This thesis presents an investigation into the characteristics of and driving methods for light emitting diode (LED) lamp system. A comprehensive overview on the lighting development is proposed. The characteristic of the light emitting diode (LED) lamp is described and the requirements of the ballast for the light emitting diode (LED) lamp are presented. Although LED lamps have longer lifetime than fluorescent lamps, the short lifetime limitation of LED driver imposed by electrolytic capacitor has to be resolved. Therefore, an LED driver without electrolytic capacitor in the whole power conversion process is preferred. In this thesis, a single phase, power factor correction converter without electrolytic capacitors for LED lighting applications is proposed, which is a modified SEPIC converter working in discontinuous conduction mode (DCM). Different with a conventional SEPIC converter, the middle capacitor is replaced with a valley-fill circuit. The valley-fill circuit could reduce the voltage stress of output diode and middle capacitor under the same power factor condition, thus achieving higher efficiency. Instead of using an electrolytic capacitor for the filter, a polyester capacitor of better lifetime expectancy is used. An interleaved power factor correction SEPIC with valley fill circuit is proposed to further increase the efficiency and to reduce the input and output filter size and cost. The interleaved converter shows the features such as ripple cancellation, good thermal distribution and scalability. / Master of Science

Power factor correction (PFC) converter is a species of switching mode power supply (SMPS) which is widely used in offline frond-end converter for the distributed power systems to reduce the grid harmonic distortion. With the fast development of information technology and multi-media systems, high frequency PFC power supplies for servers, desktops, laptops and flat-panel TVs, etc. are required for more efficient power delivery within limited spaces. Therefore the critical conduction mode (CRM) PFC converter has been becoming more and more popular for these information technology applications due to its advantages in inherent zero-voltage soft switching (ZVS) and negligible diode reverse recovery. With the emerging of the high voltage GaN devices, the goal of achieving soft switching for high frequency PFC converters is the top priority and the trend of adopting the CRM PFC converter is becoming clearer. However, there is the stringent electromagnetic interference (EMI) regulation worldwide. For the CRM PFC converter, there are several challenges on meeting the EMI standards. First, for the CRM PFC converter, the switching frequency is variable during the half line cycle and has very wide range dependent on the AC line RMS voltage and the load, which makes it unlike the traditional constant-frequency PFC converter and therefore the knowledge and experience of the EMI characteristics for the traditional constant-frequency PFC converter cannot be directly applied to the CRM PFC converter. Second, for the CRM PFC converter, the switching frequency is also dependent on the inductance of the boost inductor. It means the EMI spectrum of the CRM PFC converter is tightly related the boost inductor selection during the design of the PFC power stage. Therefore, unlike the traditional constant-frequency PFC converter, the selection of the boost inductor is also part of the EMI filter design process and EMI filter optimization should begin at the same time when the power stage design starts. Third, since the EMI filter optimization needs to begin before the proto-type of the CRM PFC converter is completed, the traditional EMI-measurement based EMI filter design will become much more complex and time-consuming if it is applied to the CRM PFC converter. Therefore, a new methodology must be developed to evaluate the EMI performance of the CRM PFC converter, help to simplify the process of the EMI filter design and achieve the EMI filter optimization. To overcome these challenges, a novel mathematical analysis method for variable frequency PFC converter is thus proposed in this dissertation. Based on the mathematical analysis, the quasi-peak EMI noise, which is specifically required in most EMI regulation standards, is investigated and accurately predicted for the first time. A complete approximate model is derived to predict the quasi-peak DM EMI noise for the CRM PFC converter. Experiments are carried out to verify the validity of the prediction. Based on the DM EMI noise prediction, worst case analysis is carried out and the worst DM EMI noise case for all the input line and load conditions can be found to avoid the overdesign of the EMI filter. Based on the discovered worst case, criteria to ease the DM EMI filter design procedure of the CRM boost PFC are given for different boost inductor selection. Optimized design procedure of the EMI filter for the front-end converter is then discussed. Experiments are carried out to verify the validity of the whole methodology. / Ph. D.

