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.

Driven by the limitations of solar-optimized roof space and International Energy Association (IEA) Task 35, there is a renewed interest in photovoltaic solar thermal (PVT) hybrid systems. Current PVT systems focus on cooling the solar photovoltaic (PV) cells to improve the electrical performance. This however, causes the thermal component (T) to underperform. An exergetic study was completed comparing a PVT, PV + T and a PV only system in Detroit, Denver and Phoenix. It was found that the PVT system outperformed the PV + T system by 72% for each location and by 8, 8.6 and 9.9% for Detroit, Denver and Phoenix when compared to the PV only system. To further improve the PVT system, using hydrogenated amorphous silicon (a-Si:H) PV as the absorber layer of the solar thermal device was explored. The temperature coefficient and annealing properties of a-Si:H allow the thermal component to run more efficiently, while enabling the a-Si:H i-layers to be thicker resulting in more electricity production. It was found that running i-layer thicker cells (630nm and 840nm) stabilized at higher efficiencies at 90°C (potential PVT operating temperatures) than the thinner cell (420nm) by 2% and 0.5% respectively. In addition, spike annealing, which is a new concept of stagnating a PVT system to allow for the a-Si:H PV to anneal and return it to its original efficiencies was also investigated. It was found that over the lifetime of the system with the spike annealing occurring once a day 10.6% more electricity was produced than a system without stagnation. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2011-11-14 11:09:16.727

This thesis presents a novel Zero Voltage Switching (ZVS) approach in a grid connected single-stage flyback inverter without using any additional auxiliary circuits. The soft-switching of the primary switch is achieved by allowing negative current from the grid-side through bidirectional switches placed on the secondary side of the transformer. Basically, the negative current discharges the MOSFET’s output capacitor thereby allowing turn-on of the primary switch under zero voltage. In order to optimize the amount of reactive current required to achieve ZVS a variable frequency control scheme is implemented over the line cycle. In addition, the bi-directional switches on the secondary side of the transformer have ZVS during the turn-on times. Therefore, the switching losses of the bi-directional switches are negligible. A 250W prototype has been implemented in order to validate the proposed scheme. Experimental results confirm the feasibility and superior performance of the converter compared to the conventional flyback inverter. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2012-07-06 16:24:13.385

Cette thèse concerne le couplage des systèmes photovoltaïques (PV) au réseau de distribution du point de vue contrôle/commande et rejet de perturbation. Le raccordement au réseau induit des couplages aux effets parfois indésirables. Le problème majeur est dû aux creux de tension provoqué par des court-circuits, à la foudre ou encore à certaines manœuvres. Dans ce contexte, des déconnexions apparaissent et parfois sont non-jutifiées, tout particulièrement en cas de défaut sur un départ adjacent BT/HTA; en cas d'un fort taux de pénétration de systèmes PV, une telle déconnexion qui serait généralisée peut avoir des conséquences néfastes. Les travaux de cette thèse se sont focalisés sur ce problème de couplage : effet des systèmes PV sur le réseau et réaction des systèmes PV face aux perturbations du réseau. A cet effet, des adaptations aux protections découplage sont proposées pour une intégration harmonieuse du système PV. Des stratégies de gestion de l'énergie ont été également mises au point participation à l'amélioration de la qualité de l'énergie localement et pour la tenue des systèmes PV aux perturbations.

Black rot caused by Xanthomonas campestris pv. campestris (X. c pv. campestris) is a major disease constraint to cabbage production. The control of black rot is difficult and resistant cultivars could play an important role in reducing the losses due to the disease. Information on the distribution and diversity of X. c pv. campestris is critical before any meaningful disease resistance screening can be done. However, little is known about the diversity and international significance of South African X. c pv. campestris strains. To assess the genetic diversity and international significance of X. c pv. campestris strains in South Africa, strains of the pathogen were obtained from cabbage growing districts in Gauteng, Mpumalanga and North West Provinces of South Africa in 2010. International strains were obtained from international culture collections. Isolates from South Africa were purified and race typed using differential sets of Brassica spp according to Nickerson–Zwaan protocols. Four races, race 1(14%), race 3 (7%), race 4 (68%) and race 6 (10%) of the pathogen were identified. Repetitive DNA polymerase chain reaction–based fingerprinting using Eric– and Box–primers were used to assess the genetic diversity. Polyacrylamide gel electrophoresis allowed clear and reproducible differentiation of the PCR products. Of the amplified loci for South African isolates 5 loci were present in at least 90 % of the isolates for Eric–profiles and 6 in at least 80% of the isolates for Box–profiles. Of these prominent loci, none had corresponding high presence in international isolates. While no loci had a presence greater than 51% and 61% for Eric– and Box– profiles in international isolates, respectively, several loci among South African isolates were unique to isolates from specific geographic origin. Generated fingerprints of X. c pv. campestris were similar for the South African isolates and distinguishable from those of X. c pv. armoraciae and X. c pv. raphani reference strains. However, when international X. c pv. campestris were considered, no profile pattern was observed to be unique to international X. c pv. campestris isolates as was the case with South African isolates. Eric– and Box–PCR profiles of international isolates varied widely with some isolates having profile patterns similar to those of reference strains. Cluster analysis divided X. c pv. campestris into two major groups, the South African group and the international isolates group. The South African group could be divided into subgroups, which clustered according to the geographical origin of the isolates. The same was observed for international isolates, which generally clustered isolates according to country of origin. However, isolates from different countries also clustered together. A few X. c pv. campestris strains of international origin clustered with the South African isolates group. Furthermore, a few South African isolates were clustered in the international isolate group. Although X. c pv. campestris distribution may be unique to its geographical origin, our findings, based on the present data set, suggest wide spread of the pathogen both at national and international level. The existence of different races, genetic variability and international distribution of the pathogen should be considered when resistant crucifer cultivars are bred to control black rot of crucifers / Thesis (M.Sc. (Microbiology))--North-West University, Potchefstroom Campus, 2011.

