73 research outputs found
Optimum design of a high frequency single phase inverter for the interconnection of small power PV systems with the low voltage network
No full textThe scope of the present work is to contribute in the sector of the Dispersed Power Generation PV systems with the development of an inverter that will be used for the interconnection of small PV generators with the electric network of urban regions. In more details the development of an inverter with electrical isolation is investigated which on the one hand it will ensure high power factor regulation and high efficiency for wide power range and on the other hand it will be characterised by simple power electronic circuit structure in order to ensure high reliability. Moreover, particular characteristics of this inverter should be the small volume and the small weight attributes very important considering its applications (incorporation in PV generators that will be placed in aspects or roofs of buildings). The interest of present work is focused in the high frequency current source Flyback inverter. For this topology two different control techniques were investigated leading to different operation modes. Moreover, their suitability is studied for different power levels. For both control techniques mathematic models were developed connecting the transferred power in the public grid with the inverter operational parameters as well as criteria for the inverter safe operation area were exported considering the acceptable peak voltage and current values for the semiconductor switches. Moreover, the combined application of two control techniques is proposed and an optimum inverter design strategy is presented aiming to the development of an inverter with the smallest possible volume as well as to the achievement of high power factor regulation and high efficiency for wide power range Last but not least a current pulsation smoothing active filter is investigated and developed which permits the elimination of the low frequency inverter input current. The current pulsation is a result of the power pulsation due to the single phase power generation and its elimination is of great importance in order to exploit the maximum PV generated electricity power. The active filter configuration is independent from the inverter topology and its operation mode and hence it can be applied for various single stage topologies. The precision of the mathematic models the correctness of the proposed design strategy and the effectiveness of the proposed active filter are validated via simulation and experimental results. Finally, the conclusions of whole study are exhibited.Σκοπός της παρούσας εργασίας είναι η συμβολή της στον τομέα των φωτοβολταϊκών μονάδων διεσπαρμένης παράγωγης με την αναζήτηση μιας διάταξης διασύνδεσης Φ/Β γεννητριών μικρής ισχύος με το ηλεκτρικό δίκτυο των αστικών περιοχών. Συγκεκριμένα διερευνάται η δυνατότητα ανάπτυξης μιας ηλεκτρονικής διάταξης με απομόνωση η οποία αφ’ ενός μεν θα εξασφαλίζει υψηλό συντελεστή ισχύος και υψηλό βαθμό απόδοσης για ευρύ φάσμα λειτουργίας αφ’ ετέρου δε θα διέπεται από μικρό βαθμό πολυπλοκότητας στο κύκλωμα ισχύος της προκείμενου να εξασφαλίζεται υψηλή αξιοπιστία. Το ενδιαφέρον της εργασίας εστιάσθηκε στον υψίσυχνο αντιστροφέα ρεύματος τοπολογίας Flyback. Για τη διάταξη αυτή διερευνήθηκαν δύο διαφορετικές τεχνικές ελέγχου (οι οποίες οδηγούν σε διαφορετικές καταστάσεις λειτουργίας) και ελέγχθηκε η καταλληλότητά τους για διαφορετικά επίπεδα ισχύος. Για τις δυο αυτές τεχνικές ελέγχου αναπτύχθηκαν μαθηματικά μοντέλα που συνδέουν τη μεταφερομένη στο δίκτυο ισχύ με τις κατασκευαστικές παραμέτρους του αντιστροφέα και εξήχθησαν κριτήρια για τα ασφαλή όρια λειτουργίας του αντιστροφέα με γνώμονα την καταπόνηση των ημιαγωγικών στοιχείων ισχύος. Επιπλέον, προτάθηκε η συνδυασμένη εφαρμογή των δύο τεχνικών ελέγχου και παρουσιάστηκε μια στρατηγική σχεδιασμού του αντιστροφέα ώστε να γίνεται βέλτιστη επιλογή όλων των επιμέρους λειτουργικών του στοιχείων με ταυτόχρονη ελαχιστοποίηση του όγκου του, επίτευξη υψηλού συντελεστή ισχύος καθώς και υψηλού βαθμού απόδοσης για ευρύ φάσμα της παραγόμενης ισχύος. Τέλος, διερευνήθηκε η δυνατότητα ανάπτυξης ενός ενεργού φίλτρου για την αποτελεσματική εξομάλυνση της έντονης κυμάτωσης του ρεύματος εισόδου του προτεινομένου αντιστροφέα. Η κυμάτωση αυτή είναι αποτέλεσμα της τροφοδότησης του μονοφασικού ηλεκτρικού δικτύου Ε.Ρ. από τη συνεχή τάση και το συνεχές ρεύμα που παράγουν οι φωτογεννήτριες και ο περιορισμός της είναι ιδιάζουσας σημασίας προκείμενου να καταστεί δυνατή η αποδοτική λειτουργία της όλης διάταξης. Η λειτουργία του προτεινομένου ενεργού φίλτρου είναι ανεξάρτητη τόσο των καταστάσεων λειτουργίας του αντιστροφέα τύπου Flyback όσο και γενικότερα της τοπολογίας του αντιστροφέα καθιστώντας την έτσι ως μια ελκυστική λύση και για διαφορετικές τοπολογίες μετατροπέων. Η ακρίβεια των μαθηματικών μοντέλων, η ορθότητα της προτεινομένης στρατηγικής σχεδιασμού και η αποτελεσματικότητα του προτεινομένου ενεργού φίλτρου επιβεβαιώθηκαν μέσω προσομοίωσης και πειραματικών δοκιμών ενώ τέλος παρατίθενται τα συμπεράσματα από το σύνολο της εργασίας
