Στις μέρες μας το ενεργειακό πρόβλημα αποτελεί ένα από τα σπουδαιότερα προβλήματα του πλανήτη, το οποίο μαζί με την ραγδαία κλιματική αλλαγή οδηγούν στην ανάγκη για παραγωγή ηλεκτρικής ενέργειας με όσο πιο οικονομικό αλλά και φιλικό προς το περιβάλλον τρόπο. Συνεπώς οι Ανανεώσιμες Πηγές Ενέργειας και κυρίως η αιολική ενέργεια αποκτούν σπουδαίο ρόλο στο στόχο αυτό και αλλάζουν άρδην τόσο τον Ευρωπαϊκό όσο και τον Παγκόσμιο ενεργειακό χάρτη. Στην παρούσα διπλωματική εργασία μελετάμε μια διάταξη ανεμογεννήτριας, η οποία αποτελείται σε πρώτη φάση από μια επαγωγική μηχανή βραχυκυκλωμένου κλωβού (SCIG), από έναν μετατροπέα συχνότητας (back-to-back converter) και από ένα σε σειρά συνδεδεμένο τριφασικό R-L φίλτρο στην ac πλευρά μέχρι το ζυγό διασύνδεσης με το δίκτυο, ενώ στη συνέχεια προσθέτουμε, μετά το R-L φίλτρο, μια συστοιχία πυκνωτών συνδεδεμένων σε αστέρα, ένα τριφασικό R-L φορτίο στο ίδιο σημείο με τη συστοιχία πυκνωτών καθώς και τη γραμμή μεταφοράς για σύνδεση με το δίκτυο. Σκοπός λοιπόν αυτής της εργασίας είναι να μελετήσουμε το πλήρες σύστημα της ανεμογεννήτριας στο d-q στρεφόμενο σύστημα κάθετων αξόνων μέσω του μετασχηματισμού Park. Στη συνέχεια προχωρούμε στον υπολογισμό των εξισώσεων στο χώρο κατάστασης και τελικά προτείνουμε ένα σύστημα ελέγχου το οποίο βασίζεται στους PI ελεγκτές. Τέλος, προσομοιώνουμε το πλήρες σύστημα με το Simulink του MATLAB και στη συνέχεια παρουσιάζουμε τις αποκρίσεις των προσομοιώσεων και εξάγουμε συμπεράσματα. / Nowadays the energy problem is one of the most important global problems, which together with the rapid climate change lead to the need for power generation as more economical and environmentally friendly way. Therefore, the Renewable Energy Sources and especially wind power have a great role in this objective and radically change both the European and the global energy map. In this paper we study a wind turbine device, which consists at first of a squirrel cage induction generators (SCIG), a frequency converter (back-to-back converter) and an three-phase R-L filter on the grid side and then me add, after the filter, a capacitor bank connected in star, a three-phase R-L load at the same point with the capacitor banks and the transmission line for grid connection. Aim of this thesis is to study the complete wind turbine system in the d-q rotating vertical axes system through the Park transformation. Then we proceed to the calculation of the equations in state space and eventually propose a control system based on PI controllers. Finally, we simulate the complete system with the MATLAB/Simulink and then we present simulations of the responses and draw conclusions.

Recent failures of large induction machines due to rotor bar breaks have become a major industrial concern in South Africa. These failures have occurred while applying current condition monitoring methods. This would imply that current theories are either inadequate or badly implemented. This thesis investigates two currently used condition monitoring strategies which focus on monitoring the stator current and axial vibration to detect bar breaks as well as a third method which involves putting destructive shaft voltages to good use and using this signal to diagnose rotor defects. This document begins by familiarizing the reader with two conventional approaches which involve monitoring the stator current and the axial vibration to detect rotor bar breaks. Thereafter the origins of shaft voltage are discussed and its use as a condition monitoring tool is first theoretically derived and then validated by finite element simulations. A thorough discussion of the measurement equipment required is presented and ultimately the performance of these three methods is tested by means of a laboratory measurement as well as two on-site measurements. The results from these measurements suggest that when making proper use of both conventional condition monitoring methods, these methods have a 50% success rate in the detection of rotor bar breaks. The alternative method investigated, which involves monitoring the shaft voltage, has a 75% success rate in the detection of rotor bar breaks. This highlights the use of shaft voltage as a condition monitoring tool. / Dr. S. R. Holm Prof. W. A. Cronje

<p> The speed of a squirrel-cage induction motor is controlled by varying the supply frequency. The design of an SCH controlled inverter, using gating from a logic unit to give a variable-frequency power-level output, is described.</p> / Thesis / Master of Engineering (MEngr)