Black rot caused by Xanthomonas campestris pv. campestris (X. c pv. campestris) is a major disease constraint to cabbage production. The control of black rot is difficult and resistant cultivars could play an important role in reducing the losses due to the disease. Information on the distribution and diversity of X. c pv. campestris is critical before any meaningful disease resistance screening can be done. However, little is known about the diversity and international significance of South African X. c pv. campestris strains. To assess the genetic diversity and international significance of X. c pv. campestris strains in South Africa, strains of the pathogen were obtained from cabbage growing districts in Gauteng, Mpumalanga and North West Provinces of South Africa in 2010. International strains were obtained from international culture collections. Isolates from South Africa were purified and race typed using differential sets of Brassica spp according to Nickerson–Zwaan protocols. Four races, race 1(14%), race 3 (7%), race 4 (68%) and race 6 (10%) of the pathogen were identified. Repetitive DNA polymerase chain reaction–based fingerprinting using Eric– and Box–primers were used to assess the genetic diversity. Polyacrylamide gel electrophoresis allowed clear and reproducible differentiation of the PCR products. Of the amplified loci for South African isolates 5 loci were present in at least 90 % of the isolates for Eric–profiles and 6 in at least 80% of the isolates for Box–profiles. Of these prominent loci, none had corresponding high presence in international isolates. While no loci had a presence greater than 51% and 61% for Eric– and Box– profiles in international isolates, respectively, several loci among South African isolates were unique to isolates from specific geographic origin. Generated fingerprints of X. c pv. campestris were similar for the South African isolates and distinguishable from those of X. c pv. armoraciae and X. c pv. raphani reference strains. However, when international X. c pv. campestris were considered, no profile pattern was observed to be unique to international X. c pv. campestris isolates as was the case with South African isolates. Eric– and Box–PCR profiles of international isolates varied widely with some isolates having profile patterns similar to those of reference strains. Cluster analysis divided X. c pv. campestris into two major groups, the South African group and the international isolates group. The South African group could be divided into subgroups, which clustered according to the geographical origin of the isolates. The same was observed for international isolates, which generally clustered isolates according to country of origin. However, isolates from different countries also clustered together. A few X. c pv. campestris strains of international origin clustered with the South African isolates group. Furthermore, a few South African isolates were clustered in the international isolate group. Although X. c pv. campestris distribution may be unique to its geographical origin, our findings, based on the present data set, suggest wide spread of the pathogen both at national and international level. The existence of different races, genetic variability and international distribution of the pathogen should be considered when resistant crucifer cultivars are bred to control black rot of crucifers / Thesis (M.Sc. (Microbiology))--North-West University, Potchefstroom Campus, 2011.

Pseudomonas syringae pv. syringae B728a, an aggressive bacterial pathogen of bean, utilizes large surface populations and extracellular signaling to initiate a fundamental change from an epiphytic to a pathogenic lifestyle. Extracytoplasmic function (ECF) sigma (σ) factors serve as important regulatory factors in responding to various environmental signals. Bioinformatic analysis of the B728a genome has revealed 10 ECF sigma factors, five of which have high levels of sequence similarity to the FecI-type of ECF sigma factors and play a known role in the regulation of various iron transport systems. Because iron is essential for the induction of major virulence factors in B728a, I hypothesized that these FecI-type sigma factors may play a critical role in the bacterium’s transition between lifestyles. Deletion mutants of two FecI-type sigma factors, Psyr_1040 and Psyr_1107, in B728a have been created using homologous recombination based on the phage λ Red recombinase method. This study shows that the B728a FecI-type sigma factors, Psyr_1040 and Psyr_1107 are affected by conditions of iron stress, and influence the expression of putative outer membrane receptors and transmembrane sensors associated with these genes. Moreover, Psyr_1107 contributes to the expression of a cluster of predicted pili assembly genes downstream of it. Mutations in Psyr_1040 and Psyr_1107 affect the population levels of B728a in bean plants, since in planta growth of deletion mutants of B728a lacking Psyr_1040 and Psyr_1107 appears to be slower than wild-type B728a. In this thesis, the possible roles of Psyr_1040 and Psyr_1107 in the adaptation of B728a to a pathogenic lifestyle are addressed using a combination of phenotypic characterization and quantitative real-time PCR (qRT-PCR) analyses.

