• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 2
  • 2
  • 2
  • 1
  • Tagged with
  • 9
  • 9
  • 8
  • 4
  • 4
  • 4
  • 3
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Methods to Mitigate Harmonics in Residential Power Distribution Systems

Bagheri, Pooya Unknown Date
No description available.
2

Υβριδικό ενεργό φίλτρο μέσης τάσης που χρησιμοποιεί μετατροπέα τριών επιπέδων και συνδέεται απευθείας στο δίκτυο χωρίς να παρεμβάλλεται μετασχηματιστής

Βασσάκης, Εμμανουήλ 14 February 2012 (has links)
Ένα από τα πιο σύγχρονα προβλήματα στα συστήματα Ηλεκτρικής Ενέργειας είναι οι αρμονικές ρεύματος. Γενικά, η αρμονική μιας κύμανσης είναι μια συνιστώσα συχνότητας του σήματος, η οποία είναι ακέραιο πολλαπλάσιο της θεμελιώδους συχνότητας, π.χ. εάν η θεμελιώδης συχνότητα είναι f, οι αρμονικές έχουν συχνότητες 2f,3f,4f και ούτω κάθε εξής. Για το ηλεκτρικό σήμα, η θεμελιώδης συχνότητα είναι τα 50 Hz. Άρα, οι αρμονικές του ηλεκτρικού ρεύματος έχουν συχνότητες ακέραια πολλαπλάσια της θεμελιώδους συχνότητας. Παραδείγματος χάρη, 100 Hz είναι η αρμονική δεύτερης τάξης, 150 Hz είναι η αρμονική τρίτης τάξης, 200 Hz είναι η αρμονική τέταρτης τάξης και ούτω κάθε εξής. Αιτία ύπαρξης αρμονικών ρεύματος είναι η ύπαρξη μη γραμμικών φορτίων, φορτίων δηλαδή, που παίρνουν ρεύμα διαφορετικής κυματομορφής από την τάση, άγουν δηλαδή ρεύμα μόνο σε ορισμένες περιοχές της τάσης. Τα προβλήματα που δημιουργούν οι αρμονικές είναι: α) μείωση του συντελεστή ισχύος με αποτέλεσμα αυξημένες απώλειες στα καλώδια, β) φαινόμενα συντονισμού με συνέπεια την καταστροφή πυκνωτών και μετασχηματιστών, γ) αρμονική παραμόρφωση τάσης η οποία οδηγεί σε αύξηση απωλειών σε κινητήρες, δ) παρεμβολές σε κυκλώματα ελέγχου και τηλεπικοινωνιών, ε) λανθασμένη λειτουργία συσκευών προστασίας, ζ) καταπόνηση ηλεκτρικών συσκευών. Όλα τα παραπάνω δημιουργούν υποβάθμιση της ποιότητας ισχύος. Και αν λάβουμε υπόψη την αυξανόμενη χρήση μη γραμμικών φορτίων τότε η βελτίωση της ποιότητας ισχύος είναι επιτακτική στην σημερινή εποχή. Για την αντιμετώπιση των αρμονικών ρεύματος, χρησιμοποιούμε αρμονικά φίλτρα. Τα αρμονικά φίλτρα χωρίζονται σε τρείς κατηγορίες. Υπάρχουν τα παθητικά φίλτρα, τα ενεργά φίλτρα και τα υβριδικά φίλτρα. Τα παθητικά αρμονικά φίλτρα που αποτελούνται από πυκνωτές, επαγωγές και αντιστάσεις μπορούν να χωριστούν σε φίλτρα συντονισμού και σε υψιπερατά φίλτρα. Αυτά συνδέονται παράλληλα με τα μη γραμμικά φορτία. Τα ενεργά φίλτρα μπορούν να χωριστούν σε παράλληλα ενεργά φίλτρα και σε εν σειρά ενεργά φίλτρα ανάλογα με την κυκλωματική τους διαμόρφωση. Προς το παρόν, τα παράλληλα ενεργά φίλτρα είναι πιο ελκυστικά από τα εν σειρά ενεργά φίλτρα, όσον αφορά την μορφή και την λειτουργία τους. Το παράλληλο ενεργό φίλτρο μπορεί να ελεγχθεί με βάση τον παρακάτω τρόπο ελέγχου. Ο ελεγκτής παρατηρεί το στιγμιαίο ρεύμα του φορτίου. Αποσπά το αρμονικό ρεύμα από το υπό παρατήρηση ρεύμα του φορτίου δια μέσου της ψηφιακής επεξεργασίας του σήματος. Το ενεργό φίλτρο τροφοδοτεί το φορτίο με το αρμονικό ρεύμα που χρειάζεται για να λειτουργήσει σωστά, με συνέπεια να απαλλάσσεται η πηγή τροφοδοσίας από το αρμονικό ρεύμα. Διαφορετικά από το παράλληλο ενεργό φίλτρο, το εν σειρά ενεργό φίλτρο ελέγχεται με βάση τον παρακάτω τρόπο ελέγχου. Ο ελεγκτής παρατηρεί το στιγμιαίο ρεύμα τροφοδοσίας. Αποσπά το αρμονικό ρεύμα από το υπό παρακολούθηση ρεύμα τροφοδοσίας δια μέσου της ψηφιακής επεξεργασίας του σήματος. Το