The identification of road modality and occupancy patterns by Wi-Fi monitoring sensors as a way to support the “Smart Cities” concept: Application at the city centre of Dordrecht
No full textAs world urbanization continues apace and total population increases, there is an immediate demand for better monitoring and exploitation of space. In view of the above, the “Smart Cities” concept has been developed and numerous efforts are made to deploy technology to this end. The main information needed for city development and planning is road modality and the relevant occupancy patterns. However, it is quite difficult to collect this information. There have been several different approaches towards providing this information and various methods have been used. However, each of them has weaknesses which do not allow it to be used on its own. On the other hand, thanks to the new technological developments and due to the growing needs of society over the last years, the system of Wi-Fi monitoring sensors has been increasingly used in outdoor environments. Many companies have already used this method to collect data and provide information about users’ behavior in places such as public areas, shopping centers and malls. Nonetheless, the contribution of this thesis is the study of the applicability of this method, the assessment of the reliability of its outcomes and the identification of crucial parameters which significantly affect the final accuracy. Thus, the aim of this research is to investigate what kind of road modality and occupancy patterns can be recognized using Wi-Fi monitoring sensors in a city area as well as which setup parameters can influence the final outcome. The system is implemented in the city of Dordrecht, which constitutes the research area of this study. First of all, the design of the observation network is described and the relevant parameters are taken into account. Using the data collected by the system and the known distances between the sensors, the movement speed of each device is computed. Street-uses criteria of the research area are also used as input to the system, and in combination with the computed speed three categories of users are recognized and each device is categorized as “pedestrian”, “bicyclist”, or “vehicle”. Under this classification each street’s road modality is studied. The relationship between the categories throughout the day is investigated and preferred streets for each kind of users are recognized. Based on the ability of the system to identify every device in the research area throughout the day, the movement behaviors of users are researched and similarities between them as well and the most frequent patterns are identified. Three sets of movement patterns are studied considering the number of sensors which scan the same device within a time period. Each set is investigated separately for every kind of users. Moreover, using the number of devices scanned at each sensor point, occupancy patterns are identified both for users as a whole and for each user category separately. It is argued that this constitutes an important advantage of the system. Rush hours, recession periods and movement trends are recognized for the different days of the week as well as the occupancy relationship between the research area and its surroundings. Finally, a questionnaire and random samplings with Bernoulli trial are used to validate the outcomes. A quite strong correlation between the system’s results and reality is revealed, especially with regard to pedestrians and bicyclists. However, despite the quite promising findings, further implementation and testing of the system in different environments is needed in order to draw an indisputable conclusion about its effectiveness.Architecture and The Built EnvironmentOTBGeomatics for the Built Environmen
On the Implementation of the Nearly Zero Energy Building Concept for Jointly Acting Renewables Self-Consumers in Mediterranean Climate Conditions