Efficiency is a driving constraint for electrical power systems as global energy demands are ever increasing. Followed by the introduction of diesel generators, electricity has become available in more locations than ever. However, operating a diesel generator on its own is not the most energy efficient. This is because the high crest factor loads, of many applications, decrease the fuel efficiency of a hydrocarbon generator. To understand this, we need to understand how an electrical load affects a generator. Starting with a load profile, a system designer must choose a generator to meet peak demand, marking the first instance where a load profile has influence over a generator. This decision will insure that brownouts do not occur, but, this will lead to poor energy efficiency. We say this because a generator is most energy efficient under heavier loads, meaning, during lighter loads, more fuel will be consumed to produce the same amount of energy. While this may be fine if the peak load was close to the average load, however, the actual crest factor for a typical residential load profile is much higher. This gap between peak and average load means that a generator will spend most of its time operating at its most inefficient point. To compensate for this, and reduce fuel consumption, the Mechatronics Lab at Virginia Tech has developed a mobile hybrid power system (MHPS) to address this problem. The solution was to augment a diesel generator with a battery pack. This allowed us to constrain the generator so that it only operates with fixed efficiency. It is the theory behind this system that will be covered in this thesis. / Master of Science

Este trabalho apresenta o estudo de um carregador de baterias monofÃsico aplicado a veÃculos elÃtricos. Este carregador à composto por dois estÃgios de processamento de energia e um circuito digital de supervisÃo para controlar a tensÃo sobre o banco de baterias e a corrente de recarga das mesmas. O primeiro estÃgio consiste de um conversor CA-CC bridgeless com caracterÃstica de alto fator de potÃncia, e o segundo estÃgio à representado por um conversor CC-CC fullbridge com isolamento em alta frequÃncia e comutaÃÃo sob tensÃo nula (Zero Voltage Switching â ZVS). Para ambos os conversores, foi realizada uma anÃlise qualitativa e quantitativa, bem como apresentados exemplos de projeto para facilitar o dimensionamento dos componentes. Finalmente, com os componentes escolhidos, foi montado um protÃtipo que permite carregar de uma atà oito baterias de 12 V conectadas em sÃrie. O sistema apresenta como especificaÃÃes: tensÃo de entrada alternada de 220 VÂ15%; tensÃo de saÃda contÃnua de 120 V; corrente de saÃda contÃnua de 20 A; e potÃncia mÃdia de saÃda de 2,4 kW. / This work presents a single-phase battery charger for electric vehicles. This converter is composed by two energy processing stages and a digital circuit to control the voltage across the batteries and their respective charging current. The first stage is a high power factor ACDC bridgeless converter, while the second one consists on a ZVS (Zero Voltage Switching) high frequency isolated DC-DC full-bridge converter. For both converters, the qualitative and quantitative analyses have been performed, as well as design examples have been presented in order to ease the components calculation. Finally, a prototype that allows charging up to eight series-connected 12 V batteries has been built. The system specifications are: AC input voltage of 220 V Â15%; DC output voltage of 120 V; DC output current of 20 A; and average output power of 2.4 kW.

Ce travail vise une exploration et une évaluation de nouvelles variantes de topologies multiniveaux AC/DC non réversibles (PFC) du point de vue de leur sûreté de fonctionnement : recherche d'une grande sécurité électrique sur destruction interne et maintien d'une continuité de fonctionnement. Elles sont caractérisées par une connexion AC non différentielle, un partitionnement cellulaire en série et symétrique autour d'un point milieu. Cette organisation permet d'exploiter la redondance active série entre les cellules d'un même groupe et l'effet de ségrégation topologique qui apparaît entre les deux groupes de cellules. Les structures étudiées sont modulaires et peuvent être parallélisées et étendues à un nombre quelconque de phases. Elles ne possèdent que des cellules mono-transistors basse-tension (Si et SiC 600V max) performantes et intrinsèquement tolérantes aux imperfections de la commande et aux parasites donc naturellement sécurisées. Les comparaisons prenant en compte les pertes, la répartition des pertes, le dimensionnement et le report de contraintes sur défaut interne mettent en avant la structure PFC Double- Boost Flying Cap. à 5 Niveaux, brevetée en début de thèse, comme une solution ayant le meilleur compromis. Sur le plan théorique nous montrons que le seul calcul de la fiabilité basé uniquement sur un critère d'occurrence au premier défaut est inadapté pour décrire ce type de topologie. La prise en compte de la tolérance de panne est nécessaire et permet d'évaluer la fiabilité globalement sur une panne effective (i.e. au second défaut). L'adaptation de modèles théoriques de fiabilité à taux de défaillance constant mais prenant en compte, au niveau de leurs paramètres, le report de contrainte en tension et l'augmentation de température qui résulte d'un premier défaut, permet de chiffrer par intégration et en valeur relative, le gain obtenu sur un temps court. Ce résultat est compatible avec les systèmes embarqués et la maintenance conditionnelle. Un prototype monophasé à 5 niveaux, à commande entièrement numérique et à MLI optimisée reconfigurable en temps réel a été réalisé afin de valider l'étude. Il permet une adaptation automatique de la topologie de 5 à 4 puis à 3 niveaux par exemple. Ce prototype a également servi de banc de test d'endurance du mode de défaillance sur claquage - avalanche de transistors CoolMos™ et diodes SiC, volontairement détruits individuellement dans des conditions d'énergie maîtrisée et reproductibles, afin de prouver expérimentalement le maintien du service sur plusieurs centaines d'heures au prix d'un derating de 30% maximum en puissance seulement. La détection et le diagnostic rapide de défauts internes ont également été traités dans ce travail. D'une part, par la surveillance directe et le seuillage des tensions internes (tensions flottantes) et d'autre part, par une détection harmonique de la fréquence de base (amplitude et phase) en temps réel. Ces deux techniques ont été intégrées numériquement et évaluées sur le prototype, en particulier la seconde qui ne requiert qu'un seul capteur. VI Enfin, nous proposons dans ce travail une nouvelle variante PFC Vienna multicellulaire expérimentée en fin de mémoire, utilisant deux fois moins de transistors et de drivers pour les mêmes performances fréquentielles au prix d'un rendement et d'une répartition des pertes légèrement moins favorables que la structure brevetée.

