While high power buck-boost regulators have been extensively researched and developed in the academia and industry, low power counterparts have only recently gained momentum due to the advent of different battery powered and remote electronics. The application life-time of such applications, e.g., remote surveillance electronics can be extended tremendously by enabling energy autonomy. While battery powered electronics last long but they must be replenished once the battery is depleted either by replacing the battery or by retrieving the electronics and then recharging. Instead, energy harvesting from available ambient sources on the spot will enable these electronics continuous operation unboundedly, probably even beyond the lifetime of the electronics. Interestingly enough, recent advancements in micro-scale energy transducers compliment these demand [1-13]. Micro-transducers producing energy from different ambient sources have been reported. These transducers produce enough energy to support a wide range of operations of the remote electronics concurrently. These transducers along with an additional storage elements greatly increase the energy autonomy as well as guaranteed operation since harvested energy can then be stored for future use when harvestable energy is temporarily unavailable. Recently several buck-boost regulators with low power and low input operating voltage have been reported both from academia and industry [14-24]. Some of this work focuses on increasing efficiency in the mid-load range (10mA-100mA), while some other focuses on lowering input range. However, so far no one has reported a buck-boost regulator operating with sub-200nW bias power while harvesting energy from sub-500mV input range. This work focuses on the development of a low voltage low bias current buckboost regulator to attain these goals. In this work, complete design of a PFM mode buck-boost regulator has been discussed in details. Basic topology of the regulator and working principle of the implemented architecture along with the advantages of the specific topology over that of the others have been discussed in short to provide an uninterrupted flow of idea. Later, Transistor level design of the basic building blocks of the buck-boost regulator is discussed in details with different design features and how those are attained through transistor level implementation are discussed. Subsequently, the physical layout design technique and considerations are discussed to inform the reader about the importance of the layout process and to avoid pitfalls of design failure due to layout quality issues. Measurement results are presented with the fabricated IC. Different characterization profile of the IC have been discussed with measured data and capture oscilloscope waveforms. Load regulation, line regulation, efficiency, start-up from low voltage, regulation with line and load transient events are measured, presented and discussed. Different characteristics of the prototype are compared with prior arts and are presented in a comparison table. Die micrograph is also presented along with the different issue of the IC testing

Streptococcus mutans is the main causative agent of dental caries, which is a widespread infectious disease. A number of surface molecules are involved in the pathogenicity of this organism, including adherence and aggregation factors. The wall-associated protein A (WapA) of Streptococcus mutans GS-5 was previously demonstrated to be a sucrose-dependent adherence and aggregation factor, and is a larger precursor to extracellular antigen A (AgA), a candidate antigen for a dental caries vaccine.The full-length wapA gene and a C-terminal truncated version agA encoding the AgA were cloned into the mammalian expression vector pcDNA 3.1/V5/His-TOPO. The above constructs were mixed with a cationic lipid and used to transfect Chinese hamster ovary (CHO) cells. Transient expression of the wapA and agA genes was observed at 24 h post-transfection, as shown by Western immunoblot analysis. In CHO, cells WapA containing the membrane and wall-spanning region was found in apoptotic bodies, whereas the soluble AgA, which lacked the hydrophobic region, was found in extracellular medium. A higher salivary IgA level was observed in mice immunized with the pcDNA-wapA vaccine as compared to those immunized with the pcDNA-agA vaccine. Furthermore, the anti-WapA antibody inhibited S. mutans sucrose-dependent adherence, suggesting potential protection of the tooth against S. mutans colonization, while anti-AgA had no significant effect. Indeed, prediction and analysis of protein epitopes showed that WapA contains highly promiscuous MHC-II binding motifs that are absent from AgA. Immunodot assay confirmed that WapA bound biotin-labeled dextran, whereas AgA did not.

