Thesis (M.S.)--Ohio University, August, 1996. / Title from PDF t.p.

Thesis (M.S.)--Oregon State University, 2004. / Printout. Includes bibliographical references (leaves 39-40). Also available on the World Wide Web.

Thesis (M.S.)--Michigan State University. Electrical Engineering, 2008. / Title from PDF t.p. (viewed on Aug. 5, 2009) Includes bibliographical references (p. 230-231). Also issued in print.

Σκοπός της διπλωματικής αυτής εργασίας είναι ο σχεδιασμός των μονάδων που αποτελούν ένα φωτοβολταϊκό σύστημα συνδεδεμένο στο δίκτυο χαμηλής τάσης καθώς και η εξομοίωση του συστήματος αυτού χρησιμοποιώντας ως εργαλείο το πρόγραμμα MATLAB/Simulink. Το πρώτο βασικότερο στοιχείο του συστήματος είναι η φωτοβολταϊκή γεννήτρια. Αναλύεται διεξοδικά η λειτουργία της μέσα από τη θεωρία, και ο σχεδιασμός της μέσα από μια σειρά υπολογισμών των σε σειρά και παράλληλων κλάδων κυττάρων που την αποτελούν. Η δημιουργία του μοντέλου της στο Simulink περιγράφεται λεπτομερώς και η ορθή λειτουργία της επιβεβαιώνεται από τις κυματομορφές εξόδου του μοντέλου αυτού. Το δεύτερο βασικό στοιχείο που επίσης αναλύεται διεξοδικά τόσο μέσω της θεωρίας όσο και μέσω της δημιουργίας του μοντέλου του στο πρόγραμμα, είναι ο μονοφασικός αντιστροφέας. Το σύστημα περιλαμβάνει επίσης τον dc πυκνωτή στην είσοδο του αντιστροφέα το παθητικό φίλτρο L-C στην έξοδο αυτού και πριν την σύνδεση με το δίκτυο χαμηλής τάσης, ένα φορτίο R-L. Μετά την ολοκλήρωση της θεωρητικής ανάλυσης του σχεδιασμού και της δημιουργίας των μοντέλων εξομοίωσης των επιμέρους στοιχείων του συστήματος, διερευνάται η λειτουργία του στην μόνιμη κατάσταση όπου απεικονίζονται οι κυματομορφές τάσεων και ρευμάτων σε διάφορα σημεία του συστήματος καθώς και το αρμονικό περιεχόμενό τους. Ο στόχος ήταν η φωτοβολταϊκή γεννήτρια να παράγει την μέγιστη δυνατή ισχύ, δηλαδή η dc τάση στα άκρα του πυκνωτή (τάση στην είσοδο του αντιστροφέα), να αντιστοιχεί σ’ αυτήν του σημείου μέγιστης ισχύος, χωρίς το αρμονικό περιεχόμενο των τάσεων και των ρευμάτων εξόδου να ξεπερνά τα επιτρεπτά όρια. / The purpose of this thesis is to design all units that constitute a photovoltaic system connected to low voltage grid, and also to run the simulation of this system using the program MATLAB/ Simulink. The first key element is the photovoltaic generator whose operation is discussed in detail through theory. In addition, the design of the photovoltaic generator takes place through calculations of the series and the parallel branches of cells that constitute it. The model of the generator is created in Simulink and its correct operation is confirmed by the characteristic waveforms of the model. The second key factor, which is also analyzed in greater length both through theory and through the creation of the model in the program, is the single-phase inverter. Moreover, the system includes a dc capacitor connected at the input of the inverter, a passive LC filter at the output of the same and an RL load, before the whole system is connected to the grid. After the theoretical analysis, the design and creation of simulation models of every component individually, the complete photovoltaic system is simulated in order to investigate its function in the steady state. During simulation voltages and currents in different parts of the system are measured, and their harmonic content is graphed. The goal was the photovoltaic generator to produce the maximum power, which means that the dc voltage across the capacitor (input voltage of the inverter) should correspond to that of the maximum power point, without the harmonic content of voltages and output currents to exceed the allowable limits.