In this work, single stage power factor corrected AC/DC converters for LEDs / single stage Flyback converter having different configuration from the traditional Flyback and single stage SEPIC converter is investigated. The study involves analysis, circuit design, performance comparisons and implementation. The study covers LEDs / their developments, characteristics and state-of-art in this new technology. The circuits are investigated by means of computer simulations. Operating principles and operating modes are studied along with design calculations. After applying prototypes in laboratory, the simulation results and theoretical analyses are confirmed. The single stage Flyback converter has high voltage input (220-240 Vac), and the output feeds up to 216 HB-LEDs, with the ratings of 24 V, 3.25 A with 90 W. The single stage SEPIC converter with universal input (80-265 Vac) has an output that feeds 21 power LEDs, with 67 V, 0.30 and 20 W ratings.

In this thesis an educational test bench for studying the power quality attributes of the commonly used single-phase full-bridge diode rectifiers with power factor correction (PFC) circuits is designed and tested. This thesis covers the active and passive power factor correction methods for single-phase bridge rectifier. Passive filtering approach with dc side inductor and tuned filter along with active filtering approach via singleswitch boost converter is considered. Analysis, simulation, and design of a single phase rectifier and PFC circuits is followed by hardware implementation and tests. In the active PFC approach, various control methods is applied and compared. The educational bench is aimed to useful for undergraduate and graduate power electronics course, power quality related laboratory studies.

Three novel single-stage electronic ballasts with the advantages of high-power-factor, low current harmonic, high efficiency, and low cost are proposed for rapid-start fluorescent lamps. Included are (1) single-stage high-power-factor electronic ballast with asymmetrical topology, (2) single-stage high- power-factor electronic ballast with symmetrical topology, and (3) single-stage single-switch high-power-factor electronic ballast. The circuit configurations are obtained by integrating the buck-boost power-factor-correction converter into the Class D or the Class E resonant inverter. With simple circuit configuration and less component count, desired circuit performances of high-power-factor and high efficiency are realized. The control methods of pulse-width-modulation (PWM) with asymmetrical and symmetrical approaches are utilized for the three presented ballasts. The buck-boost conversion stage is operated at discontinuous current mode (DCM) to achieve nearly unity power factor at a fixed switching frequency. With carefully designed circuit parameters, the power switches can exhibit either zero-voltage switching-on (ZVS) or zero-current switching-on (ZCS). As a result, high circuit efficiency can be ensured. Design equations are derived and computer analyses are performed based on the lamp¡¦s equivalent resistance model and fundamental approximation. Accordingly, design guidelines for determining circuit parameters are provided. Prototypes of the three proposed circuits designed for a T8-36W lamp, two series-connected T9-40W lamps and a PL-27W lamp are built and tested to verify the computer simulations and analytical predictions.