The demand for power converters is on the rise due to their ability to achieve high power conversion efficiency, small size, light weight and reduced cost. DC-DC converters are used in many applications where, the output voltage needs to be regulated for wide variations in the input voltage and the load. They are also used in applications where electrical isolation is required. Power generation from renewable energy sources suffers from highly fluctuating output voltages. Electrical isolation of renewable energy sources from the grid is essential. Therefore, DC-DC converters are used as an integral part of the power electronic interface required for grid integration of renewable energy sources such as wave energy power conversion. In this dissertation as a first step, the power converters used in wave energy applications are classified and compared. Analysis, design, simulation and experimental results of fixed frequency controlled HF transformer isolated DC-DC resonant converters are presented. The first converter topology presented in Chapter 3 is a ‘fixed frequency controlled single-phase high frequency (HF) transformer isolated DC-DC LCL-type series resonant converter (SRC) with capacitive output filter using a modified gating scheme’. Working of this converter has been explained. Modeling and steady-state analysis of the converter using approximate complex ac circuit analysis method has been done. Various design curves have been obtained. A step-by-step design procedure has been illustrated with an example of a 200 W converter. PSIM simulation results for different operating conditions are presented. Experimental model of the designed converter has been built and the test results are given. Power loss breakdown analysis of the converter has been made. Zero-voltage switching (ZVS) is achieved for different input voltages, and load. This converter cell can be used in interleaved operation to realize higher power converters. The second topology presented in Chapter 4 is ‘a fixed-frequency controlled, 3-phase HF transformer isolated, integrated boost dual 3-phase bridge DC-DC LCL-type SRC with capacitive output filter’. Detailed modeling of the boost section and one of the two identical 3-phase inverter modules is presented. Analysis of the inverter module using approximate complex ac circuit analysis method is presented. Various design curves have been obtained. A step-by-step design procedure has been illustrated with an example of a 600 W converter. Detailed PSIM simulation results for different operating conditions are presented. Experimental model of the designed converter has been built and the test results are given. Power loss breakdown analysis has been made. Major advantage of this converter has been its ability to regulate the output voltage for wide variations in the input voltage and load, while maintaining ZVS for all the switches. Also, due to the parallel connection of the inverter modules the component stresses are significantly reduced. This encourages the converter to be used in high power applications such as wave energy. A 10 kW DC-DC converter cell of the second topology mentioned above has been designed to illustrate the design and working of a high power converter. Performance of the designed converter has been verified by PSIM simulations. This converter operates with ZVS for all the switches for a wide variation in the input voltage and the loading conditions. Power loss breakdown analysis has been performed. / Graduate

Η παρούσα διπλωματική εργασία πραγματεύεται τη μελέτη και κατασκευή ενός μετατροπέα συνεχούς τάσης σε εναλλασσόμενη (αντιστροφέας) που προορίζεται για τη σύνδεση ενός φωτοβολταϊκού πλαισίου στο δίκτυο χαμηλής τάσης. Η εργασία εκπονήθηκε στο Εργαστήριο Ηλεκτρομηχανικής Μετατροπής Ενέργειας του Τμήματος Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών του Πανεπιστημίου Πατρών. Αρχικά, παρουσιάζονται, συνοπτικά, πληροφορίες για τη φωτοβολταϊκή τεχνολογία και για τους τρόπους διασύνδεσής τους με την κατανάλωση ή το δίκτυο. Στη συνέχεια, γίνεται αναφορά στον αντιστροφέα της διπλωματικής εργασίας. Πιο συγκεκριμένα, μελετάται ένας διαφορικός αντιστροφέας τύπου boost, ένα χαρακτηρισμό που τον οφείλει στην δυνατότητα, να επιτευχθεί μέσω αυτού εναλλασσόμενη τάση εξόδου με ενεργό τιμή μεγαλύτερη της συνεχούς τάσης εισόδου. Ο μετατροπέας αυτός αποτελείται στην ουσία από δύο επιμέρους μετατροπείς dc-dc τύπου boost, με τη συνδυασμένη λειτουργία των οποίων επιτυγχάνεται η επιθυμητή μετατροπή. Η ονομαστική ισχύς για την οποία πραγματοποιείται ο σχεδιασμός του μετατροπέα είναι ίση με 250W. Με δεδομένα τα μεγέθη ρευμάτων και τάσεων, καθώς και των κυματώσεων στα ρεύματα των πηνίων και στις τάσεις των πυκνωτών, υπολογίστηκαν οι τιμές των στοιχείων, βάσει των οποίων έγιναν οι προσομοιώσεις. Κατόπιν, δοκιμάστηκαν σε προσομοίωση διάφορες μορφές ελέγχου του αντιστροφέα, με μόνη ικανοποιητική αυτή του έλεγχου με ολίσθηση στο πεδίο καταστάσεων. Αυτός ήταν και ο έλεγχος που τελικά επιλέχθηκε για τη διάταξη που μελετήθηκε, γι’ αυτό και γίνεται αναλυτική περιγραφή του ελέγχου αυτού. Λόγω των απαιτήσεών του αποφασίστηκε ο έλεγχος να υλοποιηθεί χωρίς χρήση μικροελεγκτή, αλλά με χρήση αποκλειστικά ολοκληρωμένων αναλογικών κυκλωμάτων. Ακολουθεί η περιγραφή της διαδικασίας σχεδίασης και κατασκευής του μετατροπέα που έγινε στο Εργαστήριο Ηλεκτρομηχανικής Μετατροπής Ενέργειας και παρουσιάζονται τα επιμέρους στοιχεία και οι συνδεσμολογίες που χρησιμοποιήθηκαν. Τέλος, περιγράφονται τα πειράματα που πραγματοποιήθηκαν και παρατίθενται τα αποτελέσματα που προέκυψαν, αποδεικνύοντας την ορθή λειτουργία της διάταξης. Επίσης, εξάγονται τα ανάλογα συμπεράσματα. / In this diploma thesis, a Power Inverter in order to connect an Alternating Current-Photovoltaic (AC-PV module) to the low voltage grid is analyzed, designed and manufactured. The work was carried out in the Laboratory of Electrical and Mechanical Energy Conversion at the Department of Electrical and Computer Engineering of the Polytechnic School, University of Patras, Greece. At first, some data and information concerning the photovoltaic technology are presented as well as the connection modes of a PV system or module. Secondly, the operation and structure of the inverter is described. Specifically, a differential output boost inverter is examined, the title of which is derived from its ability to produce an output voltage larger than the input voltage. In fact, this converter consists of two boost dc-dc converters, the combined operation of which achieves the desirable operation of the inverter. The nominal power of the inverter is chosen to be equal to 250W. Depending on the expected values of the currents and voltages, as well as on the ripple voltages of the capacitors and the ripple currents of the inductors, the component values were calculated. The following step was to simulate the operation of the converter under different control techniques. The only control method with satisfying results which was eventually applied to the inverter was the sliding mode control, so it is extensively described. Due to its requirements, this control technique was implemented without using a microcontroller, but only using analog integrated circuits. The design and implementation of the inverter is then described along with the selected components and some individual circuits. Finally, the results of the conducted experiments are presented, the good operation of the setup is confirmed and the related conclusions are derived.

