. Modelling of integrated magnetic converters like integrated magnetic forward converter, integrated magnetic boost converter are also explored. To carry out all the simulations of proposed bond graph models, bond graph toolbox is developed using MATLAB/SIMULINK. The MATLAB/SIMULINK is chosen since it is general simulation platform widely available. Therefore all the analysis and simulation can be carried out using facilities available in MATLAB/SIMULINK. Symbolic equation extraction toolbox is also developed which extracts state equations from bond graph model in SIMULINK in symbolic form.

In the fast growing field of Telecommunications, the back up DC power supply plays a vital role in powering the telecom equipment. This DC power supply is a combination of AC-DC Rectifier coupled with a battery bank to support the load when AC input is not available. Figures 0.1 and 0.2 show the line diagram of the DC power supply. The power supply is the most critical element in a telecom installation and it should be highly reliable in order to have un-interrupted service. (Fig) Besides reliability, power density and cost are the driving forces behind the success of a power supply in the market. Off late, the reach of telecom in the society is very wide covering remote villages and major metros. Given this environment, the power supply is exposed to extreme input conditions. It is desirable to design the power supply capable of withstanding wide AC input conditions. Another advantage is that the rectifier unit will keep the battery charged so that the battery will have long life. This thesis is aimed at designing a 1400W (56V/25A) telecom power supply, keeping in view of the issues expressed above. The aim is to design a Switched Mode Rectifier (SMR) that tolerate wide input voltage variations (90Vac to 300Vac). In addition, the design covers unity input power factor, high efficiency (> 90%), high power density ( ), parallel operation and low cost ( ). Chapter 1 of this thesis covers the context and motivation of the work. Chapter 2 presents the design issues pertaining to power supplies. The normalized description of the power converters is presented. Such a description enables one to compare several circuit topologies in order to make effective design decisions. In a similar way the effectiveness of the switches and mgnetics are presented to enable design decisions in the output stage of the rectifier. Chapter 3 presents the design of the 1400W telecom power supply, keeping in view of the stated specifications. The performance results of the converter are presented in Chapter 4. All the design goals have been met. The design exercise has also given insights into possible further improvements. Contributions from this work and course of future development work are indicated in the concluding chapter.

Boost dc-to-dc converters have very good source interface properties. The input inductor makes the source current smooth and hence these converters provide very good EMI performance. On account of this good property, the boost converter is also the preferred converter for off-line UPF rectifiers. One of the issues of concern in these converters is the large size of the storage capacitor on the dc link. The boost converter suffers from the disadvantage of discontinuous current injected to the load. The size of the capacitor is therefore large. Further, the ripple current in the capacitor is as much as the load current; hence the ESR specification of the tank capacitor is quite demanding. This is specially so in the emerging application areas of automotive power conversion, where the input voltage is low (typically 12V) and large voltage boost (4 to 5) are desired. The first part of this thesis suggests multi-phase boost converter to overcome the disadvantages of large size storage capacitor in boost converter. Comparison between the specification of single stage and multi-stages is thoroughly examined. Besides the average small signal analysis of N converters in parallel and obtaining an equivalent second order system are discussed. By paralleling the converters the design of closed loop control is a demanding task. To achieve proper current sharing among the stages using current control method is inevitable. Design and implementation of closed loop control of multi-phase boost converter both in analog and digital is the topic of next part of the thesis. Comparison between these two approaches is presented in this part and it will be shown that digital control is more convenient for such a topology on account of the requirement of synchronization, phase shifted operation, current balancing and other desired functions, which will be discussed later in detail. A new direct digital control method, which is simple and fast, is developed. Two different realizations with DSP controller and FPGA controller are considered. In the last part of the thesis a novel soft switching circuit for boost converter is presented. It provides Zero Voltage Switching (ZVS) for the main switch and Zero Current Switching (ZCS) for the auxiliary switch. The paper presents the idealized analysis giving all the circuit intervals and the equations necessary for the design of such a circuit. The proposed soft switching circuit is particularly suited for the tapped-inductor boost circuit with a minimum number of extra components. Extension of the method to tapped inductor boost converter addresses the application of Zero Voltage Transition (ZVT) to high conversion ratio converters. Extension of the method to multiphase boost converter shows that with less number of auxiliary switches soft switching operation can be achieved for all interleaved switching devices. Several laboratory prototype boost converters have been built to confirm the theoretical results and design methods are matching with both simulation and experimental results.

