Modern 'more-electric' aircraft demand increased levels of electrical power as non-propulsive power systems are replaced with electrical equivalents. This electrical power is provided by electrical generators, driven via a mechanical transmission system, from a rotating spool in the gas turbine core. A wide range of electrical loads exist throughout the aircraft, which may be pulsating and high powered, and this electrical power demand is transferred though the generators to produce a torque load on the drivetrain. The mechanical components of the drivetrain are designed for minimum mass and so are susceptible to fatigue, therefore the electrical loading existing on modern airframes may induce fatigue in key mechanical components and excite system resonances in both mechanical and electrical domains. This electro-mechanical interaction could lead to a reduced lifespan for mechanical components and electrical network instability.This project investigates electro-mechanical interaction in the electrical power offtake from large diameter aero gas turbines. High fidelity modelling of the drivetrain, and generator, allow the prediction of system resonances for a generic gas turbine-generator system. A Doubly-Fed Induction Generator (DFIG) is considered and modelled. DFIGs offer opportunities due to their fast dynamics and their ability to decouple electrical and mechanical frequencies (e.g. enabling a constant frequency electrical system with a variable speed mechanical drive). A test platform is produced which is representative of a large diameter gas turbine and reproduces the electro-mechanical system behaviour. The test platform is scaled with respect to speed and power but maintains realistic sizing between component dimensions which include: a gas turbine mechanical spool emulation, transmission driveshafts and gearbox, and accessory loads such as a generator. This test platform is used to validate theoretical understanding and suggest alternative mechanical configurations, and generator control schemes, for the mitigation of electro-mechanical interaction.The novel use of a DFIG and an understanding of electro-mechanical interaction allow future aircraft designs to benefit from the increased electrification of systems by ensuring that sufficient electrical power can be provided by a robust gas turbine-generator system.

No description available.

Indiana University-Purdue University Indianapolis (IUPUI) / In this research, a Split-Shaft Wind Energy Conversion System (SS-WECS) is investigated to improve the performance and cost of the system and reduce the wind power uncertainty influences on the power grid. This system utilizes a lightweight Hydraulic Transmission System (HTS) instead of the traditional gearbox and uses a Doubly-Fed Induction Generator (DFIG) instead of a synchronous generator. This type of wind turbine provides several benefits, including decoupling the shaft speed controls at the turbine and the generator. Hence, maintaining the generator’s frequency and seeking maximum power point can be accomplished independently. The frequency control relies on the mechanical torque adjustment on the hydraulic motor that is coupled with the generator. This research provides modeling of an SS-WECS to show its dependence on mechanical torque and a control technique to realize the mechanical torque adjustments utilizing a Doubly-Fed Induction Generator (DFIG). To this end, a vector control technique is employed, and the generator electrical torque is controlled to adjust the frequency while the wind turbine dynamics influence the system operation. The results demonstrate that the generator’s frequency is maintained under any wind speed experienced at the turbine. Next, to reduce the size of power converters required for controlling DFIG, this research introduces a control technique that allows achieving MPPT in a narrow window of generator speed in an SS-WECS. Consequently, the size of the power converters is reduced significantly. The proposed configuration is investigated by analytical calculations and simulations to demonstrate the reduced size of the converter and dynamic performance of the power generation. Furthermore, a new configuration is proposed to eliminate the Grid- Side Converter (GSC). This configuration employs only a reduced-size Rotor-Side Converter (RSC) in tandem with a supercapacitor. This is accomplished by employing the hydraulic transmission system (HTS) as a continuously variable and shaft decoupling transmission unit. In this configuration, the speed of the DFIG is controlled by the RSC to regulate the supercapacitor voltage without GSC. The proposed system is investigated and simulated in MATLAB Simulink at various wind speeds to validate the results. Next, to reduce the wind power uncertainty, this research introduces an SS-WECS where the system’s inertia is adjusted to store the energy. Accordingly, a flywheel is mechanically coupled with the rotor of the DFIG. Employing the HTS in such a configuration allows the turbine controller to track the point of maximum power (MPPT) while the generator controller can adjust the generator speed. As a result, the flywheel, which is directly connected to the shaft of the generator, can