Thesis (MScEng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: The three-level neutral-point-clamped(NPC) converter, being a widely used multilevel inverter, received a lot of attention recently due to problems associated with de-link capacitor voltage balancing. There are mainly two problems associated with the neutralpoint voltage of the NPC inverter: 1. At high modulation indices a low frequency ripple occurs on the neutral-point voltage. 2. Steady-state unbalance in the neutral-point voltage may arise due to a variety of factors including component imperfections, transients and other non-idealities and imbalances. In this thesis we study the balancing problem with focus on the steady-state imbalance. This is achieved by a systematic and mathematically rigorous study of the natural balancing mechanisms of the three-level three-phase NPC inverter. Orthogonality of two sets of switching spectra in the frequency domain would imply that the DC-bus voltages balance in the steady state. This is done through mathematical analysis using Carrara's PWM strategy of alternative phase opposition disposition(APOD), phase opposition disposition( POD) and phase disposition(PD); and Bennet's geometric model for double Fourier series adapted for use with power converter systems by Bowes. The theory is verified through simulation. / AFRIKAANSE OPSOMMING: Aangesien die drie-vlak, geklemde, neutrale-punt omsetter(NPC) 'n algemene omsetter konfigurasie is, is daar onlangs baie aandag gegee aan die probleme wat geassosieer word met die balansering van die omsetter se gelykstroombuskapasitorspanning. Die twee hoof probleme wat gepaart gaan met die neutraalpuntspanning van die NPC omsetter is: 1. Met 'n ho modulasie-indeks ontstaan daar 'n lae frekwensie rippel op die neutralepuntspanning. 2. 'n Bestendige toestand wanbalans van die neutrale-puntspanning kan ontstaan as gevolg van 'n verskeidenheid faktore, onder andere komponent nie-idealiteite, oorgangs- en ander wanbalanse. In hierdie tesis word op die bestendige-toestandwanbalans gefokus. Dit word gedoen deur middel van die neutraalbalanseeringsmeganisme van die drie-vlak, drie-fase NPC omsetter, sistematies en gedetaileerd wiskundig te bestudeer. In die bestendige toestand sal orgonaliteit van twee stelle skakel spektras in die frekwensie gebied, GS-bus spanning balans impliseer. Dit word wiskundig geanaliseer deur gebruik te maak van Carrara se alternatiewe fase opposiesie disposisie (APOD), fase oposisie disposisie (POD) en fase disposisie(PD), puls-wydte modulasie strategie, asook Bennet se geometriese modelle vir die dubbel Fourier reeks wat aangepas is vir drywingsomsetters deur Bowes. Ten slotte is die teorie geverifieer deur simulasies.

Made available in DSpace on 2014-06-11T19:30:51Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-06-25Bitstream added on 2014-06-13T20:40:37Z : No. of bitstreams: 1 brito_mag_dr_ilha.pdf: 5064752 bytes, checksum: 82cb4f68cac0b9124f16164ae4f2e99d (MD5) / Esta proposta de tese se baseia na necessidade atual e tendência mundial na busca por sistemas cada vez mais eficientes e que se baseiem em fontes de energia alternativas menos poluentes, renováveis e que produzam pouco impacto ambiental. Desta forma, são desenvolvidos sistemas de geração de energia elétrica de pequeno porte baseado em painéis solares fotovoltaicos. Com o intuito de aumentar o rendimento e a densidade de potência dos sistemas, são apresentadas novas estruturas de inversores monofásicos e trifásicos integrados para aplicação como sistemas isolados e/ou conectados à rede de distribuição em corrente alternada (CA), operando como sistemas de geração distribuídos. Os inversores integrados são apresentados com o intuito de substituir os usuais sistemas de conversão de energia a duplo estágio. Incorporado aos inversores integrados são implementados métodos e dispositivos para extração da máxima potência possível dos painéis fotovoltaicos (algoritmo de MPPT), aumentando assim o aproveitamento de energia advinda destes painéis. Além disso, em virtude da necessidade de conexão segura destes sistemas à rede de distribuição de energia elétrica em corrente alternada, são realizadas análises e a implementação de métodos de sincronismo com a rede de CA em baixa tensão; além da análise e síntese de métodos híbridos para detecção e gestão do efeito de ilhamento, a fim de garantir a segurança do sistema. O controle dos conversores e as técnicas de MPPT, gestão e detecção de ilhamento, bem como de sincronismo com a rede em CA são implementadas de forma digital, com o objetivo de propiciar maior flexibilidade na concepção das lógicas de controle adequadas às aplicações propostas. Finalmente, destaca-se que o trabalho trouxe contribuições significativas para a melhoria na implementação... / This work is based on the actual necessity and world tendency for high-efficiency systems based on renewable energy sources which are less pollutant and produces little environmental impact, and, for this purpose, it is developed some photovoltaic electrical generation systems to operate as a small distribution generation system (DG). With the purpose to increase efficiency and power density, new single-phase and three-phase integrated inverter topologies are presented for operating as stand-alone and/or grid-connected systems. The main idea of these inverters is the replacement of the conventional two-stage cascaded solutions. Main maximum power point tracking techniques are implemented and tested in order to increase energy utilization. Furthermore, because of safe-operation grid connection necessities this work presents analysis and implementation of active and hybrid anti-island detection techniques and synchronization methods with the AC low voltage grid. The converters control system and MPPT techniques, anti-island detection and management system together with the synchronization are implemented digitally, with the purpose of increasing flexibility for the overall control circuitry. Finally, this work has presented significant contributions regarding the P&O and IC based on PI MPPT techniques and has presented the integration procedures in order to obtain new families of single and three-phase inverters. Moreover, this is the first thesis that has presented the tri-state three-phase inverters injecting power into the grid. These inverters have inovations at its control and modulation that permit the input to... (Complete abstract click electronic access below)