京都大学 / 新制・課程博士 / 博士(エネルギー科学) / 甲第23997号 / エネ博第433号 / 新制||エネ||82(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー社会・環境科学専攻 / (主査)教授 石原 慶一, 教授 白井 康之, 准教授 尾形 清一 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

East Timor is rebuilding its stock of infrastructure after decades of underdevelopment and a wave of violent destruction in 1999. As part of this process the Government of East Timor aims to improve access to electricity from less than five percent of the population today to eighty percent by 2020. An important strategy to meeting this aim will be the use of solar home systems (SHS) in remote rural locations. To develop its policy for the deployment of SHS, the Government of East Timor must decide what size of SHS is optimal. This research investigates whether there is a relationship between SHS size and development. / The research adapts an evaluation approach developed by World Bank/UNDP Energy Sector Management Assistance Program. This approach uses a combination of participatory and quantitative tools tailored to the East Timorese context through consultations with rural households about electrification and their use of SHS. Three SHS projects in East Timor were selected for evaluation, each of which had adopted a different sized SHS for their program. The smallest systems installed were 10 Wp single-lamp systems. The largest system was rated at 80 Wp and was supplied with four or six lamps. The third type of system was 40 Wp and provided three lamps / To assess the development impact of these different sizes of SHS, a set of Participatory Evaluation exercises were conducted with seventy-seven small groups of SHS users in twenty four rural communities. These exercises were supplemented with a Socio-economic Household Survey of 195 SHS users. The combined results of these evaluation processes enabled the three sizes of SHS to be compared for two types of benefits—assistance with carrying out important household tasks (i.e. ‘lighting-derived’ benefits) and attributes of SHS which were advantageous in comparison to use of non-electric lighting sources (i.e. ‘intrinsic’ benefits). Analysis of the research results showed that the small 10 Wp SHS provided much of the development impact of the larger systems. For lighting-derived benefits, there was little difference between the development impact of small and large systems. The larger systems provided greater benefit for domestic tasks undertaken in kitchen buildings, since the small and medium sized SHS did not provide lighting in these areas. For intrinsic benefits related to health and convenience, the small systems provided much the same benefits as larger systems. For financial benefits—considered by East Timorese SHS users to be the most important of the intrinsic benefits—smaller systems were found to offer slightly positive benefits due to their lower operating costs. Larger systems, however, were found to have a negative overall financial impact. / The research suggests three significant implications for the design of SHS programs in East Timor and comparable situations elsewhere: programs should focus on providing smaller systems rather than larger ones; systems should be designed to provide a light in the kitchen wherever possible to maximise the overall development impact; and SHS operating costs should be carefully matched to the incomes of rural householders to ensure that operation of the systems can be sustained by user households.

East Timor is rebuilding its stock of infrastructure after decades of underdevelopment and a wave of violent destruction in 1999. As part of this process the Government of East Timor aims to improve access to electricity from less than five percent of the population today to eighty percent by 2020. An important strategy to meeting this aim will be the use of solar home systems (SHS) in remote rural locations. To develop its policy for the deployment of SHS, the Government of East Timor must decide what size of SHS is optimal. This research investigates whether there is a relationship between SHS size and development. / The research adapts an evaluation approach developed by World Bank/UNDP Energy Sector Management Assistance Program. This approach uses a combination of participatory and quantitative tools tailored to the East Timorese context through consultations with rural households about electrification and their use of SHS. Three SHS projects in East Timor were selected for evaluation, each of which had adopted a different sized SHS for their program. The smallest systems installed were 10 Wp single-lamp systems. The largest system was rated at 80 Wp and was supplied with four or six lamps. The third type of system was 40 Wp and provided three lamps / To assess the development impact of these different sizes of SHS, a set of Participatory Evaluation exercises were conducted with seventy-seven small groups of SHS users in twenty four rural communities. These exercises were supplemented with a Socio-economic Household Survey of 195 SHS users. The combined results of these evaluation processes enabled the three sizes of SHS to be compared for two types of benefits—assistance with carrying out important household tasks (i.e. ‘lighting-derived’ benefits) and attributes of SHS which were advantageous in comparison to use of non-electric lighting sources (i.e. ‘intrinsic’ benefits). Analysis of the research results showed that the small 10 Wp SHS provided much of the development impact of the larger systems. For lighting-derived benefits, there was little difference between the development impact of small and large systems. The larger systems provided greater benefit for domestic tasks undertaken in kitchen buildings, since the small and medium sized SHS did not provide lighting in these areas. For intrinsic benefits related to health and convenience, the small systems provided much the same benefits as larger systems. For financial benefits—considered by East Timorese SHS users to be the most important of the intrinsic benefits—smaller systems were found to offer slightly positive benefits due to their lower operating costs. Larger systems, however, were found to have a negative overall financial impact. / The research suggests three significant implications for the design of SHS programs in East Timor and comparable situations elsewhere: programs should focus on providing smaller systems rather than larger ones; systems should be designed to provide a light in the kitchen wherever possible to maximise the overall development impact; and SHS operating costs should be carefully matched to the incomes of rural householders to ensure that operation of the systems can be sustained by user households.