This thesis aims to develop proposals and models for a modular electronics construction to a future D250S Dual battery charger. The aim also includes investigation of possibilities to use some of Texas Instruments C2000 microprocessors. The reason for this is that CTEK SWEDEN AB wants to renew the present D250S Dual battery charger and lower the manufacturing costs. The thesis work has involved gathering theoretical facts for the development of a design on the modular electronic construction, the choice on which microprocessor to use, the choice of electronic components and facts about peripheral equipment to the D250S Dual. With the theoretical there has been developed different solutions to the proposed hardware and software solutions with comparisons in aspects of positive and negative. The thesis work is only a feasibility study to a future D250S Dual. The development of a future D250S Dual needs more work to make it possible to do a proof of concept.

A single-phase, buck-boost based, dual-output AC-DC converter is studied in this thesis. The converter has two DC outputs with opposite polarities, which share the same ground with the input power line. The power stage performance, including the input filter, is studied and procedure to select power components is given. The circuit model is analyzed to develop appropriate control. Zerocrossing distortion of the source input current is addressed and a solution is proposed. Experimental results are satisfactory in that a high power factor line current results for steady-state operation.

Η παρούσα διπλωματική εργασία έχει ως αντικείμενο μελέτης την ανάπτυξη ενός μοντέλου κυψέλης καυσίμου (Fuel Cell), το οποίο θα αποτελέσει το βασικό στοιχείο της διεσπαρμένης παραγωγής ενέργειας από ένα σταθμό με τέτοιες κυψέλες που θα τροφοδοτεί ένα μικροδίκτυο. Η μελέτη θα περιλαμβάνει όλα εκείνα τα στοιχεία που είναι απαραίτητα για τη σύνδεση σε ένα δίκτυο. Συγκεκριμένα, θα περιλαμβάνει τον ανυψωτή τάσης (boost converter) ο οποίος είναι υπεύθυνος για την ανύψωση της συνεχούς τάσης εξόδου της στοίβας κυψελών καυσίμου, τον αντιστροφέα (inverter) ο οποίος θα μετατρέπει την συνεχή τάση εξόδου του ανυψωτή σε εναλλασσόμενη με το επιθυμητό πλάτος και συχνότητα, και τέλος θα περιλαμβάνει το σύστημα ελέγχου το οποίο θα προσπαθεί να ικανοποιεί τις ενεργειακές ανάγκες κάθε φορτίου ρυθμίζοντας κατάλληλα τις παραμέτρους των προηγούμενων μερών. / The currnet diploma thesis deal with the development of a PEM fuel cell, which will be the basic component of a distributed power system connected to a microgrid. This study will contain all the necessary components for a connection to the main grid. There will be boost converter to boost the output voltage of the fuel cell stack, an inverter to convert the dc voltage to ac-voltage with specific voltage amplitude and frequency. Moreover, there will be a control system which will be able to fulfill all the power requirements of the loads, regulating the parameters of the previous components.

