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

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

Σκοπός της παρούσης διπλωματικής εργασίας είναι η μελέτη μιας ανεμογεννήτριας με επαγωγική μηχανή δακτυλιοφόρου δρομέα με διασύνδεση συνεχούς ρεύματος στο δίκτυο. Η διασύνδεση συνεχούς ρεύματος αποτελείται από έναν πυκνωτή που είναι συνδεδεμένος με την πλευρά της μηχανής μέσω ενός ac/dc πλήρως ελεγχόμενου ανορθωτή ισχύος ενώ με την πλευρά του δικτύου συνδέεται μέσω ενός dc/ac πλήρως ελεγχόμενου αντιστροφέα ισχύος. Ο πυκνωτής , ο ανορθωτής και ο αντιστροφέας είναι συνδεδεμένοι σε σειρά και αποτελούν την dc διασύνδεση. Η μελέτη γίνεται αρχικά με την θεωρητική ανάλυση του συστήματος της ανεμογεννήτριας. Για την θεωρητική ανάλυση χρησιμοποιείται για διευκόλυνση ο μετασχηματισμός Park που μετασχηματίζει το τριφασικό a-b-c σύστημα των εξισώσεων του συστήματος στο d-q πλαίσιο αναφοράς. Η ανάλυση μας οδηγεί στην εξαγωγή των εξισώσεων στον χώρο κατάστασης και έτσι οδηγούμαστε στο μαθηματικό μοντέλο του συστήματος. Στην συνέχεια παρουσιάζεται η θεωρία ελέγχου του συστήματος της επαγωγικής γεννήτριας και γίνεται ο προσδιορισμός των κερδών των cascaded PI ελεγκτών. Στο τελικό στάδιο της διπλωματικής εργασίας γίνεται η προσομοίωση του συστήματος και της συμπεριφοράς του κατά την μεταβολή του ανέμου. Ο άνεμος στην πρώτη περίπτωση μεταβάλλεται βηματικά και στην δεύτερη περίπτωση με τυχαίο τρόπο. Με την χρήση του λογισμικού Simulink του Matlab εξάγουμε τις γραφικές παραστάσεις των χαρακτηριστικών μεγεθών : ρευμάτων, τάσεων, ροών, ισχύων του συστήματος και παρατηρώντας τα αποτελέσματα αυτών καταλήγουμε σε σχετικά συμπεράσματα για το προς μελέτη σύστημα. / The purpose of this thesis is to study a wind turbine with a wound rotor induction generator which is connected to the network with a dc link. The dc link is made of a capacitor which is connected to the side of the machine with a fully controlled ac/dc power rectifier and to the network side with a fully controlled dc/ac inverter. The capacitor, the rectifier and the inverter are connected in series and comprise the dc link. Firstly, it is necessary to begin with the theoretical analysis of the system of the wind turbine. At the system analysis is used the Park transformation that transforms the three-phase a-b-c system of equations at the d-q reference frame. Our analysis leads to be exported the equations in state space which are the mathematical model of the system. Then we present the cascaded PI controller design and the gain tuning for the system of the wound rotor induction generator. In the final stage of the thesis there is the simulation of the system and its behavior during the change of wind. In the first case, the wind change stepwise and in the second case in a random manner. By using the software of Simulink at Matlab we draw the graphs of feature sizes such as: currents , voltages , flows and power of the system and as we observe the results of the graphs we arrive at conclusions about the under study system.

Η παρούσα διπλωματική εργασία κάνει μια ανασκόπηση στην ενεργειακή κατάσταση του πλανήτη και της Ελλάδας. Παρουσιάζει τις εναλλακτικές-ανανεώσιμες μορφές ενέργειας παραγωγής ηλεκτρισμού. Στη συνέχεια, αναλύει τον άνεμο, τα χαρακτηριστικά μεγέθη του, την αιολική ενέργεια, και τις προοπτικές της εγχώρια. Βλέπουμε αναλυτικά τον ανεμοκινητήρα, τους διαφορετικούς τύπους του και τη λειτουργία του. Και καταλήγουμε στο να καθορίσουμε τους τρόπους αξιολόγησης μιας αιολικής εγκατάστασης, εκφράζουμε μαθηματικά τις οικονομικές σχέσεις και παραθέτουμε μια εφαρμογή αιολικής εγκατάστασης που αναλύεται με τα παραπάνω. Τέλος, αναφερόμαστε στο νομοθετικό πλαίσιο αν και ρευστό από έτος σε έτος και στην ισχύουσα διαδικασία εγκατάστασης ενός αιολικού πάρκου. / The present dissertation gives a general review of the situation of energy of the planet and Greece. It presents the alternative-renewable forms of energy for the production of electricity. Afterwards, it analyses the wind, its characteristic sizes, the wind power and its domestic perspectives. We can see in detail the wind engine , its various types and its function. Furthermore, we end up defining the ways evaluating of a wind installation, we express mathematically the financial relations and we not only cite an application of a wind installation which is analysed with the above mentioned ways but we also present the easiest analysis through the computer. Finally, we refer to the legislative scope even though it is unstable from year to year and to the procedure of installation of a wind park which is in effect.

