Thesis (Ph. D.)--University of Hong Kong, 2007. / Also available in print.

The grid connected PV plants comprising of the PV cells and the power electronic inverters are a widely used technology in distributed power generation systems based on renewable energy sources. Microinverters form an extensive part of the ongoing research in this field. This thesis focuses on the inverter section of the microinverter. The cost and efficiency of the grid connected inverter is a chief contributing factor in the overall system price. The MOSFETs used in the DC/AC inverter are usually hard switched causing a lot of EMI noise and losses in the inverter. This is true for both, single and three phase inverters. A low switching frequency is desirable to increase the efficiency, which in turn imposes a large compromise in designing the output filter. In this thesis, switching losses have been minimized by incorporating zero voltage switching at switch turn on and variable dead-time control at switch turn off. The soft switching technique is based on control algorithms and involves no use of any auxiliary circuit. Also, the size of the output filter is reduced without increasing the switching frequency, by employing multiple paralleled inverters. The interleaving technique that is usually used in dc/dc converters is extended for dc/ac inverters and is well employed to maintain the quality of the current fed into the utility grid. In this way, at low switching frequency, high efficiency and reduced cost and sizes are achieved. The study is validated through simulation and lab experiments. The novel control circuit was first implemented using analog circuitry. After assessing the performance of the analog version of the proposed controller, it was then digitally implemented through the Field Programmable Gate Array (FPGA) technique. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2012-04-30 15:06:26.071

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Η διπλωματική εργασία ασχολείται με την προσομοίωση και την ενεργειακή μελέτη ενός αυτόνομου οικιακού φωτοβολταϊκού συστήματος ονομαστικής ισχύος 1,8 KW στον νομό Χίου. Αναφέρονται τα ηλεκτρικά στοιχεία που απαρτίζουν ένα τέτοιο σύστημα και η λειτουργία τους. Τέλος εκτελείται οικονομική ανάλυση του παραπάνω συστήματος και γίνεται η συγκρισή του με συμβατικό σύστημα. / The project studies the simulation and the energy behaviour of a stand alone photovoltaic system with rated power of 1,8 ΚW. There is an economic analysis of this system as well.

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

published_or_final_version / Architecture / Doctoral / Doctor of Philosophy

Este trabalho apresenta o desenvolvimento de uma metodologia para a etiquetagem e qualificação de inversores para Sistemas Fotovoltaicos Conectados à Rede, com finalidade de servir de proposta de procedimento para inclusão no Regulamento de Avaliação de Conformidade de Equipamentos e Sistemas Fotovoltaicos do Programa Brasileiro de Etiquetagem. O procedimento desenvolvido avalia os inversores quanto à eficiência, qualidade de energia, proteções e informações operacionais e de instalação. / This work presents the development of a methodology for qualification and labeling of inverters for grid-connected photovoltaic systems, aiming serving as procedural proposal for inclusion in the Conformity Assessment Rules of Equipments and Photovoltaic Systems of the Brazilian Labeling Program. The developed procedure evaluates the inverters efficiency, power quality, protections and operational and installation information.

Este trabalho apresenta o desenvolvimento de uma metodologia para a etiquetagem e qualificação de inversores para Sistemas Fotovoltaicos Conectados à Rede, com finalidade de servir de proposta de procedimento para inclusão no Regulamento de Avaliação de Conformidade de Equipamentos e Sistemas Fotovoltaicos do Programa Brasileiro de Etiquetagem. O procedimento desenvolvido avalia os inversores quanto à eficiência, qualidade de energia, proteções e informações operacionais e de instalação. / This work presents the development of a methodology for qualification and labeling of inverters for grid-connected photovoltaic systems, aiming serving as procedural proposal for inclusion in the Conformity Assessment Rules of Equipments and Photovoltaic Systems of the Brazilian Labeling Program. The developed procedure evaluates the inverters efficiency, power quality, protections and operational and installation information.

