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.

AC/DC adapters mostly employ two-stage topology: Power Factor Correction (PFC) pre-regulation stage followed by an isolated DC/DC converter stage. Low power AC/DC adapters require a small size to be competitive. Among their components, the bulk DC-link capacitor is one of the largest because it should keep the output voltage with low ripple. Also, the size of this capacitor is penalized due to the universal line voltage application. Synchronization through employing leading edge modulation for the first PFC stage and trailing edge modulation for the second DC/DC converter stage can significantly reduce the ripple current and ripple voltage of the DC-link capacitor. Thus, a smaller DC-link capacitance can be used, lowering the cost and size of the AC/DC adapter. Benefits of the synchronous switching scheme were already demonstrated experimentally. However, no mathematical analysis was presented. In this thesis, detailed mathematical analyses in per-unit quantity are given to facilitate the calculation of the DC-link capacitor ripple current reduction with Leading/Trailing Edge Modulation strategies. One of the limitations of leading/trailing edge modulation is that the switching frequencies of the two stages need to be equal to achieve the best reduction of the DC-link capacitor ripple current. The DC-link capacitor ripple current will become larger if the switching frequency of the DC/DC converter is larger than that of the PFC pre-regulator, which blocks us to employ higher frequency for isolated DC/DC converter to reduce its transformer size. This thesis proposed a new Leading/Trailing Edge Modulation strategy to further reduce the DC-link bulk capacitor ripple current when switching frequency of DC/DC converter stage is twice the switching frequency of PFC stage. This proposed pulse width modulation scheme was verified by simulation. Experimental results obtained through digital control based on FPGA are also presented in this thesis.

The research presents two novel high power factor ac-to-dc resonant converters with symmetrical topologies and zero-voltage-switching (ZVS) operation. The derived circuits are obtained from the integration of a dual-switch boost-type or buck-boost-type power factor corrector (PFC) into a half-bridge resonant converter. With symmetrical topology, the circuit is simple and the voltage and current stresses on the two active power switches are identical to each other. The PFC is operated at discontinuous conduction mode (DCM) to achieve unity power factor. The resonant energy tank of half-bridge resonant converter is designed to be inductive to retain ZVS operation. The design equations are derived based on fundamental approximation. Prototypes of the two proposed converters designed for 100 W and 50 W, respectively, were built and tested to verify the computer simulations and analytical predictions. Satisfactory results are obtained experimentally.

The on-going interest in thermoelectric (TE) materials, in the form of bulk and films, motivates investigation of materials that exhibit low thermal conductivity and good electrical conductivity. Such materials are phonon-glass electron-crystals (PGEC), and the multi-component type-I clathrate Ba8Ga16Ge30 is in this category. This work reports the first investigation of Ba8Ga16Ge30 films grown by pulsed laser deposition (PLD). This dissertation details the in-situ growth of polycrystalline type-I clathrate Ba8Ga16Ge30 thin-films by pulsed laser ablation. Films deposited using conventional laser ablation produced films that contained a high density of particulates and exhibited weak crystallinity. In order to produce high quality, polycrystalline, particulate-free films, a dual-laser ablation process was used that combines the pulses of (UV) KrF excimer and (IR) CO2 lasers that are temporally synchronized and spatially overlapped on the target surface. The effect of the laser energy on stoichiometric removal of material and morphology of the target has been investigated. In addition, in-situ time-gated emission spectroscopy and imaging techniques were used to monitor expansion of components in the ablated plumes. Through these investigations, the growth parameters were optimized not only to significantly reduce the particulate density but also to produce large area stoichiometric films. Structure and electrical transport properties of the resultant films were also evaluated. This work provides new insight toward the in-situ growth of complex multi-component structures in thin-film form for potential TE applications.

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

In this thesis an analytical design method of the improved broadband passive harmonic filter (IBF) for three phase diode rectifier front-end type adjustable speed drives is presented. The method is based on frequency domain modeling of the rectifier and filter. The success of the method involves accurate representation of the load harmonics. With the harmonics well defined, the harmonic and fundamental frequency equivalent circuits are utilized to analytically calculate the voltages/currents. Thus, the size and the performance of the filter can be optimized. The analytical method is verified via computer simulations and laboratory experiments. Also a performance comparison of various passive harmonic filters for three-phase diode rectifier front-end type adjustable speed drives is provided. The comparison involves the input current total harmonic distortion, input power factor, rectifier voltage regulation, energy efficiency, size, and cost. The parallel/series harmonic resonance problem related issues are addressed and unbalanced operation performance investigated. The comparison is based on analysis and computer simulations and the results are validated by laboratory experiments.