Ένα από τα σύγχρονα προβλήματα που απασχολούν του την κοινωνία είναι το ενεργειακό πρόβλημα, απόρροια της σταδιακής εξάντλησης των συμβατικών πηγών ενέργειας. Μία ιδιαίτερα ελκυστική λύση, αποτελεί η αξιοποίηση των ανανεώσιμων πηγών ενέργειας και ειδικά του ανέμου που παρέχει την αιολική ενέργεια. Η παρούσα διπλωματική εργασία έχει ως θέμα τον έλεγχο ανεμογεννήτριας επαγωγικής μηχανής βραχυκυκλωμένου κλωβού(SCIG) με χρήση ασαφούς λογικής. Ο έλεγχος με ασαφή λογική είναι ταχέως αναπτυσσόμενος καθώς πλησιάζει πολύ στην ανθρώπινη λογική. Βασιστήκαμε πάνω σε ένα ήδη υπάρχον μοντέλο μη-γραμμικού ελέγχου για αυτό το είδος ανεμογεννήτριας και το μετατρέψαμε κατάλληλα για την σταδιακή εφαρμογή της ασαφούς λογικής. Το σύστημα προσομοιώθηκε με τη βοήθεια της εφαρμογής Simulink του λογισμικού Matlab. Τα αποτελέσματα παρουσιάζονται μέσω διαγραμμάτων και εξάγονται τα ανάλογα συμπεράσματα. / One of the current issues that concern the society is the energy problem of the gradual depletion of conventional energy sources. A particularly attractive solution is the exploitation of renewable energy sources, especially wind providing the wind. This thesis will deal with controlling wind turbine induction motor squirrel cage (SCIG) using fuzzy logic. The control with fuzzy logic is rapidly growing as it approaches the human sense. We relied on an existing model of nonlinear control for this type turbine and turned it suitable for the application of fuzzy logic. The system was simulated with the help of application Simulink software Matlab. The results are presented through diagrams and the relative conclusions are extracted.

Thesis (Ph. D.), Memorial University of Newfoundland, 1999. / Bibliography: p. 179-186.

Thesis (M.S.)--Cleveland State University, 2010. / Abstract. Title from PDF t.p. (viewed on June 3, 2010). Includes bibliographical references (p. 118-120). Available online via the OhioLINK ETD Center and also available in print.

Dentre as fontes de energia renováveis utilizadas para geração de energia elétrica a que mais se destaca atualmente e a energia eólica. 0 crescente índice de penetração da geração eólica na matriz energética dos sistemas de potencia impõe a necessidade da revisão de conceitos anteriormente estabelecidos sobre a estabilidade de sistemas de potencia, uma vez que ainda não e perfeitamente compreendida a influencia de uma maior integração deste recurso no comportamento dos sistemas de potencia. Este trabalho tem como foco o estudo da estabilidade de sistemas com aerogeradores de velocidade fixa equipados com geradores de indução de rotor em gaiola. E estudada a estabilidade angular de um sistema de geração eólica equipado com aerogeradores desta natureza. O problema da estabilidade foi decomposto em três partes: estabilidade estática, estabilidade dinâmica e estabilidade transitória. São definidos os modelos dos componentes do aerogerador para cada um dos estudos realizados. A topologia adotada á a máquina Barramento Infinito (MBI), na qual o restante do sistema de potência a representado pelo seu equivalente de Thevenin. Esta topologia típica de analise de estabilidade de sistemas de potencia e adotada por permitir a obtenção de resultados analíticos para as analises estática e dinâmica. A analise transitória se dá através de simulações computacionais. A fim de manter um caráter mais geral para os resultados as simulações são realizados com três aerogeradores de características distintas. Os resultados obtidos permitem uma melhor compreensão da influencia sobre a estabilidade do sistema de geração eólica dos parâmetros de rede do sistema de potencia como: potencia de curto-circuito do ponto de conexão comum com o sistema de potencia, relação X/R da linha de transmissão e do capacitor de compensação de fator de potencia. / Among the renewable energy sources used to generate electric power one of the most important at this time is the wind power. The growing penetration index of wind power in the power systems energetic matrix leads to the necessity of a reevaluation of the concepts previously established about the stability of power systems, since the influence of a major integration of this resource in the behavior of power systems is not perfectly understood. This work focuses on the stability study of wind power systems equiped with fixed-speed squirrel-cage induction generators. The angular stability of a wind generation system equipped with wind generators of this nature is studied. The stability problem was decomposed in three parts: static stability, dynamic stability and transient stability. The models of the components of the wind generator are defined for each of the studies. The considered topology was an Induction Generator Infinite Bus System (IBM), where the rest of the power system is represented by it’s Thévenin equivalent. This is a typical topology in power systems stability analysis and is adopted in this work aiming at obtaining analytical and general stability results. The transient analysis is performed by computer simulations. In order to provide more generatily to the stability results, all simulations are conducted with three wind generators with distinct characteristics. The obtained results allow a better comprehension about the influence, on the stability of wind power systems, of power system network parameters as: short-circuit capacity of the common connection point with the power system, the X/R relation of the transmission line and the power factor compensation capacitor.