Η παρούσα διπλωματική εργασία πραγματεύεται τη μελέτη και κατασκευή ενός ηλεκτρονικού μετατροπέα ισχύος ανύψωσης συνεχούς τάσης σε συνεχή. Η εργασία εκπονήθηκε στο Εργαστήριο Ηλεκτρομηχανικής Μετατροπής Ενέργειας του Τμήματος Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών της Πολυτεχνικής Σχολής του Πανεπιστημίου Πατρών. Σκοπός της εργασίας αυτής είναι η μελέτη και η κατασκευή ενός ηλεκτρονικού μετατροπέα ισχύος, ο οποίος θα αποτελέσει μέρος ενός ηλεκτροκινητήριου συστήματος με πηγή ενέργειας μία συσκευή κυψελών καυσίμου (fuel cells). Συγκεκριμένα πρόκειται για ένα μετατροπέα ανύψωσης συνεχούς τάσης σε συνεχή, με διαδοχική αγωγή δύο παράλληλων κλάδων (2-channel interleaved boost converter). Η είσοδος του μετατροπέα συνδέεται στην πηγή των κυψελών καυσίμου με σκοπό να ανυψώσει τη συνεχή αλλά μεταβλητή τάση που παράγει αυτή και να τη σταθεροποιήσει στα 50V. Στην έξοδο αυτού του μετατροπέα πρόκειται να συνδεθεί ένας αντιστροφέας για την οδήγηση τριφασικού σύγχρονου κινητήρα με μόνιμους μαγνήτες (BLDC), ο οποίος αποτελεί αντικείμενο άλλης διπλωματικής εργασίας, που εκπονείται στο Εργαστήριο. Για την επίτευξη αυτού του σκοπού χρειάστηκε θεωρητική μελέτη των διακοπτικών τροφοδοτικών συνεχούς τάσης αλλά και της πηγής κυψελών καυσίμου. Στη μελέτη βοήθησε το πρόγραμμα εξομοίωσης, με το οποίο εξομοιώθηκαν εκτός από το προαναφερθέν τελικό σύστημα και διάφορα άλλα συστήματα που αποτέλεσαν ιδέες για τη συγκεκριμένη εφαρμογή. Έπειτα ακολούθησε η κατασκευή της διάταξης και η διεξαγωγή πλήθους πειραματικών δοκιμών. / This diploma thesis deals with the study, design and construction of a power electronic boost converter. The work was conducted at the Laboratory of Electromechanical Energy Conversion of the Department of Electrical and Computer Engineering of School of Engineering of University of Patras. The main purpose of this work is the analysis and construction of a power electronic converter that will be part of an electric propulsion system which has a fuel cell stack as an electrical power source. Particularly, this power electronic converter is a two channel interleaved boost converter. This converter is connected to the fuel cells in order to boost and stabilize the unregulated voltage which they produce. At the output of this converter it will be connected an electronic power inverter which will drive a brushless DC motor (BLDC). For the accomplishment of this purpose, the study of both switching power supplies and fuel cells was needed. At this analysis the system was designed at a simulation program which gave useful information about the system operation. After the system simulation the converter was constructed and the entire system was set up in order to carry out the required experiments and measurements.