The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on October 6, 2009). Thesis advisor: Dr. Naz E. Islam. Includes bibliographical references.

Η ραγδαία ανάπτυξη των ηλεκτρονικών ισχύος τα τελευταία χρόνια και η χρήση τους σε μια ποικιλία βιομηχανικών εφαρμογών οδήγησε στο πρόβλημα των ανώτερων αρμονικών. Η ύπαρξη ανώτερων αρμονικών επιφέρει πολλά προβλήματα στα συστήματα ηλεκτρικής ενέργειας και στα στοιχεία που τα αποτελούν. Για το λόγο αυτό, τοποθετούνται παθητικά φίλτρα που σκοπό έχουν να μειώσουν έως και να εξαλείψουν τις συνέπειες των αρμονικών. Ο σχεδιασμός των παθητικών αρμονικών φίλτρων μπορεί να γίνει με βάση διάφορα κριτήρια. Στην παρούσα διπλωματική εργασία, γίνεται σχεδιασμός παθητικών αρμονικών φίλτρων με τη βοήθεια των γενετικών αλγορίθμων που σκοπό έχουν τη μεγιστοποίηση του συντελεστή ισχύος. Η μεγιστοποίηση του συντελεστή ισχύος γίνεται αυξάνοντας την ωφέλιμη ισχύ (την ισχύ της θεμελιώδους αρμονικής), μειώνοντας τη μιγαδική ισχύ και εξαλείφοντας την ισχύ των ανώτερων αρμονικών (απώλειες). Πιο συγκεκριμένα: Στο 1ο κεφάλαιο γίνεται μια εισαγωγή στο πρόβλημα των ανώτερων αρμονικών καθώς και στις επιπτώσεις τους σε διάφορα τμήματα του εξοπλισμού ενός συστήματος ηλεκτρικής ενέργειας. Επίσης αναφέρεται συνοπτικά ο σκοπός των αρμονικών φίλτρων και της διπλωματικής εργασίας. Στο 2ο κεφάλαιο γίνεται εκτενής αναφορά στα παθητικά αρμονικά φίλτρα και σε θέματα που σχετίζονται με τα είδη, το μέγεθος, το κόστος, το σχεδιασμό και την προστασία των φίλτρων. Επιπλέον γίνεται μνεία στα όρια των αρμονικών βάσει του προτύπου 519-1992 του ΙΕΕΕ. Το 3ο κεφάλαιο γράφτηκε με σκοπό να αποτελέσει ένα εγχειρίδιο γενετικών αλγορίθμων. Ξεκινά με την ιστορική αναδρομή και γενικές έννοιες και επεκτείνεται σε ένα ευρύ φάσμα εφαρμογών. Επιπλέον γίνεται επεξήγηση των δυνατοτήτων του GA toolbox του Matlab καθώς και τα βήματα που θα πρέπει να ακολουθήσει κάποιος προκειμένου να χρησιμοποιήσει τους γενετικούς αλγορίθμους ως εργαλείο βελτιστοποίησης. 2 Στο 4ο κεφάλαιο γίνεται αναλυτική περιγραφή του συστήματος και των δεδομένων του, αποδεικνύεται το μαθηματικό μοντέλο που χρησιμοποιήσαμε και γίνεται αναφορά στα μεγέθη που θα υπολογιστούν. Επιπροσθέτως, παρουσιάζονται τα αποτελέσματα που προέκυψαν από τους γενετικούς αλγορίθμους για την περίπτωση των αρμονικών πηγής τάσης και για αυτή των αρμονικών πηγής ρεύματος έτσι ώστε να μεγιστοποιείται ο συντελεστής ισχύος. Τέλος, στο 5ο κεφάλαιο εξάγονται χρήσιμα συμπεράσματα τα οποία απορρέουν από το σχεδιασμό των παθητικών αρμονικών φίλτρων με τη χρήση των γενετικών αλγορίθμων έτσι ώστε να μεγιστοποιείται ο συντελεστής ισχύος. Εν κατακλείδι, αναφέρονται κάποιες μελλοντικές σκέψεις σχετικά με το σχεδιασμό παθητικών αρμονικών φίλτρων. / The rapid development of power electronics in recent years and their use in a variety of industrial applications led to the problem of higher harmonics. The existence of higher harmonics causes many problems in power electric systems and the elements they consist of. This is the reason why passive filters which are designed in order to reduce or even eliminate the effects of higher harmonics are used. The design of passive filters is based on various criteria. This Thesis, examines the design of passive harmonic filters (using genetic algorithms), which aim to maximize power factor. By increasing the useful power (power of fundamental harmonic), decreasing the apparent power and eliminating the power of higher harmonics (losses), the power factor is being maximized. More specific: The first chapter is an introduction to the problem of higher harmonics, as well as to their effects on various parts of electric power system equipment. There is also a summary of the purpose of harmonic filters and this thesis. In the second chapter extensive references are made on passive harmonic filters and issues relating to species, size, cost, design and protection of filters. In addition, reference is made to harmonic bounds, based on IEEE Standard 519-1992. The third chapter is written in order to serve as a handbook of genetic algorithms. It enters with the historical background of genetic algorithms and extends to their use on a wide range of applications. The potentials of Genetic Algorithm (GA) toolbox of Matlab are explained. The steps to be followed in order to use genetic algorithms as optimization tool are also mentioned. A detailed description of the system and its data is given in the fourth chapter. The mathematical model and its relations used to simulate our system are proved. An extensive reference is made to the units sizes that will be calculated. Additionally, the results obtained from the genetic algorithms both in the case of the harmonic voltage source and the harmonic current source, in order to maximize the power factor, are presented. Finally, in the fifth chapter, useful conclusions are drawn from the design of passive harmonic filters (using genetic algorithms). In addition some thoughts about alternative designs of passive harmonic filters are stated in this chapter.