ενεργό φίλτρο εφαρμόζει μια τάση εξισορρόπησης ανάλογη του αρμονικού ρεύματος και αντίθετου πρόσημου επί του πρωτεύοντος του μετασχηματιστή που είναι συνδεδεμένος σε σειρά με την πηγή τροφοδοσίας. Αυτό έχει ως αποτέλεσμα την σημαντική μείωση του αρμονικού ρεύματος τροφοδοσίας. Τα υβριδικά φίλτρα είναι ένας συνδυασμός ενός παθητικού φίλτρου και ενός ενεργού φίλτρου. Μια υβριδική διάταξη που είναι πολύ δημοφιλής είναι η εν σειρά σύνδεση ενός ενεργού φίλτρου και ενός παθητικού φίλτρου. Γενικά, τα υβριδικά φίλτρα έχουν πλεονεκτήματα σε σχέση με τα ενεργά φίλτρα. Μερικά από αυτά είναι: α) εμφάνιση μικρότερης τάσης στον πυκνωτή του φίλτρου, β) χρησιμοποίηση μικρότερης τάσης IGBTs ως στοιχεία ισχύος, γ) μη εμφάνιση της δεσπόζουσας αρμονικής της τάσης στα άκρα του ενεργού φίλτρου, δ) μικρότερης έντασης διακοπτικές αιχμές, ε) καλύτερη εκτέλεση φιλτραρίσματος. Στην συγκεκριμένη διπλωματική εργασία εξετάζεται ένα υβριδικό ενεργό φίλτρο μέσης τάσης που χρησιμοποιεί μετατροπέα τριών επιπέδων και συνδέεται απευθείας στο δίκτυο χωρίς να παρεμβάλλεται μετασχηματιστής. Η υπό μελέτη διάταξη αποτελείται από την πηγή τροφοδοσίας, η οποία είναι ονομαστικής τάσεως 4.16 KV (πολική τάση, rms τιμή) και συχνότητας 60 Hz. Επίσης η επαγωγή της πηγής τροφοδοσίας είναι Ls=0.15 mH. Το μη γραμμικό φορτίο της διάταξης μας είναι μια ανορθωτική διάταξη διόδων, όπου στην AC πλευρά της έχει τοποθετηθεί μία επαγωγή LAC για καλύτερη προστασία ρεύματος. Το υβριδικό ενεργό φίλτρο συνδέεται απευθείας στο φορτίο χωρίς την χρήση μετασχηματιστή υποβίβασης της τάσης. Αυτή η συγκεκριμένη υβριδική διάταξη αποτελείται από ένα παθητικό φίλτρο που είναι συντονισμένο στην έβδομη αρμονική συχνότητα και ένα ενεργό αρμονικό φίλτρο. Το ενεργό και παθητικό φίλτρο συνδέονται σε σειρά. Το ενεργό φίλτρο χρησιμοποιεί μετατροπέα τριών επιπέδων. Η προσομοίωση της συγκεκριμένης διάταξης γίνεται με το πρόγραμμα PSCAD. Τα αποτελέσματα δείχνουν ότι με την ενεργοποίηση του υβριδικού φίλτρου η κυματομορφή του ρεύματος τροφοδοσίας γίνεται σχεδόν ημιτονοειδής. Επίσης, βλέπουμε στο φάσμα με τις αρμονικές συχνότητες του ρεύματος τροφοδοσίας ότι είναι απαλλαγμένο από αρμονικές συχνότητες. Επομένως, η συγκεκριμένη διάταξη προσφέρει καλή εκτέλεση φιλτραρίσματος για εφαρμογές μέσης τάσης. / One of the most outstanding problems in Power Systems is the harmonic current. Generally, a harmonic fluctuation is a component frequency of the signal, which is an integer multiple of the fundamental frequency, e.g. if the fundamental frequency is f, the harmonics have frequency 2f, 3f, 4f, and so forth. For the electrical signal, the fundamental frequency is 50 Hz. Therefore, the harmonics of the power frequencies are integer multiples of the fundamental frequency. For example, 100 Hz is the second order harmonic, 150 Hz is the third order harmonic, 200 Hz is the fourth harmonic order and so on. Reason being harmonic current is the presence of nonlinear loads, i.e. loads that getting a current waveform which is different from the voltage waveform, i.e. drag power only in certain areas of tension. The problems caused by harmonics are: a) reducing the power factor that resulting to increased losses in the cable b) resonance resulting in the destruction of capacitors and transformations, c) harmonic voltage distortion which leads to increased losses in motors, d) interferences to control circuits and telecommunications, e) incorrect