Η μόλυνση του περιβάλλοντος από τα μέσα μεταφοράς και η συνεχής μείωση των αποθεμάτων των ορυκτών καυσίμων αποτελούν τους δύο κύριους λόγους για τη στροφή των τμημάτων έρευνας της παγκόσμιας αυτοκινητοβιομηχανίας στην επινόηση οικολογικότερων μέσων μετακίνησης. Από αυτή την προσπάθεια προέκυψαν τα ηλεκτρικά υβριδικά οχήματα, τα οποία περιορίζουν την κατανάλωση καυσίμου και τις εκπομπες ρύπων συγκριτικά με συμβατικά οχήματα παραπλήσιων τεχνικών χαρακτηριστικών. Τα υβριδικά οχήματα είναι, ουσιαστικά, ο προάγγελος και το πεδίο δοκιμής και εξέλιξης της αμιγούς ηλεκτροκίνησης. Ο κοινός στόχος της παρούσας διπλωματικής εργασίας και άλλων δύο διπλωματικών εργασιών, οι οποίες εκπονήθηκαν παράλληλα με αυτή, είναι η μετατροπή ενός συμβατικού βενζινοκίνητου αυτοκινήτου σε ηλεκτρικό υβριδικό όχημα. Το αρχικό μέλημα υπήρξε η εύρεση του κατάλληλου οχήματος για τη συγκεκριμένη εφαρμογή. Την προμήθεια του οχήματος ακολούθησε η έρευνα της αγοράς για την εύρεση του κατάλληλου ηλεκτρικού κινητήρα. Ο κινητήρας, ο οποίος επιλέχθηκε, είναι τριφασικός ασύγχρονος. Εν συνεχεία, αγοράστηκαν συσσωρευτές οξέος μολύβδου ως εναλλακτική πηγή ενέργειας του οχήματος. Ακολούθησε εμπεριστατωμένη μελέτη για τη μηχανολογική προσαρμογή του ηλεκτρικού κινητήρα και των συσσωρευτών στο όχημα και πραγματοποιήθηκε αυτή η εργασία. O ηλεκτρικός κινητήρας τοποθετήθηκε επί του διαφορικού, ενώ κατασκευάστηκε ειδική βάση για τους συσσωρευτές. Υπολογίστηκε και κατασκευάστηκε κατάλληλο σύστημα μετάδοσης για τη μεταφορά της κίνησης από τον κινητήρα στον άξονα μετάδοσης της κίνησης του οχήματος, ώστε να ανταποκρίνεται στις ανάγκες κίνησης του. Το γεγονός ότι ο κινητήρας χρειάζεται σύστημα υδρόψυξης για την ασφαλή και αποδοτική λειτουργία του είχε ως αποτέλεσμα την κατασκευή κατάλληλης διάταξης. Το δεδομένο ότι οι συσσωρευτές παράγουν συνεχές ρεύμα, ενώ ο κινητήρας απαιτεί τροφοδοσία με εναλλασσόμενο ρεύμα οδήγησε στην κατασκευή ενός τριφασικού αντιστροφέα ισχύος. Ο αντιστροφέας αποτελεί μια ηλεκτρική διάταξη, η οποία μετατρέπει το συνεχές ρεύμα σε εναλλασσόμενο. Το απαιτούμενο επίπεδο τάσης εξόδου του αντιστροφέα για την τροφοδοσία του κινητήρα προϋποθέτει συγκεκριμένο επίπεδο τάσης στην είσοδο του μετατροπέα, το οποίο είναι υψηλότερο από την τάση εξόδου της συστοιχίας των συσσωρευτών. Επιχειρήθηκε, λοιπόν, η εξομοίωση και η κατασκευή ενός αμφικατευθυντήριου μετατροπέα συνεχούς τάσης σε συνεχή. Η ιδιότητα του είναι η ανύψωση του επιπέδου τάσης των συσσωρευτών κατά τη φάση της τροφοδότησης του κινητήρα αλλά και ο υποβιβασμός της τάσης για τη φόρτιση των συσσωρευτών κατά την επιστροφή ενέργειας από τη λειτουργία του κινητήρα ως γεννήτρια, τη λεγόμενη διαδικασία της αναγεννητικής πέδησης. Ο έλεγχος του ηλεκτρικού κινητήρα πραγματοποιήθηκε μέσω της τεχνικής του άμεσου ελέγχου ροπής (DTC), ενός είδους άμεσου διανυσματικού ελέγχου. / The environmental pollution caused by all means of transport and the continued reduction of stocks of fossil fuels are the two main reasons, which directed the global automotive research in developing “greener” means of transport. From this effort emerged hybrid electric vehicles, which reduce fuel consumption and emissions compared to conventional vehicles with similar technical characteristics. Hybrid vehicles are essentially the precursor and the field for testing and developing pure electric traction. The common objective of this and two other diploma theses, which were prepared in parallel with it, is to convert a conventional gasoline car to a hybrid electric one. The initial concern was to find a suitable vehicle for this application. The supply of the vehicle was followed by the market research to find a suitable motor. The selected motor is a three-phase asynchronous motor. Subsequently, lead acid batteries were purchased as an alternative energy source for