Η παρούσα διπλωματική εργασία πραγματεύεται την μελέτη και το σχεδιασμό μιας τριφασικής ανορθωτικής διάταξης με την οποία επιτυγχάνεται διόρθωση του συντελεστή ισχύος. Η εργασία αυτή εκπονήθηκε στο Εργαστήριο Ηλεκτρομηχανικής Μετατροπής Ενέργειας του Τμήματος Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών της Πολυτεχνικής Σχολής του Πανεπιστημίου Πατρών. Κύριος σκοπός αυτής της διπλωματικής εργασίας είναι η κατασκευή ενός μετατροπέα ανόρθωσης ανύψωσης ο οποίος λειτουργεί σε ασυνεχή αγωγή και μπορεί να τοποθετηθεί στην έξοδο μιας ανεμογεννήτριας σαν πρώτο στάδιο σύνδεσης με το δίκτυο. Απώτερος σκοπός είναι η πειραματική επιβεβαίωση της θεωρίας καθώς και του μηχανισμού με τον οποίο επιτυγχάνεται η διόρθωση του συντελεστή ισχύος. Αρχικά γίνεται μια γενική αναφορά στην έννοια της ποιότητας ισχύος, τα χαρακτηριστικά της μεγέθη, το συντελεστή ισχύος και τις ανώτερες αρμονικές. Επίσης αναφέρονται βασικές τριφασικές ανορθωτικές διατάξεις με διορθωμένο συντελεστή ισχύος ενώ γίνεται και μια γενική αναφορά στα αιολικά συστήματα, τον τρόπο λειτουργίας τους και την σύνδεση τους με το δίκτυο. Στη συνέχεια, αναλύεται η λειτουργία του μετατροπέα που κατασκευάστηκε κατά την διάρκεια αυτής της διπλωματικής εργασίας, δηλαδή τριφασικής διάταξης ανόρθωσης-ανύψωσης με ένα διακοπτικό στοιχείο, που λειτουργεί στην περιοχή ασυνεχούς αγωγής (DCM). Ο μετατροπέας αυτός θα δέχεται πολική τάση στην είσοδο του 40-100V, ανυψώνοντας την στα 350V στην έξοδο. Παράλληλα το ρεύμα εισόδου έχει μικρό αρμονικό περιεχόμενο επιτυγχάνοντας έναν υψηλό συντελεστή ισχύος. Το επόμενο βήμα είναι η μοντελοποίηση και η προσομοίωση του μετατροπέα σε περιβάλλον Matlab/Simulink έτσι ώστε να εξακριβωθεί η ορθή λειτουργία του σύμφωνα με τη θεωρητική ανάλυση. Τέλος, μελετάται και κατασκευάζεται στο εργαστήριο η πειραματική διάταξη με την οποία διεξάγονται μετρήσεις για την επιβεβαίωση και αξιολόγηση της θεωρητικής μελέτης. / In this diploma thesis the analysis and design of a three phase rectifier achieving high power factor are presented. This work was developed in the Laboratory of Electromechanical Energy Conversion at the Department of Electrical Engineering and Computer Technology of the Polytechnic School, University of Patras, Greece. The main purpose of this diploma thesis is the implementation of a Power Factor Correction Three Phase Rectifier operated in Discontinuous Current Mode (DCM) which can be used as a first stage for the connection of a small wind turbine to the grid. Through this work, the theoretical analysis and the mechanism that achieves the high power factor are verified through the implementation of a laboratory prototype. Initially, the concepts of power quality, power factor and high order harmonics are explained. Furthermore, some common power factor correction rectifier topologies are reported as well as a reference on wind turbines, their operation and their connection to the grid. Secondly, the working principle of the Single Switch Power Factor Correction DCM Boost Rectifier is presented. This converter is designed to rectify and boost the voltage of a small wind turbine, varying between 40 and 100V line to line rms, to 350Vdc. In addition the converter’s input current presents low harmonic distortion which results in a high power factor. The following step is to model and simulate the converter in Matlab/Simulink in order to verify its operation based on the theoretical analysis. Finally, a laboratory prototype is designed and implemented, on which experiments are conducted, in order to verify and evaluate the theoretical study.

In this thesis, a new approach for single-stage power factor correction converters is proposed to increase their power ratings to be in the multiple kilowatts levels. The proposed techniques are based on the utilization of modified three-level resonant converter topologies. These topologies provide low component stresses, high frequency operation, zero voltage switching, applicability under a wide range of input and output conditions as well as added control flexibility. The proposed control algorithms are based on a combination of variable frequency and asymmetrical pulse width modulation control or variable frequency and phase shift modulation control. In either case, the variable frequency control is used to tightly regulate the output voltage, whereas, pulse width or phase shift modulation is used to regulate the dc-bus voltage as well as the input power factor. New converter topologies, their operation and steady state and dynamic analyses are presented in details. A modelling approach based on average multiple frequency methods is also proposed. This approach leads to the development of a full order state space model with the two control variables explicitly separated allowing a better controller design. The model can be used either at high level of detail expressing the non-linearities of the system or it can readily be simplified to a linear decoupled model for approximate solutions. Finally, a discrete time controller for the proposed converters, which is suitable for FPGA implementation, is presented. Analytical, simulation and experimental results are provided to verify the proposed concepts. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2008-01-30 14:28:15.725