operation of protective devices, g) harassment of the electrical devices. All these cause degradation of power quality. And considering the increasing use of nonlinear loads, the improve of power quality is imperative in this era. To meet the harmonic current, using harmonic filters. Harmonic filters are divided into three categories. There are passive filters, active filters and hybrid filters. The passive harmonic filters consisting of capacitors, inductors and resistors can be divided into coordination filters and high pass filters. These are connected in parallel with nonlinear loads. Active filters can be divided into parallel active filters and series active filters in terms of the circuit configuration. At present, the parallel active filters are more attractive than the series active filters, in terms of form and function. The parallel active filter can be controlled by the following way. The controller observes the instantaneous load current. It extracts the harmonic current from the observed load current through the digital signal processing. The active filter supplies the load with harmonic current which needs to function properly, thus the power source exempt from the harmonic current. Different from the parallel active filter, the series active filter is controlled by the following way. The controller observes the instantaneous supply current. It extracts the harmonic current from the supply current through the digital signal processing. The active filter applies a voltage which is proportional to the harmonic current and opposite sign on the primary of the transformer which is connected in series with the power source. This results in significant reduction of the harmonic supply current. Hybrid Filters are a combination of a passive filter and an active filter. A very popular hybrid device is the series connection of an active filter and a passive filter. Generally, hybrid filters have advantages over active filters. Some of these are: a) show less voltage in the capacitor of the filter, b) using lower voltage-rated IGBTs as power devices, c) non-appearance of the dominant harmonic voltage at the ends of the active filter, d) less intense switching spikes, e) better filtering performance. In this thesis examined a medium-voltage transformerless hybrid active filter with three-level converter. The device under study consists of the power source, which has rated voltage 4.16 KV (polar voltage, rms value) and frequency 60 Hz. Also, the induction power source is Ls = 0.15 mH. The non-linear load is a diode rectifier device, where in the AC side has placed an induction of LAC to better protection of current. The hybrid active filter is connected directly to the load without the use of voltage step-down transformer. This particular hybrid device consists of a passive filter which is tuned to the seventh harmonic frequency, and an active harmonic filter. The active and passive filter are connected in series. The active filter uses a three-level inverter. The simulation of this device realized with the program PSCAD. The results indicate that after the activation of the hybrid filter, the power supply waveform is almost sinusoidal. Also see the spectrum with the harmonics of the supply current that is free from harmonics. Therefore, this device offers good performance filtering in medium voltage applications.
3