The U.S. Navy has developed in their ships, and is continually improving, electric propulsion, ship service power, and electric loads. The latest topology under design is the integrated power system (IPS). The IPS entails the all electric ship concept with electric propulsion, direct current (DC) distribution, and modular technology. In the all electric ship concept, ship propulsion and ship service loads are powered by alternating current (AC) generation. For the IPS, power electronics conversion is to be utilized to convert alternating current (AC) generation to direct current (DC) distribution. As state-of-the-art power electronics, the Navy plans to use power electronic building blocks (PEBB) technology in its IPS. A U.S. naval shipboard power system is required to be a highly reconfigurable system to enhance its survivability and reliability. Reconfiguration is a change in the shipboard power system state for various reasons such as new topology, changing missions and emergencies. It was decided to study the behavior of a PEBB-based integrated shipboard power system during reconfiguration. Since no real time operation data was available, the problem was studied through the simulation of reconfiguration scenarios on a scaled-down computer model of an IPS in MATLAB. Reconfiguration scenarios were determined and staged, and an AC/DC power system stability assessment methodology was applied by decoupling the IPS test system around an intrazonal bus. The coupled system of the test IPS, consisted of two dynamic 4160 VAC generators, two rectifiers, two DC-DC converters between the rectifiers' output looped bus and the downstream intrazonal 775V busses, inverters, buck converters, AC loads and DC loads. There was modeling of excitation perturbations which introduced errors in the assessment of the stability requiring an approximation analysis. The study found that the DC bus of interest was stable for all nine reconfiguration scenarios staged, but it found that other busses were not stable for two of the scenarios. The study further found that lower stability margins occurred at lower frequencies of about 1Hz for stable scenarios. It concluded that there were tangible benefits to advancing the shipboard power system architecture to the IPS topology because of the good stability results.

Electric power systems are huge real time energy distribution networks where accurate short term load forecasting (STLF) plays an essential role. This thesis is an effort to comprehensively investigate new and advanced neural network (NN) architectures to perform STLF. Two hybrid and two 3-layered NN architectures are introduced. Each network is individually tested to generate weekday and weekend forecasts using data from three jurisdictions of Canada. Overall findings suggest that 3-layered cascaded NN have outperformed almost all others for weekday forecasts. For weekend forecasts 3-layered feed forward NN produced most accurate results. Recurrent and hybrid networks performed well during peak hours but due to occurrence of constant high error spikes were not able to achieve high accuracy.

Generation loss contingencies in electric power systems result in a deviation of system frequency from nominal, a condition which must be corrected promptly in order to prevent further degradation of the power system. Automatic load-shedding using underfrequency relays is one of the techniques used to correct abnormal frequency deviations and prevent the risk of uncontrolled outages. If sufficient load is shed following a contingency to preserve interconnections and keep generators on-line, the system can be restored with relative speed and ease. On the other hand, if a declining frequency condition is not dealt with adequately, a cascading disconnection of generating units may develop, leading to a possible total system blackout. / This thesis develops and tests a new systematic method for setting underfrequency relays offering a number of advantages over conventional methods. A discretized swing equation model is used to evaluate the system frequency following a contingency, and the operational logic of an underfrequency relay is modeled using mixed integer linear programming (MILP) techniques. The proposed approach computes relay settings with respect to a subset of all plausible contingencies for a given system. A method for selecting the subset of contingencies for inclusion in the MILP is presented. The goal of this thesis is to demonstrate that given certain types of degrees of freedom in the relay setting problem, it is possible to obtain a set of relay settings that limits damage or disconnection of generating units for each and every possible generation loss outage in a given system, while attempting to shed the least amount of load for each contingency.

This thesis presents a method of detecting electrical islands in low voltage distributed generator networks by measuring negative sequence impedance differences between islanded and utility connections. Extensive testing was conducted on a commercial building and 25 kV distributed generator fed network by measuring naturally occurring and artificially injected negative sequence components. Similarly, this technique was tested using the IEEE 399-1990 bus test case using the EMTP software. The practical measurements have been matched to simulations where further system performance characteristics of detecting power system islands has been successfully demonstrated. Measured results indicate that unbalanced load conditions are naturally occurring and readily measurable while deliberately unbalanced loads can increase the accuracy of negative sequence impedance islanding detection. The typically low negative sequence impedance of induction motors was found to have only a small effect in low voltage busses, though large machines can effect the threshold settings. Careful placement of the island detector is required in these situations. The negative sequence impedance measurement method is an improvement on previous impedance measurement techniques for islanding detection due to its accuracy, and distinctly large threshold window which have challenged previous impedance based islanding detection techniques.

No description available.

No description available.