Dentre as fontes de energia renováveis utilizadas para geração de energia elétrica a que mais se destaca atualmente e a energia eólica. 0 crescente índice de penetração da geração eólica na matriz energética dos sistemas de potencia impõe a necessidade da revisão de conceitos anteriormente estabelecidos sobre a estabilidade de sistemas de potencia, uma vez que ainda não e perfeitamente compreendida a influencia de uma maior integração deste recurso no comportamento dos sistemas de potencia. Este trabalho tem como foco o estudo da estabilidade de sistemas com aerogeradores de velocidade fixa equipados com geradores de indução de rotor em gaiola. E estudada a estabilidade angular de um sistema de geração eólica equipado com aerogeradores desta natureza. O problema da estabilidade foi decomposto em três partes: estabilidade estática, estabilidade dinâmica e estabilidade transitória. São definidos os modelos dos componentes do aerogerador para cada um dos estudos realizados. A topologia adotada á a máquina Barramento Infinito (MBI), na qual o restante do sistema de potência a representado pelo seu equivalente de Thevenin. Esta topologia típica de analise de estabilidade de sistemas de potencia e adotada por permitir a obtenção de resultados analíticos para as analises estática e dinâmica. A analise transitória se dá através de simulações computacionais. A fim de manter um caráter mais geral para os resultados as simulações são realizados com três aerogeradores de características distintas. Os resultados obtidos permitem uma melhor compreensão da influencia sobre a estabilidade do sistema de geração eólica dos parâmetros de rede do sistema de potencia como: potencia de curto-circuito do ponto de conexão comum com o sistema de potencia, relação X/R da linha de transmissão e do capacitor de compensação de fator de potencia. / Among the renewable energy sources used to generate electric power one of the most important at this time is the wind power. The growing penetration index of wind power in the power systems energetic matrix leads to the necessity of a reevaluation of the concepts previously established about the stability of power systems, since the influence of a major integration of this resource in the behavior of power systems is not perfectly understood. This work focuses on the stability study of wind power systems equiped with fixed-speed squirrel-cage induction generators. The angular stability of a wind generation system equipped with wind generators of this nature is studied. The stability problem was decomposed in three parts: static stability, dynamic stability and transient stability. The models of the components of the wind generator are defined for each of the studies. The considered topology was an Induction Generator Infinite Bus System (IBM), where the rest of the power system is represented by it’s Thévenin equivalent. This is a typical topology in power systems stability analysis and is adopted in this work aiming at obtaining analytical and general stability results. The transient analysis is performed by computer simulations. In order to provide more generatily to the stability results, all simulations are conducted with three wind generators with distinct characteristics. The obtained results allow a better comprehension about the influence, on the stability of wind power systems, of power system network parameters as: short-circuit capacity of the common connection point with the power system, the X/R relation of the transmission line and the power factor compensation capacitor.

