Ανάλυση και έλεγχος φωτοβολταϊκού συστήματος συνδεδεμένου σε DC φορτίο και στο δίκτυο μέσω μετατροπέων

Σκοπός της παρούσας εργασίας είναι ο έλεγχος και η ανάλυση ευστάθειας ενός φωτοβολταϊκού (Φ/Β) συστήματος που παρέχει ηλεκτρική ισχύ σε ένα τοπικό, μεταβαλλόμενο φορτίο συνεχούς ρεύματος και στο ηλεκτρικό δίκτυο μέσω μετατροπέων ισχύος. Για τον έλεγχο του συστήματος χρησιμοποιήθηκαν μη γραμμικοί αναλογικοί-ολοκληρωτικοί (proportional-integral, PI) ελεγκτές σε διαδοχική διάταξη (cascade control). Αξιοποιώντας κάποιες ιδιότητες του πλήρους μη γραμμικού συστήματος κλειστού βρόχου, παρατίθεται η απόδειξη της ευστάθειας σε δύο βήματα, όπως αυτή έχει πρόσφατα προταθεί στη διεθνή βιβλιογραφία. Στο πρώτο βήμα αποδεικνύεται η ιδιότητα της παθητικότητας (passivity) για το σύστημα. Στο δεύτερο βήμα, εφαρμόζεται η Lyapunov τεχνική στο γραμμικό υποσύστημα του συνολικού συστήματος. Συνδυάζοντας αυτά τα δυο βήματα, κατασκευάζεται μια σύνθετη συνάρτηση Lyapunov με την οποία αποδεικνύεται η ευστάθεια από είσοδο-προς-κατάσταση (input-to-state stability, ISS) του πλήρους μη γραμμικού συστήματος κλειστού βρόχου. Για την βαθύτερη κατανόηση της εργασίας, αρχικά γίνεται μια αναφορά στις Ανανεώσιμες Πηγές Ενέργειας, στο μοντέλο της Διεσπαρμένης Παραγωγής ενέργειας και στη φιλοσοφία των Μικροδικτύων. Ακολουθούν η παρουσίαση και συνοπτική ανάλυση των Μετατροπέων Ηλεκτρικής Ισχύος και των βασικών ενεργών δομικών τους στοιχείων που είναι τα Ημιαγωγά Διακοπτικά Στοιχεία. Στη συνέχεια, παρουσιάζονται λεπτομερώς τα χαρακτηριστικά της Φωτοβολταϊκής Τεχνολογίας. Επίσης, παρουσιάζονται οι αλγόριθμοι ανίχνευσης του Σημείου Λειτουργίας Μεγίστης Ισχύος για ένα Φ/Β σύστημα που ελέγχουν κατάλληλα τους μετατροπείς ισχύος ώστε να παρέχει το Φ/Β κάθε στιγμή τη μέγιστη δυνατή ισχύ. Στο τελευταίο σκέλος της εργασίας, παρατίθεται η απόδειξη για της ISS ευστάθειας του πλήρους Φ/Β συστήματος συνδεδεμένου με το ηλεκτρικό δίκτυο ενώ, τέλος, παρουσιάζονται τα αποτελέσματα της προσομοίωσης που πραγματοποιήθηκε σε περιβάλλον MATLAB/Simulink.The main purpose of this diploma thesis is the control and stability analysis of a photovoltaic ( PV) system providing, electrical power to a local switching dc load and grid, through power converters. To this end, linear proportional-integral (PI) controllers in cascade form were adopted. Based on some crucial properties of the linear closed-loop system, we present the stability proof in two steps as shown in international bibliography. In the first step, the passivity property for the system is achieved. In the second step, we apply Lyapunov techniques for the linear subsystem of the complete system. With the combination of these two steps, a composite Lyapunov function is constructed to prove the input-to-state (ISS) stability of the complete nonlinear closed-loop system. For a clearer understanding of this diploma thesis, an introduction in Renewable Resources, Distributed Generation model and in the concept of Microgrids is firstly made. Then, the main operation of Power Converters and Power Semiconductors Devices is presented , with the last devices constituting the basic elements in Power Converters operations. An extensive analysis of the Photovoltaic Technology is also made. Finally, the Maximum Power Point Tracking algorithms, used in PV systems in order to achieve the maximum power supply, are presented. In the last section of this diploma thesis the input-to state (ISS) stability analysis of the grid-connected PV system is presented as well as the simulation results in Matlab/Simulink.Παππάς Λ. Βασίλειο

Reactive Semantic Planning in Unexplored Semantic Environments Using Deep Perceptual Feedback

This paper presents a reactive planning system that enriches the topological representation of an environment with a tightly integrated semantic representation, achieved by incorporating and exploiting advances in deep perceptual learning and probabilistic semantic reasoning. Our architecture combines object detection with semantic SLAM, affording robust, reactive logical as well as geometric planning in unexplored environments. Moreover, by incorporating a human mesh estimation algorithm, our system is capable of reacting and responding in real time to semantically labeled human motions and gestures. New formal results allow tracking of suitably non-adversarial moving targets, while maintaining the same collision avoidance guarantees. We suggest the empirical utility of the proposed control architecture with a numerical study including comparisons with a state-of-the-art dynamic replanning algorithm, and physical implementation on both a wheeled and legged platform in different settings with both geometric and semantic goals. For more information: Kod*la

Waveform Modelling for the Laser Interferometer Space Antenna

LISA, the Laser Interferometer Space Antenna, will usher in a new era in gravitational-wave astronomy. As the first anticipated space-based gravitational-wave detector, it will expand our view to the millihertz gravitational-wave sky, where a spectacular variety of interesting new sources abound: from millions of ultra-compact binaries in our Galaxy, to mergers of massive black holes at cosmological distances; from the beginnings of inspirals that will venture into the ground-based detectors' view to the death spiral of compact objects into massive black holes, and many sources in between. Central to realising LISA's discovery potential are waveform models, the theoretical and phenomenological predictions of the pattern of gravitational waves that these sources emit. This white paper is presented on behalf of the Waveform Working Group for the LISA Consortium. It provides a review of the current state of waveform models for LISA sources, and describes the significant challenges that must yet be overcome.Comment: 239 pages, 11 figures, white paper from the LISA Consortium Waveform Working Group, invited for submission to Living Reviews in Relativity, updated with comments from communit

Waveform modelling for the Laser Interferometer Space Antenna

LISA, the Laser Interferometer Space Antenna, will usher in a new era in gravitational-wave astronomy. As the first anticipated space-based gravitational-wave detector, it will expand our view to the millihertz gravitational-wave sky, where a spectacular variety of interesting new sources abound: from millions of ultra-compact binaries in our Galaxy, to mergers of massive black holes at cosmological distances; from the early inspirals of stellar-mass black holes that will ultimately venture into the ground-based detectors’ view to the death spiral of compact objects into massive black holes, and many sources in between. Central to realising LISA’s discovery potential are waveform models, the theoretical and phenomenological predictions of the pattern of gravitational waves that these sources emit. This White Paper is presented on behalf of the Waveform Working Group for the LISA Consortium. It provides a review of the current state of waveform models for LISA sources, and describes the significant challenges that must yet be overcome

Search for eccentric black hole coalescences during the third observing run of LIGO and Virgo

Despite the growing number of confident binary black hole coalescences observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that were already identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total mass M>70 M⊙) binaries covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place an upper limit for the merger rate density of high-mass binaries with eccentricities 0<e≤0.3 at 0.33 Gpc−3 yr−1 at 90\% confidence level