Solar energy is the energy derived from the sun through the form of solar radiation. Solar powered electrical generation relies on photovoltaic (PV) systems and heat engines. These two technologies are widely used today to provide power to either standalone loads or for connection to the power system grid. Maximum power point tracking (MPPT) is an essential part of a PV system. This is needed in order to extract maximum power output from a PV array under varying atmospheric conditions to maximize the return on initial investments. As such, many MPPT methods have been developed and implemented including perturb and observe (P&O), incremental conductance (IC) and Neural Network (NN) based algorithms. Judging between these techniques is based on their speed of locating the maximum power point (MPP) of a PV array under given atmospheric conditions, besides the cost and complexity of implementing them. The P&O and IC algorithms have a low implementation complexity but their tracking speed is sluggish. NN based techniques are faster than P&O and IC. However, they may not provide the global optimal point since they are prone to multiple local minima. To overcome the demerits of the aforementioned methods, support vector regression (SVR) based strategies have been proposed for the estimation of solar irradiation (for MPPT). A significant advantage of SVR based strategies is that it can provide the global optimal point, unlike NN based methods. In the published literature of SVR based MPPT algorithms, however, researchers have assumed a constant temperature. The assumption is not plausible in practice as the temperature can vary significantly during the day. The temperature variation, in turn, can remarkably affect the effectiveness of the MPPT process; the inclusion of temperature measurements in the process will add to the cost and complexity of the overall PV system, and it will also reduce the reliability of the system. The main goal of this thesis is to present a novel sensorless SVR based multi-stage algorithm (MSA) for MPPT in PV systems. The proposed algorithm avoids outdoor irradiation and temperature sensors. The proposed MSA consists of three stages: The first stage estimates the initial values of irradiation and temperature; the second stage instantaneously estimates the irradiation with the assumption that the temperature is constant over one-hour time intervals; the third stage updates the estimated value of the temperature once every one hour. After estimating the irradiation and temperature, the voltage corresponding to the MPP is estimated, as well. Then, the reference PV voltage is given to the power electronics interface. The proposed strategy is robust to rapid changes in solar irradiation and load, and it is also insensitive to ambient temperature variations. Simulations studies in PSCAD/EMTDC and Matlab demonstrate the effectiveness of the proposed technique.