Modeling, Measurement and Mitigation of Power System Harmonics

Nassif, Alexandre Unknown Date
No description available.
4

Modeling, Measurement and Mitigation of Power System Harmonics

Nassif, Alexandre 11 1900 (has links)
Power system harmonics and interharmonics are power quality concerns that have received a great deal of attention in recent years. These phenomena can have several adverse effects on power system operation. The main harmonic and interharmonic sources are devices based on power electronics. An emerging class of harmonic sources is comprised of power electronic-based home appliances. These appliances are dispersed throughout the low-voltage distribution system, and their collective impact can result in unacceptable levels of voltage distortion. The characterization of home appliances based on their harmonic currents is an important step toward understanding the impact of these devices. This thesis presents an evaluation of the relative severity of the harmonic currents from these devices, and the impact of the disparity of the harmonic current phase angles. Typically, the voltage supplied to each harmonic source is already distorted. This distortion causes a change of the harmonic current magnitudes (traditionally referred to as the attenuation effect). Common harmonic analysis methods cannot take this variation into account because they use a typical harmonic current source model specified by a supply voltage having little or no distortion. This thesis characterizes the harmonic attenuation effect of power electronic-based appliances. One of the findings is that harmonic amplification, rather than attenuation, can occur under credible voltage conditions. This finding had not been made previously. In order to include the harmonic attenuation/amplification in appliance modeling, a measurement-based harmonic modeling technique is proposed. One of the most economic and effective ways to mitigate harmonics in power systems is through the use of harmonic shunt passive filters. These filters can be of many topologies. Selecting these topologies is a task that, today, depends on the experience and judgment of the filter designer. An investigation is carried out on the common filter topologies, and the most cost-effective topologies for mitigating harmonics are identified. As many of the larger harmonic loads also generate interharmonics, interharmonics have become prevalent in today’s medium-voltage distribution system. Mitigation cannot be carried out until the interharmonic-source location is known. A method for interharmonic source determination is proposed and then verified through simulation and field measurement studies.
5