be charged and discharged by controlling the generator speed. In this process, the flywheel energy can be used to modify the electric power generation of the generator on-demand. This improves the quality of injected power to the grid. Furthermore, the structure of the flywheel energy storage is simplified by removing its dedicated motor/generator and the power electronics driver. Two separate supervisory controllers are developed using fuzzy logic regulators to generate a real-time output power reference. Furthermore, small-signal models are developed to analyze and improve the MPPT controller. Extensive simulation results demonstrate the feasibility of such a system and its improved quality of power generation. Next, an integrated Hybrid Energy Storage System (HESS) is developed to support the new DFIG excitation system in the SS-WECS. The goal is to improve the power quality while significantly reducing the generator excitation power rating and component counts. Therefore, the rotor excitation circuit is modified to add the storage to its DC link directly. In this configuration, the output power fluctuation is attenuated solely by utilizing the RSC, making it self-sufficient from the grid connection. The storage characteristics are identified based on several system design parameters, including the system inertia, inverter capacity, and energy storage capacity. The obtained power generation characteristics suggest an energy storage system as a mix of fast-acting types and a high energy capacity with moderate acting time. Then, a feedback controller is designed to maintain the charge in the storage within the required limits. Additionally, an adaptive model-predictive controller is developed to reduce power generation fluctuations. The proposed system is investigated and simulated in MATLAB Simulink at various wind speeds to validate the results and demonstrate the system’s dynamic performance. It is shown that the system’s inertia is critical to damping the high-frequency oscillations of the wind power fluctuations. Then, an optimization approach using the Response Surface Method (RSM) is conducted to minimize the annualized cost of the Hybrid Energy Storage System (HESS); consisting of a flywheel, supercapacitor, and battery. The goal is to smooth out the output power fluctuations by the optimal size of the HESS. Thus, a 1.5 MW hydraulic wind turbine is simulated, and the HESS is configured and optimized. The direct connection of the flywheel allows reaching a suitable level of smoothness at a reasonable cost. The proposed configuration is compared with the conventional storage, and the results demonstrate that the proposed integrated HESS can decrease the annualized storage cost by 71 %. Finally, this research investigates the effects of the reduced-size RSC on the Low Voltage Ride Through (LVRT) capabilities required from all wind turbines. One of the significant achievements of an SS-WECS is the reduced size excitation circuit. The grid side converter is eliminated, and the size of the rotor side converter (RSC) can be safely reduced to a fraction of a full-size excitation. Therefore, this low-power-rated converter operates at low voltage and handles the regular operation well. However, the fault conditions may expose conditions on the converter and push it to its limits. Therefore, four different protection circuits are employed, and their effects are investigated and compared to evaluate their performance. These four protection circuits include the active crowbar, active crowbar along a resistorinductor circuit (C-RL), series dynamic resistor (SDR), and new-bridge fault current limiter (NBFCL). The wind turbine controllers are also adapted to reduce the impact of the fault on the power electronic converters. One of the effective methods is to store the excess energy in the generator’s rotor. Finally, the proposed LVRT strategies are simulated in MATLAB Simulink to validate the results and demonstrate their effectiveness and functionality.

Esta Tese trata do controle e integração de centrais eólicas à rede elétrica interligada, utilizando-se geradores de indução duplamente alimentados (GIDE). O objetivo principal da Tese foi desenvolver estratégias de controle discreto para o sistema de geração eólica, de forma a reduzir os impactos na qualidade da energia gerada, em função dos diversos regimes e transitórios de vento, que podem ocorrer no sítio eólico. Para o projeto do sistema de controle dos geradores foi adotada a técnica do controle vetorial, de forma a desacoplar o controle do fluxo das potências ativa e reativa entre o gerador e a rede elétrica. Visando caracterizar os diversos modos de operação do GIDE, com velocidades acima e abaixo da síncrona, foi desenvolvido um estudo de regime permanente do gerador, obtendo-se os limites de correntes, tensões e demais grandezas elétricas e mecânicas, para uma determinada faixa de velocidade. As principais estratégias de controle atualmente utilizadas pelos fabricantes de turbinas eólicas foram analisadas, destacando-se os aspectos da eficiência energética do conjunto turbina-gerador e da qualidade da energia. O projeto das malhas de controle dos conversores estáticos conectados ao circuito do rotor