the vehicle. This was followed by a thorough study of the mechanical adjustment of the electric motor and battery in the vehicle and the planned work was performed. The electric motor is adapted on the differential and a base was constructed to fit the batteries. A suitable transmission system was built to transmit motion from the electric motor to the transmission axle of the vehicle to meet the needs of the driving conditions. The fact that the motor needs a water cooling system for its safe and efficient operation resulted in the construction of an adequate array. Taking into account that the batteries produce direct current, while the motor requires the supply of alternating current led to the design and construction of a three-phase power inverter at the laboratory. The inverter is an electrical device that converts direct current to alternating current. The demanded level of voltage in the inverter’s output to power the motor requires a specific voltage level at the input of the converter, which is higher than the output voltage of the battery pack. Therefore, the simulation and the construction of a bidirectional DC to DC voltage converter was attempted at the laboratory. The aim is to raise the level of battery voltage during the phase of the electric machine functioning as a motor and to reduce the voltage level to charge the batteries during the phase that the electric machine functions as a generator, a process called regenerative braking. The control of the electric motor was achieved by the technique of direct torque control (DTC), a kind of direct vector control.

Η παρούσα διπλωματική εργασία πραγματεύεται τη μετατροπή ενός συμβατικού αυτοκινήτου σε υβριδικό ηλεκτρικό όχημα. Προς αυτή την κατεύθυνση, μελετάται και κατασκευάζεται το ηλεκτροκινητήριο σύστημα του οχήματος, το οποίο έχει τοπολογία παράλληλης διάταξης. Τα υποσυστήματα που το συνθέτουν είναι ένας τριφασικός ασύγχρονος ηλεκτρικός κινητήρας, μία συστοιχία ηλεκτροχημικών συσσωρευτών και οι απαραίτητοι ηλεκτρονικοί μετατροπείς ισχύος. Το υβριδικό όχημα διαθέτει τη δυνατότητα επιστροφής ενέργειας κατά την επιβράδυνση, φορτίζοντας τους ηλεκτροχημικούς συσσωρευτές (αναγεννητική πέδηση). Για την προσαρμογή του ηλεκτροκινητήριου συστήματος στο υπάρχον συμβατικό κινητήριο σύστημα του αυτοκινήτου έλαβαν χώρα ορισμένες μηχανολογικές μετατροπές και κατασκευάστηκε ένα σύστημα υδρόψυξης για τον ηλεκτροκινητήρα. Για τη ενεργειακή διαχείριση του όλου συστήματος έγινε εμπεριστατωμένη ηλεκτρολογική μελέτη. Για την τροφοδοσία του τριφασικού ασύγχρονου κινητήρα σχεδιάστηκε και κατασκευάστηκε ένας ηλεκτρονικός μετατροπέας ισχύος συνεχούς τάσης σε τριφασική εναλλασσόμενη τάση (τριφασικός αντιστροφέας). Για τη λειτουργία του τριφασικού κινητήρα σε επίπεδα ονομαστικής ισχύος απαιτήθηκε η ανύψωση της συνεχούς τάσης των μπαταριών και για αυτό το λόγο έγινε σχεδιασμός, προσομοίωση και κατασκευή ενός αμφικατευθυντήριου ηλεκτρονικού μετατροπέα ανύψωσης/υποβιβασμού συνεχούς τάσης σε συνεχή τάση. Ο έλεγχος της ηλεκτρικής μηχανής υλοποιείται από την μέθοδο Αμέσου Ελέγχου Ροπής (DTC), η οποία αποτελεί ένα είδος αμέσου διανυσματικού ελέγχου. Παράλληλα με αυτή τη διπλωματική εργασία, εκπονήθηκαν δύο ακόμα διπλωματικές εργασίες πάνω στο θέμα του υβριδικού οχήματος. / The present diploma thesis deals with the conversion of a conventional car to a hybrid electric vehicle (HEV). To this direction, the powertrain of the vehicle is designed and constructed, composing a parallel hybrid topology. The subsystems of the electric propulsion system are a three-phase asynchronous electric motor, an electrochemical battery pack and the necessary power electronic converters. The hybrid electric vehicle has the ability to return energy and charge the batteries during deceleration (regenerative braking). In order