No full textCost-effective energy saving in the building sector is a high priority in Europe; The European Union has set ambitious targets for buildings’ energy performance in order to convert old energy-intensive ones into nearly zero energy buildings (nZEBs). This study focuses on the implementation of a collective self-consumption nZEB concept in Mediterranean climate conditions, considering a typical multi-family building (or apartment block) in the urban environment. The aggregated use of PVs, geothermal and energy storage systems allow the self-production and self-consumption of energy, in a way that the independence from fossil fuels and the reliability of the electricity grid are enhanced. The proposed nZEB implementation scheme will be analyzed from techno-economical perspective, presenting detailed calculations regarding the components dimensioning and costs-giving emphasis on life cycle cost analysis (LCCA) indexes—as well as the energy transactions between the building and the electricity grid. The main outcomes of this work are that the proposed nZEB implementation is a sustainable solution for the Mediterranean area, whereas the incorporation of electrical energy storage units—though beneficial for the reliability of the grid—calls for the implementation of positive policies regarding the reduction of their payback period
The solutions of the 3rd and 4th Clay Millennium problems
No full textIn this treatise I present the solutions of the third Clay Millennium problem
in the computational complexity and the fourth Clay Millennium problem in
classical fluid dynamics.Comment: arXiv admin note: text overlap with arXiv:1108.1165 by other author
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Shared authority: courts and legislatures in legal theory
No full textThis book advances a fresh philosophical account of the relationship between the legislature and courts, opposing the common conception of law, in which it is legislatures that primarily create the law, and courts that primarily apply it. This conception has eclectic affinities with legal positivism, and although it may have been a helpful intellectual tool in the past, it now increasingly generates more problems than it solves. For this reason, the author argues, legal philosophers are better off abandoning it. At the same time they are asked to dismantle the philosophical and doctrinal infrastructure that has been based on it and which has been hitherto largely unquestioned. In its place the book offers an alternative framework for understanding the role of courts and the legislature; a framework which is distinctly anti-positivist and which builds on Ronald Dworkin’s interpretive theory of law. But, contrary to Dworkin, it insists that legal duty is sensitive to the position one occupies in the project of governing; legal interpretation is not the solitary task of one super-judge, but a collaborative task structured by principles of institutional morality such as separation of powers which impose a moral duty on participants to respect each other's contributions. Moreover this collaborative task will often involve citizens taking an active role in their interaction with the law
On the exploitation of dynamic simulations for the design of buildings energy systems
No full textTo achieve the Paris Agreement 1.5 °C target, apart from the obligation for new buildings to be ZEBs, the existing building stock should be retrofitted as well, in order to improve their energy efficiency by using more efficient electromechanical energy systems and envelope materials, whereas RES should cover their energy needs. In this context, Energy Performance Certificates (EPCs) have been institutionalized to certify the energy behavior of buildings. Various types of buildings energy modeling tools and calculation methods have been proposed for EPCs procedures. This study focuses on the energy performance gap between dynamic and quasi steady-state simulation tools. The results from a comparative case study have shown remarkable discrepancies between dynamic and quasi-steady-state simulation processes, for the same building. Indeed, the quasi-steady-state simulation tool estimates 4.5% higher annual electricity consumption per conditioned area for the existing building and approximately 74% less energy savings for the retrofitted one, leading to an overestimation of 85% in CO2 emissions prediction. Finally, compared to the analysis with the dynamic simulation tool, an increased retrofit cost, approximately by 19.7% (and thus 3 times higher payback period), is needed according to the results of the quasi-steady-state simulation tool, in order to achieve the same Energy classification
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