Σχεδιασμός παθητικών αρμονικών φίλτρων

Ασιλιάν, Ορέστης 15 April 2013 (has links)
Η ραγδαία ανάπτυξη των ηλεκτρονικών ισχύος τα τελευταία χρόνια και η χρήση τους σε μια ποικιλία βιομηχανικών εφαρμογών οδήγησε στο πρόβλημα των ανώτερων αρμονικών. Η ύπαρξη ανώτερων αρμονικών επιφέρει πολλά προβλήματα στα συστήματα ηλεκτρικής ενέργειας και στα στοιχεία που τα αποτελούν. Για το λόγο αυτό, τοποθετούνται παθητικά φίλτρα που σκοπό έχουν να μειώσουν έως και να εξαλείψουν τις συνέπειες των αρμονικών. Ο σχεδιασμός των παθητικών αρμονικών φίλτρων μπορεί να γίνει με βάση διάφορα κριτήρια. Στην παρούσα διπλωματική εργασία, γίνεται σχεδιασμός παθητικών αρμονικών φίλτρων με τη βοήθεια των γενετικών αλγορίθμων που σκοπό έχουν τη μεγιστοποίηση του συντελεστή ισχύος. Η μεγιστοποίηση του συντελεστή ισχύος γίνεται αυξάνοντας την ωφέλιμη ισχύ (την ισχύ της θεμελιώδους αρμονικής), μειώνοντας τη μιγαδική ισχύ και εξαλείφοντας την ισχύ των ανώτερων αρμονικών (απώλειες). Πιο συγκεκριμένα: Στο 1ο κεφάλαιο γίνεται μια εισαγωγή στο πρόβλημα των ανώτερων αρμονικών καθώς και στις επιπτώσεις τους σε διάφορα τμήματα του εξοπλισμού ενός συστήματος ηλεκτρικής ενέργειας. Επίσης αναφέρεται συνοπτικά ο σκοπός των αρμονικών φίλτρων και της διπλωματικής εργασίας. Στο 2ο κεφάλαιο γίνεται εκτενής αναφορά στα παθητικά αρμονικά φίλτρα και σε θέματα που σχετίζονται με τα είδη, το μέγεθος, το κόστος, το σχεδιασμό και την προστασία των φίλτρων. Επιπλέον γίνεται μνεία στα όρια των αρμονικών βάσει του προτύπου 519-1992 του ΙΕΕΕ. Το 3ο κεφάλαιο γράφτηκε με σκοπό να αποτελέσει ένα εγχειρίδιο γενετικών αλγορίθμων. Ξεκινά με την ιστορική αναδρομή και γενικές έννοιες και επεκτείνεται σε ένα ευρύ φάσμα εφαρμογών. Επιπλέον γίνεται επεξήγηση των δυνατοτήτων του GA toolbox του Matlab καθώς και τα βήματα που θα πρέπει να ακολουθήσει κάποιος προκειμένου να χρησιμοποιήσει τους γενετικούς αλγορίθμους ως εργαλείο βελτιστοποίησης. 2 Στο 4ο κεφάλαιο γίνεται αναλυτική περιγραφή του συστήματος και των δεδομένων του, αποδεικνύεται το μαθηματικό μοντέλο που χρησιμοποιήσαμε και γίνεται αναφορά στα μεγέθη που θα υπολογιστούν. Επιπροσθέτως, παρουσιάζονται τα αποτελέσματα που προέκυψαν από τους γενετικούς αλγορίθμους για την περίπτωση των αρμονικών πηγής τάσης και για αυτή των αρμονικών πηγής ρεύματος έτσι ώστε να μεγιστοποιείται ο συντελεστής ισχύος. Τέλος, στο 5ο κεφάλαιο εξάγονται χρήσιμα συμπεράσματα τα οποία απορρέουν από το σχεδιασμό των παθητικών αρμονικών φίλτρων με τη χρήση των γενετικών αλγορίθμων έτσι ώστε να μεγιστοποιείται ο συντελεστής ισχύος. Εν κατακλείδι, αναφέρονται κάποιες μελλοντικές σκέψεις σχετικά με το σχεδιασμό παθητικών αρμονικών φίλτρων. / The rapid development of power electronics in recent years and their use in a variety of industrial applications led to the problem of higher harmonics. The existence of higher harmonics causes many problems in power electric systems and the elements they consist of. This is the reason why passive filters which are designed in order to reduce or even eliminate the effects of higher harmonics are used. The design of passive filters is based on various criteria. This Thesis, examines the design of passive harmonic filters (using genetic algorithms), which aim to maximize power factor. By increasing the useful power (power of fundamental harmonic), decreasing the apparent power and eliminating the power of higher harmonics (losses), the power factor is being maximized. More specific: The first chapter is an introduction to the problem of higher harmonics, as well as to their effects on various parts of electric power system equipment. There is also a summary of the purpose of harmonic filters and this thesis. In the second chapter extensive references are made on passive harmonic filters and issues relating to species, size, cost, design and protection of filters. In addition, reference is made to harmonic bounds, based on IEEE Standard 519-1992. The third chapter is written in order to serve as a handbook of genetic algorithms. It enters with the historical background of genetic algorithms and extends to their use on a wide range of applications. The potentials of Genetic Algorithm (GA) toolbox of Matlab are explained. The steps to be followed in order to use genetic algorithms as optimization tool are also mentioned. A detailed description of the system and its data is given in the fourth chapter. The mathematical model and its relations used to simulate our system are proved. An extensive reference is made to the units sizes that will be calculated. Additionally, the results obtained from the genetic algorithms both in the case of the harmonic voltage source and the harmonic current source, in order to maximize the power factor, are presented. Finally, in the fifth chapter, useful conclusions are drawn from the design of passive harmonic filters (using genetic algorithms). In addition some thoughts about alternative designs of passive harmonic filters are stated in this chapter.
6