to adapt the electrical compounds to the existing conventional propulsion system, some mechanical modifications had to be made. Furthermore, a water cooling system was designed and constructed in order to cool the electric motor. The energy management of the electrical system is analysed. The power of the three-phase asynchronous motor is controlled by a three-phase DC to AC inverter. The operation of the motor at its nominal power requires the boost of the battery voltage level. For this reason, a bidirectional DC to DC boost / buck converter was firstly simulated to ensure its proper operation. The above power converters were designed and constructed at the laboratory. The control of the electric motor is implemented by the Direct Torque Control method (DTC), which is a kind of direct vector control. In parallel with this work, two more diploma theses were prepared on the project of the hybrid electric vehicle.

This dissertation discusses the interaction between fuel cells and the DC-DC converter just connected across its terminals. For that, it presents a modified algorithm to represent the dynamic behavior of fuel cell stacks as much the current ripple effects from power converters on such cells. PEM type fuel cells (Proton Exchange Membrane) are studied to get a reasonable model of the electrochemical and electric characteristics of the involved phenomena in the generation of electric energy from fuel cells. A T filter is used as interface between the fuel cell and the DC-DC converter. This converter must prevent large current ripples going through the cell terminals as well as keeping constant the power flow between the FC and the link DC to prevent itself of possible current transient. To connect it to the grid it was used a three-phase DC-AC converter to inject or to absorb current from the grid at reduced ripple distortion and to stabilize the DC link voltage. DC current controllers were designed to curb the link DC and AC currents within reasonable limits. Validation of the model was carried out through computer simulation in order to have an evaluation of the control system behavior both for the stack and for the injection and/or absorption of energy. Also, theoretical results with practical data from a fuel stack were compared with respect to the load variation across its terminals. / Esta dissertação discute a interação entre as células de combustível e o conversor de potência conectado aos seus terminais. Para isto é apresentado um algoritmo modificado para a modelagem dinâmica de conversores chaveados tanto quanto um estudo sobre os efeitos das ondulações de corrente sobre as células. Células do tipo PEM (Proton Exchange Membrane) são estudadas, obtendo-se um modelo razoável para análise das características eletroquímicas e elétricas dos fenômenos envolvidos na geração de energia elétrica com células de combustível. Como interface utiliza-se um conversor CC-CC associado a um filtro do tipo T . Este conversor tem a função de evitar a grande ondulação de corrente absorvida pela célula bem como, manter constante o fluxo de potência entre a FC e o barramento CC evitando-se assim, possíveis transitórios nos terminais da célula. O projeto do conversor de potência prevê a conexão à rede da concessionária através de um conversor CC-CA trifásico para injetar ou absorver corrente da rede com reduzida distorção harmônica e estabilização da tensão do barramento CC. Foram projetados controladores para a corrente CC, a tensão CC e a corrente CA. Como formas de validação foram realizadas simulações para avaliar o comportamento dos sistemas de controle para a pilha e para a injeção e/ou absorção de energia. Também foram comparados os resultados teóricos com os dados práticos de uma pilha submetida à variação de carga em seus terminais.