Este trabalho apresenta uma nova topologia de conversor CA-CC trifásico de estágio único com elevado fator de potência baseado no conversor SEPIC MCD, contendo interruptores bidirecionais. Este se comporta como um seguidor da tensão mesmo em malha aberta (característica dos conversores SEPIC MCD), ou seja, emula uma resistência do ponto de vista da rede elétrica. Sendo assim, o esforço de controle é reduzido a apenas uma malha de controle, sendo esta para controlar a tensão de saída, como em um conversor CC-CC. Este conversor de estágio único tem elevada confiabilidade, uma vez que emprega quatro interruptores ativos, com o mesmo sinal de comando, e seis diodos de alta frequência para a conversão de corrente alternada para corrente contínua (CA-CC) com alto fator de potência e isolação em alta frequência. Como desvantagens, tem-se a restrição na escolha da relação de transformação, a qual implica em elevados valores de corrente no secundário para baixas tensões de saída. São apresentadas as etapas de operação, as formas de onda ideais, as equações que regem o funcionamento do conversor, os resultados de simulação numérica contrastados com os valores teóricos e resultados experimentais. As especificações aplicadas ao conversor são 127 V na tensão de entrada, 200 V na tensão de saída, 50 kHz da frequência de comutação e 1500 W de potência para a carga. O protótipo gerado a partir dessas especificações apresenta 0,9981 de fator de potência, 4,234% de taxa de distorção harmônica e um rendimento de 85,522% para condições nominais. Devido as suas características, considera-se uma boa opção para sistemas trifásicos de baixa potência, onde não se justifica um elevado custo. / This work presents a new three-phase high power factor single-stage AC-DC converter based on the DCM SEPIC topology, using bidirectional switches. This converter operates as a voltage follower even in open loop (SEPIC DCM converter characteristic), in other words, it emulates a resistance from the electric grid point of view. Therefore, the control effort is reduced to a single control loop to control the DC output voltage, like an output voltage control of a DC-DC converter. This single-stage converter has high reliability, since it employs four active switches with the same command signal and six high frequency diodes for AC-DC conversion with high power factor and high frequency isolation. A system disadvantage is related to the constraint in the choice of transformer turns, which leads to high current values in the secondary-side for lower output voltage specifications. Hereon are presented the operation modes, the ideal waveforms, the main equations of the converter, the numerical simulation results contrasting with the theoretical values and experimental results. Design specifications are 127 V input voltage, 200 V output voltage, 50 kHz switching frequency and 1500 W output power. The prototype is obtained by following the specifications and it shows 0.9981 of power factor, 4.234% of total harmonic distortion and 85.522% of efficiency for rated condition. This converter is considered a choice for low power three-phase systems with low cost realization.