Electro-mechanical modelling of tidal arrays

Sousounis, Marios Charilaos January 2018 (has links)
The aim of this study is to present, compare and improve the options of power transmission for tidal current arrays. The potential to generate low or zero carbon power from the world’s tides is increasing as technology moves forward. The technically available tidal current energy resource, the resource that can be captured using existing technology, in the United Kingdom can supply a significant amount of the UK electricity demand. Even though tidal current devices have similarities to offshore wind turbines in many aspects, a number of characteristics differentiate the approach needed regarding power transmission and drive-train design. Some of these characteristics are: predictable direction and speed of the tidal current, predetermined available area in a tidal channel, less swept area due higher density of water, continuous underwater operation and smaller distances to shore. This thesis is based on the hypothesis that tidal current energy can be harnessed using today’s technology in an efficient manner. Technology progression never stops and as new materials and methods become available the cost of utilising tidal current energy will drop in the years to come. However, the research question that has to be asked is whether using today’s technology tidal arrays can be an alternative source of electrical power. In order to respond to this research question electromechanical models of tidal current devices have been developed in detail, from resource to the grid connection, using mathematical linear and non-linear programming in MATLAB/Simulink. The tidal models developed include the tidal resource, the tidal turbine with pitch control, geared induction and synchronous generators, the power electronics with the generator controller, the grid side controller, the cables for power transmission, the filters and the grid connection. All the modelling aspects of this study are presented in Chapter 3. Single tidal current devices were compared using different generator technologies, squirrel cage induction generator or permanent magnet synchronous generator, and different location of the power converters, in the nacelle near the generator or many kilometres apart from the generator. Regarding the generator technology, results showed that even though differences are minor, the permanent magnet synchronous generators are more efficient. Regarding the location of the power converters results showed that positioning the power converters in the nacelle always yields fewer electrical losses but component accessibility is minimised due to the underwater operation of the tidal current device. A key focus aspect of the study is the power transmission option with onshore converters which is presented in detail. Using this concept it is possible to generate electricity from tidal current devices but at the same time keep the highest possible system reliability despite the continuous underwater operation. This concept has been used in the first demonstration tidal current arrays developed by Andritz Hydro Hammerfest. What is more, data provided by Andritz Hydro Hammerfest were utilised in order to validate the simulation models. In this study a step forward is taken regarding the concept of keeping the converter dry and controlling the tidal current generator from afar. An algorithm is developed to design power harmonic filters for systems that use long distance controls. Power harmonic filters allow the long distance control system to operate reliably under all conditions but generate significant electrical losses. The power harmonic filter design algorithm presented in this thesis estimates the exact filter parameters so that the filter ensures maximum system reliability and generate minimum possible losses. In addition tidal array topologies using this concept are developed. The final part of this thesis compares a number of different tidal array topologies based on resource to grid efficiency and component accessibility for maintenance. Results showed that when tidal current devices are clustered per four turbines on offshore platforms it is efficient to use as many clusters as possible connected to a single cable whose both ends are connected to the grid. Locating the power converters in the nacelle yields fewer electrical losses compared to locating the power converters on the offshore platform. However, the difference is minimised because the distance between the tidal current device and the offshore platform is the least possible. Having the power converters on an offshore platform is beneficial in terms of accessibility for maintenance and operation because they are not underwater. The results and the methodology from this thesis can be extended to other offshore renewable energy systems such as the wind and wave. In addition, this study can be used as a stepping stone for decision making by tidal current developers.
7

Propostas de procedimentos para projetar filtros harmônicos a partir de um programa de penetração harmônica, incluindo cálculos de desempenho e de suportabilidade

Nascimento, Rogério Pinto do 10 May 2007 (has links)
Conselho Nacional de Desenvolvimento Científico e Tecnológico / This work introduces some proposals for the design of harmonic filters from a harmonic penetration computer program. Such procedures are developed by means of optimized techniques, taking in account, among other aspects, the filtering performance, the filter detuning as well as international guides referring to the supportability of the filter components, as far as voltage, current and power are concerned. The work shows the need for designing filters through a harmonic penetration program. Therefore, the filter parameters can be calculated not only from harmonic currents driven from a single harmonic source (as usually it is made), but also from other existing (and unwanted) harmonic sources eventually present in the system, which could eventually be attracted by the harmonic filter. The work also introduces some studies of cases, in which single tuned filters are compared to damped filter. This study is made in a typical industrial plant, where an arc furnace (that produces characteristic and non-characteristic harmonic) is present. The study shows, among other aspects that, depending on some important requirements made in the design of the filters, a damped filter arrangement can be more advantageous than a single tuned one. / Este trabalho propõe diretrizes para a elaboração de procedimentos sistemáticos que conduzem ao projeto de filtros harmônicos, a partir de um programa de fluxo harmônico. Tais procedimentos são desenvolvidos por meio de técnicas otimizadas, levando-se em conta, dentre outros aspectos, o desempenho de filtragem, a dessintonia dos filtros, bem como normas referentes à suportabilidade dos componentes frente às grandezas elétricas do sistema. A elaboração de um projeto de filtros a partir de um programa de fluxo harmônico foi introduzida com o intuito de se determinar os filtros não somente a partir das correntes harmônicas oriundas de uma determinada carga harmônica (como usualmente é feito), mas também para outras fontes harmônicas porventura existentes no sistema e que, eventualmente, poderão ser indesejavelmente (porém, inevitavelmente) atraídas pelo filtro harmônico. O trabalho também apresenta alguns estudos de casos, nos quais há a comparação de desempenho entre filtros sintonizados e amortecidos. Neste sentido, o trabalho usa o programa digital desenvolvido para apresentar uma análise sobre o uso de filtros sintonizados ou amortecidos, em uma instalação industrial típica de usinas siderúrgicas, que produz correntes harmônicas de ordens não-características, inclusive. Nesse tocante, este estudo de casos mostra, dentre outros aspectos, que, dependendo de certas considerações feitas no projeto dos filtros sintonizados, estes podem até dispensar somas de potência reativa maiores do que os filtros amortecidos. / Mestre em Ciências
8