CAPES / Este trabalho apresenta o estudo, projeto e implementação digital usando DSP de um Filtro Ativo de Potência Paralelo (FAPP) trifásico com potência de 4,5kVA, sendo este implementado utilizando três topologias de inversores monofásicos em ponte completa compartilhando o mesmo barramento de tensão CC. O FAPP é utilizado em sistemas trifásicos a quatro-fios para supressão de harmônicos de corrente, compensação de reativos e compensação de desbalanços das correntes de carga. Dentre as características mais relevantes desta topolgia de FAPP, pode-se citar: possibilidade de controle de corrente independente entre as fases; tensão reduzida no barramento CC; isolação galvânica entre o FAPP e a rede elétrica; e modularidade. Os algoritmos adotados para obtenção das correntes de referência de compensação são fundamentados no método de controle baseado no sistema de eixos de referência síncrona (SRF). Estes podem ser empregados em sistemas monofásicos bastando, para isso, a criação de um sistema trifásico fictício. Desse modo, em um sistema trifásico a quatro-fios, cada uma das correntes de fase pode ser controlada de forma independente. Duas estratégias distintas de operação do FAPP são implementadas. Na primeira delas, chamada de Controle de Corrente Independente por Fase (CCIF), o FAPP atua na supressão de correntes harmônicas da carga e compensação de potência reativa. Neste caso, as correntes da rede serão senoidais, no entanto desequilibradas. Na segunda estratégia, além de atuar na supressão de harmônicas da carga e compensação de potência reativa, o FAPP também atua na Compensação dos Desequilíbrios das Correntes de Carga (CDCC). Assim, as correntes da rede, além de senoidais, serão equilibradas. Análises matemáticas são realizadas de forma a obter o modelo matemático que representa o sistema físico do FAPP. Além disso, é apresentada uma metodologia de projeto para a obtenção dos ganhos dos controladores das malhas de corrente e de tensão do barramento CC. Resultados de simulação e experimentais são apresentados de forma a validar o desenvolvimento teórico realizado e avaliar o desempenho do FAPP. / This work deals with the study, design and digital implementation by means of digital signal processor (DSP) of a 4.5kVA three-phase shunt active power filter (SAPF), which is implemented by using three single-phase full-bridge converters sharing the same dc-bus voltage. The SAPF is applied to three-phase four-wire systems performing harmonic current suppression, reactive power compensation and load unbalance compensation. The main characteristics of the SAPF topology can be related: possibility of independent current control; low DC-link voltage; galvanic isolation between the SAPF and the grid utility; and possibility of modular implementation. The algorithms adopted for obtaining the current references are based on the synchronous reference frame (SRF) control method. They can be employed in single-phase systems by creating a fictitious three-phase system. Thereby, in a three-phase four-wire system, it is possible the controlling of each phase current independently. Two different operation strategies of the SAPF are implemented. In the first one, which is called Independent Phase-Current Control (IPCC), the SAPF performs harmonic current suppression and reactive power compensation. In this case, the source current will become sinusoidal although unbalanced. In the second strategy, besides acting in the harmonic current suppression and reactive power compensation, the SAPF performs Load Unbalance Compensation (LUnC). In this case, the source currents will become sinusoidal and balanced. Mathematical analyses are carried out in order to obtain the mathematical model which represents the physical system of the SAPF. Additionally, a design methodology is presented, which is used to obtain the controller gains of both current and dc-bus voltage loops. Simulation and experimental results will be presented in order to validate the presented theoretical development and evaluate the performance of the SAPF.