Η παρούσα διπλωματική εργασία ασχολείται με τη μελέτη και την κατασκευή μιας νέας τοπολογίας για τη διασύνδεση ενός φωτοβολταϊκού πλαισίου με το δίκτυο χαμηλής τάσης. Η διάταξη που επιλέχτηκε αποτελεί το πρώτο στάδιο ενός μετατροπέα δύο βαθμίδων που χρησιμοποιείται για την αντιστροφή της τάσης του φωτοβολταϊκού πλαισίου και τη σύνδεση αυτού με το δίκτυο. Η βασική λειτουργία της διάταξης είναι η ανύψωση και σταθεροποίηση της τάσης εισόδου στα επίπεδα των 400 V. Η επιλογή της τοπολογίας στηρίχτηκε στον απλό σχεδιασμό, το υψηλό κέρδος τάσης και την ύπαρξη ενός μόνο διακοπτικού στοιχείου. Το κύκλωμα που μελετήθηκε είναι ένας μετατροπέας Boost σε συνδυασμό με ένα μετατροπέα Flyback με δυο δευτερεύοντα τυλίγματα. Πιο συγκεκριμένα, το πηνίο του μετατροπέα Boost αντικαθίσταται από το πρωτεύον τύλιγμα του Μ/Σ Flyback, ενώ τα δύο δευτερεύοντα μεταφέρουν τη μαγνητική ενέργεια στην έξοδο με σκοπό την επιπλέον ενίσχυση της τάσης εξόδου που προσφέρει ο Boost. Η κατασκευή του μετατροπέα και του κυκλώματος ελέγχου πραγματοποιήθηκε στο Εργαστήριο Ηλεκτρομηχανικής Μετατροπής Ενέργειας. Τα πειραματικά αποτελέσματα επιβεβαίωσαν τη θεωρητική ανάλυση που έγινε και την ορθή λειτουργία του κυκλώματός μας. Ο μετατροπέας επιτυγχάνει υψηλά κέρδη τάσης (μέχρι και 20 φορές), ενώ ο βαθμός απόδοσης κρίνεται αρκετά ικανοποιητικός για επίπεδα ισχύος μέχρι 150 W, αφού μετρήθηκε πάνω από 85%. Ως προέκταση της κατασκευής, θα μπορούσε να υλοποιηθεί βρόχος ανάδρασης με σκοπό τη σταθεροποίηση της τάσης εξόδου στα 400 V καθώς και M.P.P.T. έλεγχος για τη βέλτιστης λειτουργίας της Φ/Β γεννήτριας εισόδου. / --

Albuquerque, L. T. Retificador ativo com alto fator de potência utilizando controle indireto de corrente por deslocamento de amostra de tensão. 2017. 148 f. Dissertação (Mestrado em Engenharia Elétrica e de Computação) - Campus de Sobral, Universidade Federal do Ceará, Sobral, 2017. / Submitted by Programa de Pós-Graduação Engenharia Elétrica e de Computação (secretaria_ppgeec@sobral.ufc.br) on 2017-10-18T15:51:33Z No. of bitstreams: 1 2017_dis_ltalbuquerque.pdf: 3310839 bytes, checksum: 6d6c80a5608fbfe18bb9b3b3579d5e38 (MD5) / Approved for entry into archive by Djeanne Costa (djeannecosta@gmail.com) on 2017-10-19T13:56:08Z (GMT) No. of bitstreams: 1 2017_dis_ltalbuquerque.pdf: 3310839 bytes, checksum: 6d6c80a5608fbfe18bb9b3b3579d5e38 (MD5) / Made available in DSpace on 2017-10-19T13:56:08Z (GMT). No. of bitstreams: 1 2017_dis_ltalbuquerque.pdf: 3310839 bytes, checksum: 6d6c80a5608fbfe18bb9b3b3579d5e38 (MD5) Previous issue date: 2017 / This master thesis presents a power factor correction technique for single phase current sensorless Boost Bridgeless rectifier, digitally implemented. The technique is based on input voltage samples, used as modulating signal to generate the PWM pulses. The control of power flow is made by shifting the modulating signal, i.e. the input sampled voltage. The advantages of this technique are: the absence of the current control loop; no need of current sensor; use of processors with low computational capability; the Phase Locked Loop is not needed; efficiency for any input voltage waveform. In order to validate the proposed technique, simulations were performed and collected experimental results from a 500W rated power prototype, by which power factors were obtained around 0.996, and harmonic distortion within the limits of IEC 61000-3-2:2014. / Este trabalho apresenta uma técnica para correção de fator de potência com um retificador Boost Bridgeless monofásico sem utilização de sensor de corrente, implementada digitalmente. Esta técnica utiliza amostras da tensão de entrada deslocadas no tempo como sinal modulador, as quais são utilizadas para o acionamento dos interruptores do retificador. A técnica proposta se diferencia das demais pelo fato de não necessitar de uma malha de controle da corrente de entrada, de não utilizar sensor de corrente, de possibilitar a utilização de processadores com reduzida capacidade computacional, de não necessitar da utilização de Phase Locked Loop (PLL) e por poder ser aplicada a quaisquer formas de onda periódica da tensão de entrada. A fim de validar a técnica proposta foram realizadas simulações e coletados resultados experimentais a partir de um protótipo de 500W de potência, com o qual foram obtidos fatores de potência da ordem de 0,996, além de taxas de distorção harmônica dentro dos limites da Norma IEC 61000-3-2:2014.