A utilização de conversores multiníveis tem sido uma importante alternativa para aplicações de alta potência e média tensão, graças aos altos níveis de potência alcançáveis por estas estruturas. Recentemente, esta topologia de conversores foi aplicada em sistemas com fontes alternativas para alimentar um sistema de geração distribuída, nos quais diferentes fontes de energia eram utilizadas. Com base nas características dos conversores multinível e sua potencial aplicabilidade em sistemas de geração distribuída, este trabalho tem como objetivo construir um sistema multinível conectado a rede de distribuição para utilização de fontes alternativas de energia como fontes primárias. Considerando que a energia fornecida pelas fontes alternativas pode sofrer variações, propõe-se a integração de sistemas armazenadores de energia, como capacitores, ao sistema multinível. Por isso, este trabalho desenvolve uma estratégia de controle para máxima transferência de potência ativa entregue à rede a fim de obter um fluxo ótimo. A topologia multinível deste trabalho possui em sua configuração dois módulos inversores conectados em série. Neste caso, é possível que pelo menos um desses inversores funcione com uma modulação em baixa frequência processando a maior parcela de potência. Assim, duas estratégias de controle modulação de fase e modulação de amplitude para a transferência de potência realizada pelo inversor de baixa frequência são analisadas. As vantagens e desvantagens de cada um dos métodos são expostas e então a estratégia mais adequada, no caso a modulação de amplitude, é utilizada na operação do conversor multinível. Além disso, são apresentados a modelagem das plantas e o projeto dos controladores de cada um dos módulos inversores. Por fim, a validação da proposta é feita através dos resultados de simulações e experimentais que mostram a capacidade do sistema de geração em transferir potência constante para a rede de distribuição e manter a corrente quase sem distorções em fase com a tensão. / The utilization of multilevel converters has been an important alternative for medium voltage applications with high power and power quality demand, thanks to the high power levels achievable for this kind of structure. Recently, this converter topology was proposed as a new possibility in renewable energy source applications, mainly in system delivering power to the grid, where different renewable energy resources may be used. Based on the characteristics of multilevel converters, and their potential applicability in distributed generation systems, this study aims to build a multilevel system that could be powered by renewable energy sources as primary sources and then connect them to a distribution grid. However, considering the energy produced by alternative sources can vary, it is analyzed the integration of a storage energy system in this multilevel topology. Taking into account this ends, the main concern of this study is related to the development of a control strategy to maximize the active power transferred to the grid. The multilevel topology employed in this study has two H-bridge inverter modules connected in series forming a cascaded configuration. Therefore, it is possible that at least one of these inverters, operating with a low frequency of modulation, process the majority of power with lower amount of losses. On this way, two control strategies for power transfer are analyzed. The advantages and disadvantages of each method are presented, and the most appropriated strategy is used in the operation of the multilevel converter system. In addition, it has been presented the design criteria for each controller and finally the validation of the proposed approach is done by mains of simulations and experimental results which show the ability of the converter to transfer constant active power to the grid and keep the grid current in phase with the grid voltage.