Τα τελευταία χρόνια, υπό την πίεση της ολοένα αυξανόμενης επιβάρυνσης του περιβάλλοντος από την χρήση ορυκτών καυσίμων και υπό τον φόβο των μεγάλων κλιματικών αλλαγών των οποίων ήδη γινόμαστε μάρτυρες, έχει γίνει πολύς λόγος για την χρήση οικολογικών και περιβαλλοντικά φιλικών ενεργειακών λύσεων. Έτσι, έχουν χυθεί τόνοι μελανιού και έχουν ξοδευθεί δισεκατομμύρια χρηματικές μονάδες στις έρευνες για την εύρεση νέων μορφών ανανεώσιμης ενέργειας και βελτιστοποίηση της απόδοσης των ήδη υπαρχόντων. Μία λοιπόν ευρέως διαδεδομένη ανανεώσιμη μορφή ενέργειας, η οποία έχει βρει πεδίο ανάπτυξης και στην χώρα μας (υπό τον φόβο δυστυχώς των προστίμων της Ευρωπαϊκής Ένωσης και όχι από την ανάπτυξη εγγενούς περιβαλλοντικής συνείδησης), είναι η τεχνολογία των φωτοβολταϊκών (ΦΒ). Πρόκειται για μία αρκετά γνωστή στους επιστήμονες και τις ερευνητικές ομάδες ανανεώσιμη πηγή ενέργειας, των οποίων οι προσπάθειες έχουν μειώσει το κόστος των ΦΒ σε τέτοια επίπεδα, ώστε να κρίνεται οικονομικά συμφέρουσα μία επένδυση σε αυτά, ακόμα και για κατόχους μικρών κεφαλαίων. Η μορφή της ενέργειας όμως που παράγεται από μία ΦΒ συστοιχία δεν είναι άμεσα εκμεταλλεύσιμη, καθώς η συνεχής τάση που αυτά παράγουν δεν είναι κατάλληλη ούτε για μεταφορά από το δημόσιο δίκτυο ηλεκτρισμού, ούτε για κατανάλωση από τα φορτία, τα οποία λειτουργούν υπό εναλλασσόμενη τάση. Επομένως, μία συστοιχία για να είναι κατάλληλη προς σύνδεση στο δίκτυο, πρέπει να συνοδεύεται από κατάλληλες διατάξεις, η οποίες επιτρέπουν την μετατροπή της ενέργειας σε κατάλληλη μορφή, αλλά και τον βέλτιστο έλεγχό της. Σκοπός λοιπόν της παρούσας εργασίας είναι η αναφορά στις κύριες δομές λειτουργίας και ελέγχου ΦΒ διασυνδεδεμένων στο δίκτυο, καθώς η περίπτωση αυτή είναι η πιο πολύπλοκη, λόγω της δυναμικής που εισάγει μία σύνδεση με το δίκτυο μεταφοράς. Η δε δομή της διαμορφώνεται ως ακολούθως: 1o Κεφάλαιο: Δομές Ηλεκτρονικών Ισχύος για την Διασύνδεση στο Δίκτυο ΦΒ Συστημάτων Γίνεται μία γενική αναφορά στις υπάρχουσες τεχνολογίες αντιστροφέων και επιχειρείται μία γενική ομαδοποίηση τους 2ο Κεφάλαιο: Ανασκόπηση μονοφασικών διασυνδεδεμένων αντιστροφέων για ΦΒ πλαίσια Παρουσιάζονται γενικές τοπολογίες μονοφασικών αντιστροφέων, ταξινομούνται και συγκρίνονται ως προς διάφορα χαρακτηριστικά. 3ο Κεφάλαιο: Σύγκριση τεχνικών ανίχνευσης μεγίστου σημείου λειτουργίας ΦΒ συστοιχίας Είναι άκρως απαραίτητη η λειτουργία των πλαισίων στο σημείο λειτουργίας που εγγυάται την μέγιστη παραγωγή ισχύος, έτσι ώστε να κρίνεται συμφέρουσα μία επένδυση σε αυτά. Εδώ λοιπόν εξετάζονται αρκετές τέτοιες τεχνικές που υπάρχουν διαθέσιμες. 4ο Κεφάλαιο: Διακυμάνσεις τάσης που εισάγονται σε επίπεδο διανομής από ΦΒ συστήματα Τα ΦΒ στοιχεία μετατρέπουν την ηλιακή ενέργεια σε ηλεκτρική. Επομένως, είναι άμεσα εξαρτώμενη η παραγωγή τους από τις καιρικές συνθήκες. Στο παρόν κεφάλαιο παρουσιάζονται μέθοδοι πρόβλεψης τέτοιων διακυμάνσεων στην ηλιακή ενέργεια, και άρα στην παραγόμενη τάση. 5ο Κεφάλαιο: Συστήματα αποθήκευσης Κάθε σύστημα παραγωγής ηλεκτρικής ενέργειας, για να θεωρείται ολοκληρωμένο, θα πρέπει να μπορεί να αποθηκεύει την περίσσεια ενέργειας που μπορεί να παρουσιάσει σε κάποιες χρονικές περιόδους, και να την αποδώσει όταν θα υπάρχει κάποια μεγάλη διακοπή παροχής ισχύος. Σε αυτό το κεφάλαιο παρουσιάζονται οι πιο γνωστές μέθοδοι αποθήκευσης. / During the last few years, under the pressure of the increased burden on the environment due to the use of fossil fuels and in fear of great climate changes which we all have already witnessed, the use of ecological and environmentally friendly energy solutions has already been widely discussed. Consequently ,billions have been spent and research has been conducted, in the development of new forms of renewable energy sources and in performance optimization of the existing ones. A widely used renewable energy source, which has been also develop in our country(under the fear of fines from the European Union and not because of the development of environmental conscience), is the technology of photovoltaic systems(PV). PV is a quite known to scientists and to research teams renewable energy source, which efforts have reduced the cost of PV in such levels, that an investment in those systems would be proved cost effective even for the owner of low capitals. The energy produced from a PV string is not directly exploited for use, since the produced dc voltage is not appropriate neither for distribution from the public electrical grid, nor for use from the loads,which operate under conditions of ac voltage.Consequently a photovoltaic string could be connected to the grid, only if it is equipped with appropriate devices, which allow the proper conversion and optimum control of energy. The purpose of this work is the reference of the main structures, for the operation and management of grid-integrated photovoltaic systems.In particular the paper can be summurised as follows: Chapter 1: Power-Electronic Structures for the Grid Integration of Photovoltaic Systems A general reference in the existing inverter technologies and a general categorisation of the latter is presented. Chapter 2: Re view of Single-Phase Grid-Connected Inverters for Photovoltaic Modules Single-plase inverter topologies are presented, categorized, compared and evaluated against different characteristics. Chapter 3: Comparison of Photovoltaic Array Maximum Power Point Tracking Techniques The functioning of photovoltaic arrays to the maximum power point is necessary, in order to be considered profitable an investment in photovoltaic systems. Many such techniques available, are being reviewed. Chapter 4: Voltage Fluctuations on Distribution Level Introduced by Phtovoltaic Systems Photovoltaic elements convert solar energy to electric, and consequently their electric generation is directly dependant on climatic conditions. The present analysis describes forecasting methods of fluctuations in solar irradiance which also results in fluctuations in the generated voltage. Chapter 5: Storage Systems Every electrical energy system, in order to be considered fully integrated, must store excessive energy produced during certain time periods, and support with it critical loads, during mains’ power interruption.This last chapter contains the most widespread storage techniques.