foi desenvolvido utilizando a técnica de controle discreto, propondo-se as estratégias de controle e o conjunto de especificações para definição dos ganhos dos controladores, objetivando reduzir os impactos na qualidade da energia gerada. Foi analisada a influência da modelagem da turbina com eixos elásticos e eixos rígidos, no comportamento das variáveis controladas. Buscando reduzir os harmônicos de ordem elevada da corrente do gerador, devido à modulação por largura de pulso (PWM) dos conversores estáticos, foi proposta uma estratégia de projeto de filtro passivo LCL, instalado no circuito do rotor. Um programa de simulação no ambiente Matlab/Simulinkâ foi desenvolvido, para análise da interligação de um parque eólico, representado por uma turbina equivalente, ao sistema elétrico de potência reduzido, permitindo estudos de regime permanente e transitório. Com este programa, um estudo de caso foi realizado, avaliando-se o controle e a integração de uma usina eólica de 192MW, conectada na rede básica do sistema interligado nacional, na tensão 230kV. Os resultados obtidos mostram as contribuições, das estratégias de controle propostas, para melhorar o comportamento das tensões do sistema elétrico quando da ocorrência de transitórios de ventos na usina. / This Thesis presents the control and integration of wind farms to the interconnected power grid, using doubly fed induction generators (DFIG). The main objective of the present Thesis was to develop discrete control strategies for the wind generation system, with the goal to reduce the wind variations impacts in the grid power quality. The design technique selected for the generators control system was the vector control technique, which allows independent control of active and reactive power flow between the generator and the grid. In order to characterize the diverse operation modes of the DFIG, below and above the synchronous speed, a generator steady-state study was developed, getting the current and voltage limits and the others electric and mechanical safe limits variables, for one determined speed range. The main control strategies currently used by the wind turbines manufacturers were analyzed, highlighting the aspects of the turbine-generator energy efficiency and the power quality. The control loops design of the static converters was developed using the discrete control technique. It was elaborated the control strategies and also the basic specifications used to define the controllers gains, with the key target to reduce the impacts in the grid power quality caused by the wind variations. Other aspect covered by this work was the influence of the turbine modeling, with rigid shafts and with shafts of a relatively low stiffness, in the control system performance. In a way to reduce high order harmonics in the generator current, caused by the pulse width modulation (PWM) of the static converters, it was proposed a design strategy of a passive LCL filter, installed in the rotor circuit. A simulation program was developed, using the Matlab/SimulinkÔ platform, to analyze the interconnection of a wind farm, represented by a equivalent turbine, to the reduced power electrical system, allowing steady-state and transient studies. With this simulation program, a case study was developed evaluating the control and integration of a 192MW wind farm, connected to 230kV voltage level of the national interconnected power system. The main results reached by this work showed the contributions of the control strategies proposed to improve the electrical system voltages behavior, when wind variations occur in the wind farm.

Esta Tese trata do controle e integração de centrais eólicas à rede elétrica interligada, utilizando-se geradores de indução duplamente alimentados (GIDE). O objetivo principal da Tese foi desenvolver estratégias de controle discreto para o sistema de geração eólica, de forma a reduzir os impactos na qualidade da energia gerada, em função dos diversos regimes e transitórios de vento, que podem ocorrer no sítio eólico. Para o projeto do sistema de controle dos geradores foi adotada a técnica do controle vetorial, de forma a desacoplar o controle do fluxo das potências ativa e reativa entre o gerador e a rede elétrica. Visando caracterizar os diversos modos de operação do GIDE, com velocidades acima e abaixo da síncrona, foi desenvolvido um estudo de regime permanente do gerador, obtendo-se os limites de correntes, tensões e demais grandezas elétricas e mecânicas, para uma determinada faixa de velocidade. As principais estratégias de controle atualmente utilizadas pelos fabricantes de turbinas eólicas foram analisadas, destacando-se os aspectos da eficiência energética do conjunto turbina-gerador e da qualidade da energia. O projeto das malhas de controle dos conversores estáticos conectados ao circuito do rotor foi desenvolvido utilizando a técnica de controle discreto, propondo-se as estratégias de controle e o conjunto de especificações para definição dos ganhos dos controladores, objetivando reduzir os impactos na qualidade da energia gerada. Foi analisada a influência da modelagem da turbina com eixos elásticos e eixos rígidos, no comportamento das variáveis controladas. Buscando reduzir os