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2017. / Globally governments are faced with challenges in the energy sector which are exacerbated by uncertain financial markets and resource limitations. The over utilization of fossil fuels for electricity generation has had a profound impact on the climatic conditions on earth. Coal power stations release carbon dioxide (CO2) during the combustion process and studies show that concentrations have sharply risen in the atmosphere. Adverse environmental conditions like global warming exist as a result of high greenhouse gas (GHG) emissions in particular CO2. In 2015 Eskom constructed Sere Wind farm with a supply capability of 100 MW. Due to the lack of technical expertise and skills with regard to the new technology within Eskom, Siemens was offered a 5 year maintenance contract. Siemens also provides training on basic operation and maintenance (O&M) of the wind farm to Eskom staff. This excludes specialised training on Siemens Turbine Condition Monitoring (TCM) systems which is a critical part to develop optimum maintenance strategies. This shortage of specialised skills in the application of condition monitoring techniques within Eskom is a major concern. If the most cost effective maintenance strategies during the contract period are implemented, the long term plant health and design life of Sere wind farm will be reduced. There is a need to develop new condition monitoring techniques to complement or address the shortcomings of the existing systems. Developing these skills will increase the understanding of the technology and improve the operating and maintenance of Sere wind farm.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / Fixed speed wind turbines completely dominated the market until the mid-1990s and currently. Although most installed wind turbine are variable speed, many fixed speed wind are still in operation. In this context, this work presents a study concerned to coordinated operation of FACTS (Flexible Alternating Current Transmission Systems) device with fixed speed wind energy conversion system (WECS) equipped with a squirrel cage induction generator. The applied FACTS device is based on the control strategy of the Unified Conditioner Power Quality with inverted topology (i-UPQC), and consists of two static converters connected in back-to-back topology. A model was developed in the software PSCAD/EMTDC, tested under four different scenarios and discussed in order to validate the presented theory. The i-UPQC performance was analyzed for improving voltage quality in the point of common coupling (PCC), reduction of the harmonic currents drained from the wind turbine, and increasing the induction generator capacity to remain connected during a momentary collapse in the grid voltage. The i-UPQC presented good performance due to its capability to warrant the quality in the PCC voltage in spite of the wind variation and that the voltage sags at the PCC do not change the stator voltages. About the generator current, the i-UPQC has kept the stator current free of harmonic components and the effect of unbalanced loads. Under normal operation it was demonstrated that one of the I-UPQC converters can be sized as 50\% of the generator rated power, which is an advantage for real implementation. A comparison between two ways to connect the I-UPQC to the grid, along with the wind turbine, was made. The series converter connected between the wind turbine and the parallel converter, or between parallel converter and the common connection point (PCC). It was concluded that the shunt converter connected to the generator presents better performance than the series converter due to series converter currents are less than the stator currents. Under this configuration, there is no active power current from the generator injected in the PCC during voltage sags. / Turbinas de velocidade fixa dominaram completamente o mercado atà meados de 1990 e atualmente, apesar da maioria dos aerogeradores instalados serem de velocidade variÃvel, muitos aerogeradores de velocidade fixa ainda se encontram em funcionamento. Neste contexto, este trabalho apresenta um estudo sobre a operaÃÃo coordenada de um dispositivo FACTS (Flexible Alternating Current Transmission Systems) com um aerogerador de velocidade fixa, equipado com gerador de induÃÃo gaiola de esquilo. O dispositivo FACTS aplicado baseia-se na estratÃgia de controle do Condicionador Unificado de Qualidade de Energia com topologia invertida (i-UPQC, do inglÃs, Unified Power Quality Conditioner with inverted topology), e consiste de dois conversores estÃticos na configuraÃÃo back-to-back. Um modelo foi desenvolvido no software PSCAD/EMTDC e quatro cenÃrios diferentes foram simulados e discutidos a fim de validar a teoria apresentada. A partir dos resultados de simulaÃÃo, foi analisado o desempenho do i-UPQC para melhoria da qualidade da tensÃo no Ponto de ConexÃo Comum (PCC), diminuiÃÃo das correntes harmÃnicas drenadas do aerogerador e aumento da capacidade do gerador de induÃÃo de se manter conectado durante um afundamento momentÃneo da tensÃo da rede. O i-UPQC atuou de forma satisfatÃria, pois nÃo permitiu que variaÃÃes na velocidade do vento afetassem a qualidade da tensÃo fornecida ao PCC, nem que o afundamento da tensÃo no PCC alterasse a tensÃo nos terminais do estator. Quando cargas nÃo lineares foram adicionadas no sistema, o i-UPQC manteve a corrente do estator livre das componentes harmÃnicas e desbalanÃos presentes na corrente da carga. Demonstrou-se que, em condiÃÃes normais de operaÃÃo, um dos conversores do i-UPQC pode ser especificado para 50\% da potÃncia nominal do aerogerador, o que pode representar uma vantagem do i-UPQC para o caso de uma implementaÃÃo real. Foi feita uma comparaÃÃo entre duas diferentes configuraÃÃes de conexÃo do i-UPQC com o aerogerador e a rede: ora com o conversor paralelo conectado entre o conversor sÃrie e o ponto de conexÃo comum (PCC), ora conectado entre o aerogerador e o conversor sÃrie. Concluiu-se que a configuraÃÃo com o conversor paralelo conectado ao aerogerador à mais vantajosa, pois a corrente que circula atravÃs do conversor sÃrie à menor que a corrente do estator. Nesta configuraÃÃo, nenhuma corrente referente à potÃncia ativa do aerogerador à injetada no PCC durante um afundamento de tensÃo.