CAPES / Este trabalho apresenta o estudo, projeto e implementação digital usando DSP de um Filtro Ativo de Potência Paralelo (FAPP) trifásico com potência de 4,5kVA, sendo este implementado utilizando três topologias de inversores monofásicos em ponte completa compartilhando o mesmo barramento de tensão CC. O FAPP é utilizado em sistemas trifásicos a quatro-fios para supressão de harmônicos de corrente, compensação de reativos e compensação de desbalanços das correntes de carga. Dentre as características mais relevantes desta topolgia de FAPP, pode-se citar: possibilidade de controle de corrente independente entre as fases; tensão reduzida no barramento CC; isolação galvânica entre o FAPP e a rede elétrica; e modularidade. Os algoritmos adotados para obtenção das correntes de referência de compensação são fundamentados no método de controle baseado no sistema de eixos de referência síncrona (SRF). Estes podem ser empregados em sistemas monofásicos bastando, para isso, a criação de um sistema trifásico fictício. Desse modo, em um sistema trifásico a quatro-fios, cada uma das correntes de fase pode ser controlada de forma independente. Duas estratégias distintas de operação do FAPP são implementadas. Na primeira delas, chamada de Controle de Corrente Independente por Fase (CCIF), o FAPP atua na supressão de correntes harmônicas da carga e compensação de potência reativa. Neste caso, as correntes da rede serão senoidais, no entanto desequilibradas. Na segunda estratégia, além de atuar na supressão de harmônicas da carga e compensação de potência reativa, o FAPP também atua na Compensação dos Desequilíbrios das Correntes de Carga (CDCC). Assim, as correntes da rede, além de senoidais, serão equilibradas. Análises matemáticas são realizadas de forma a obter o modelo matemático que representa o sistema físico do FAPP. Além disso, é apresentada uma metodologia de projeto para a obtenção dos ganhos dos controladores das malhas de corrente e de tensão do barramento CC. Resultados de simulação e experimentais são apresentados de forma a validar o desenvolvimento teórico realizado e avaliar o desempenho do FAPP. / This work deals with the study, design and digital implementation by means of digital signal processor (DSP) of a 4.5kVA three-phase shunt active power filter (SAPF), which is implemented by using three single-phase full-bridge converters sharing the same dc-bus voltage. The SAPF is applied to three-phase four-wire systems performing harmonic current suppression, reactive power compensation and load unbalance compensation. The main characteristics of the SAPF topology can be related: possibility of independent current control; low DC-link voltage; galvanic isolation between the SAPF and the grid utility; and possibility of modular implementation. The algorithms adopted for obtaining the current references are based on the synchronous reference frame (SRF) control method. They can be employed in single-phase systems by creating a fictitious three-phase system. Thereby, in a three-phase four-wire system, it is possible the controlling of each phase current independently. Two different operation strategies of the SAPF are implemented. In the first one, which is called Independent Phase-Current Control (IPCC), the SAPF performs harmonic current suppression and reactive power compensation. In this case, the source current will become sinusoidal although unbalanced. In the second strategy, besides acting in the harmonic current suppression and reactive power compensation, the SAPF performs Load Unbalance Compensation (LUnC). In this case, the source currents will become sinusoidal and balanced. Mathematical analyses are carried out in order to obtain the mathematical model which represents the physical system of the SAPF. Additionally, a design methodology is presented, which is used to obtain the controller gains of both current and dc-bus voltage loops. Simulation and experimental results will be presented in order to validate the presented theoretical development and evaluate the performance of the SAPF.