Planejamento integrado de filtros harmônicos e reguladores de tensão em sistemas de distribuição utilizando um algoritmo multiobjetivo / Integrated planning of harmonic filters and voltage regulators in distribution systems using a multiobjective algorithm

Santos, Felipe Santana 24 February 2017 (has links)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The increase in linear and non-linear loads experienced by Brazil in recent years has changed the way distribution networks are planned and Operated. In addition, the competitiveness of the market and the demand for the improvement in power quality indexes mean that current e orts are increasingly focused on areas such as voltage profile control and voltage harmonic distortion control. This work deals, exactly, with the Integrated control of voltage and harmonic voltage distortion (volt/thd) in distribution systems, within the scope of planning, through the insertion of passive harmonics filters and voltage regulators. To solve the problem in question, a multiobjective algorithm, the NSGA-II, is applied, since the presented problem can be treated as a combinatorial optimization problem. The power summation method is used as an alternative for the resolution of the load flow. While the current injection method is used as a calculation of the harmonic flow. The mathematical models of the network components were presented, taking into account the influence of frequency, in a detailed way. The proposed algorithm was applied in benchmark systems, a 34-bus and a 104-bus, the systems were simulated with and without the presence of the devices for comparison and validation of the results. / O aumento de cargas, lineares e não-lineares, vivenciado pelo Brasil nos últimos anos, tem alterado a maneira com as redes de distribuição são planejadas e operadas. Além disso, a competitividade do mercado e exigência pela melhoria nos índices de qualidade da energia fazem com que os esforços atuais sejam cada vez mais direcionados para áreas como o controle do perfil de tensão e o controle das distorções harmônicas de tensão. Esta dissertação trata, exatamente, do controle integrado de tensão e distorção harmônica de tensão (volt/dht) em sistemas de distribuição, no âmbito do planejamento, através da inserção de filtros harmônicos passivos e reguladores de tensão. Para resolver o problema em questão, um algoritmo multiobjetivo, o NSGA-II, é aplicado, uma vez que o problema apresentado é tratado como um problema de otimização combinatória. O método da soma de potências é utilizado como alternativa para a resolução do fluxo de carga. Enquanto que o método da injeção de correntes é utilizado como cálculo do fluxo de harmônicos. Os modelos matemáticos dos componentes da rede foram apresentados, levando-se em consideração a influência da frequência, de forma detalhada. O algoritmo proposto foi aplicado em sistemas teste de 34 e 104 barras e os sistemas foram simulados com e sem a presença dos dispositivos para efeito de comparação e validação dos resultados.
9

An Impact Study of DC Protection Techniques for Shipboard Power Systems

Hamilton, Hymiar 11 August 2007 (has links)
The need for DC power at continuous uninterrupted rates is a reality for ship survival during highly intense combat and regular travel. The new proposed distribution system on the all-electric ship is designed using a DC distribution method (zones) in which the use of transformers and frequency issues/manipulation can be eliminated with the use of power electronics. These power electronic devices can greatly simplify the system and provide more available space, possible cost reduction, and variable control. One key feature is to make sure that the DC buses/systems and converters/rectifiers are protected from faults, transients, and other malicious events that can cause unwanted interference, shutdown, and possible damage or destruction. DC faults can have a detrimental impact on the ship performance. DC protection should allow for high speed and highly sensitive detection of faults enhancing reliability in the supply of electric power. DC fault protection geared towards a lower voltage scenario/system has not yet been studied and analyzed rigorously. The research goal of this work has been to develop a method in which the system can detect a DC fault and perform suppression of the fault and return to normal operating conditions once the fault is removed. The use of power electronics and DC fault detection methods are employed to determine how to best protect the system?s stability and longevity. The findings of the research work have demonstrated that using zero-crossing logic on the AC side of the system is beneficial in DC fault detection. Also, different grounding schemes can produce different effects, whereas some grounding schemes can help protect the system during a disturbance.

Page generated in 0.0998 seconds