D.Ing. (Electrical and Electronic Engineering) / This thesis presents a series of analyses developed for several voltage source inverter topologies, which are indispensable in aiding the understanding and the design of these circuits. It describes the groundwork that is required for the development of custom design software for voltage source inverters. The different circuits that can be designed by using this program, are analyzed using conventional circuit analysis techniques. The equations are used to simulate the switching behaviour and to specify the required or recommended ratings of the main devices. The custom design program can be used to design three different topologies of voltage source inverters: a) hard switching (snubberless) six pulse bridge; b) hard switching (snubberless) six pulse bridge, equipped with a simple voltage clamp; and c) soft switching (snubbed) six pulse bridge, equipped with a conventional dissipative snubber circuit. The snubberless behaviour of a voltage source inverter leg is both experimentally and analytically investigated. Approximate equations are formulated which can be used to. determine the peak ratings of the main devices in the inverter, taking the reverse recovery of the freewheel diodes into account. The snubberless behaviour of an inverter leg, equipped with a simple voltage clamp across the dc link, is experimentally and theoretically investigated. Equations for design and determining the required peak ratings of the main devices are developed. It is shown that the simple voltage clamp can operate in two different modes, either as a fast discharging or as a slow discharging voltage clamp and that the ranges of applicability of thetwo modes of operation are different. Design rules for both modes of operation are presented. In order to develop the design equations for a snubbed inverter leg a suitable topology had to be identified first. A method for objectively comparing different inverter toplogies is proposed in this thesis, according to which the minimum on- and off-states of the main devices in the different topologies are compared for identical applications. This method is used to compare four different snubbed voltage source inverter topologies both theoretically and experimentally. As both methods indicate that the conventional snubber circuit allows the highest PWM switching frequency of the uncontrolled snubber circuits, this circuit is further investigated in its dissipative topology to develop the equations required for simulation and for inclusion in the program. The influence of snubber circuits on inductive inverter loads is also investigated. It is shown that for normal snubber sizes the effect of dead time forms the larger part of the output voltage distortion and that the effects of the snubber elements are normally of secondary importance. The effect of asymmetry of a specific snubber circuit on inverter loads is investigated and it is found that it introduces a de component in the output voltage. Finally the application of linear snubbers to switches that exhibit tail-forming characteristics is analyzed and optimized. The results allow the designer to minimize the total losses of the converter by identifying the optimal snubber size. The theoretical results are experimentally verified

This thesis presents methods for voltage management in distribution systems with high photovoltaic (PV) power production. The high PV penetration leads to both new challenges such as voltage profile violation and reverse power flow, and also new opportunities. Traditionally, the voltage control in the distribution network is achieved by common devices in the networks such as capacitor banks, static synchronous compensators (STATCOMs) and on-load tap changers (OLTCs). This thesis has considered existing reactive power capable solar PV inverters together with STATCOMs to provide voltage support for the distribution network. In this thesis, two effective coordination methods using the STATCOM and PV inverters are developed in order to study their interaction and how they together can stabilize the voltage level. Data from existing low-voltage (LV) and medium-voltage (MV) networks are used for a case study. The first control method is developed for LV network’s voltage control by means of PV inverter and STATCOM. The second control method is developed for both LV and MV networks’ voltage control, where reactive power control in PV inverters and STATCOMs are used in the LV network and only STATCOMs in the MV network. The control methods follow a hierarchical structure where reactive power compensation using PV inverters are prioritized. The STATCOMs, first in the LV and thereafter in the MV network in the second control method, are used only when the PV inverters are not able to provide or consume enough reactive power. This is beneficial due to the significant reduction in numbers of STATCOMs and their operation. The simulation results indicate that the proposed method is able to control both the over- and undervoltage situations for the test distribution networks. It is also shown that reactive power supply at night by the PV inverters can be an important resource for effective voltage regulation by using the proposed coordinated voltage control method.