harmônicos de ordem elevada da corrente do gerador, devido à modulação por largura de pulso (PWM) dos conversores estáticos, foi proposta uma estratégia de projeto de filtro passivo LCL, instalado no circuito do rotor. Um programa de simulação no ambiente Matlab/Simulinkâ foi desenvolvido, para análise da interligação de um parque eólico, representado por uma turbina equivalente, ao sistema elétrico de potência reduzido, permitindo estudos de regime permanente e transitório. Com este programa, um estudo de caso foi realizado, avaliando-se o controle e a integração de uma usina eólica de 192MW, conectada na rede básica do sistema interligado nacional, na tensão 230kV. Os resultados obtidos mostram as contribuições, das estratégias de controle propostas, para melhorar o comportamento das tensões do sistema elétrico quando da ocorrência de transitórios de ventos na usina. / This Thesis presents the control and integration of wind farms to the interconnected power grid, using doubly fed induction generators (DFIG). The main objective of the present Thesis was to develop discrete control strategies for the wind generation system, with the goal to reduce the wind variations impacts in the grid power quality. The design technique selected for the generators control system was the vector control technique, which allows independent control of active and reactive power flow between the generator and the grid. In order to characterize the diverse operation modes of the DFIG, below and above the synchronous speed, a generator steady-state study was developed, getting the current and voltage limits and the others electric and mechanical safe limits variables, for one determined speed range. The main control strategies currently used by the wind turbines manufacturers were analyzed, highlighting the aspects of the turbine-generator energy efficiency and the power quality. The control loops design of the static converters was developed using the discrete control technique. It was elaborated the control strategies and also the basic specifications used to define the controllers gains, with the key target to reduce the impacts in the grid power quality caused by the wind variations. Other aspect covered by this work was the influence of the turbine modeling, with rigid shafts and with shafts of a relatively low stiffness, in the control system performance. In a way to reduce high order harmonics in the generator current, caused by the pulse width modulation (PWM) of the static converters, it was proposed a design strategy of a passive LCL filter, installed in the rotor circuit. A simulation program was developed, using the Matlab/SimulinkÔ platform, to analyze the interconnection of a wind farm, represented by a equivalent turbine, to the reduced power electrical system, allowing steady-state and transient studies. With this simulation program, a case study was developed evaluating the control and integration of a 192MW wind farm, connected to 230kV voltage level of the national interconnected power system. The main results reached by this work showed the contributions of the control strategies proposed to improve the electrical system voltages behavior, when wind variations occur in the wind farm.

Αντικείμενο αυτής της διπλωματικής εργασίας είναι η μελέτη και προσομοίωση της λειτουργίας μιας ανεμογεννήτριας μεταβλητών στροφών, η οποία οδηγεί μια ασύγχρονη γεννήτρια διπλής τροφοδότησης, με τη βοήθεια του προγράμματος PSCAD/EMTDC. Γίνεται επίσης μελέτη της λειτουργίας αυτής της ανεμογεννήτριας κατά τη διάρκεια βυθίσεων της τάσης του δικτύου, καθώς και μελέτη της δυνατότητας παραμονής της μηχανής σε λειτουργία κατά τη διάρκεια αυτών των σφαλμάτων. Πιο αναλυτικά, στο πρώτο κεφάλαιο γίνεται αναφορά στις ανανεώσιμες πηγές ενέργειας και ειδικότερα στην αιολική ενέργεια και στο σημαντικό ποσοστό ηλεκτρικής ενέργειας, που καλούνται να συνεισφέρουν στο σύνολο του ενεργειακού μείγματος κάθε χώρας, στο μέλλον. Γίνεται αναφορά στο κόστος παραγωγής ηλεκτρικής ενέργειας με χρήση αιολικής ενέργειας και στη συνέχεια το κόστος αυτό συγκρίνεται με το κόστος της ηλεκτρικής ενέργειας που παράγεται από συμβατικούς σταθμούς. Στο δεύτερο κεφάλαιο γίνεται μία γενική παρουσίαση των αιολικών συστημάτων. Περιγράφονται τα δομικά στοιχεία μιας ανεμογεννήτριας και η αεροδυναμική μετατροπή της κινητικής ενέργειας του ανέμου σε ηλεκτρική. Παρουσιάζονται διάφορες τοπολογίες ανεμογεννητριών που χρησιμοποιούνται σήμερα και στη συνέχεια δίνεται το μαθηματικό μοντέλο της γεννήτριας επαγωγής διπλής τροφοδότησης και οι μετασχηματισμοί σε στρεφόμενα πλαίσια αναφοράς. Κατόπιν γίνεται μελέτη του μετατροπέα πηγής τάσης και αναφέρονται τεχνικές διαμόρφωσης για την παραγωγή των επιθυμητών κυματομορφών. Τέλος, γίνεται σχεδιασμός ενός LCL φίλτρου καταστολής των αρμονικών συνιστωσών των ρευμάτων που εγχύει ο μετατροπέας στο δίκτυο. Στο τρίτο κεφάλαιο περιγράφεται ο διανυσματικός έλεγχος και γίνεται εφαρμογή του στον έλεγχο του μετατροπέα προς την πλευρά του δρομέα και στον έλεγχο του μετατροπέα προς την πλευρά του δικτύου. Παρουσιάζεται η γενική στρατηγική ελέγχου της ανεμογεννήτριας με χρήση του ελέγχου βήματος πτερυγίου για τον περιορισμό της παραγώμενης ισχύος στις υψηλές ταχύτητες ανέμου. Όταν η ταχύτητα του ανέμου είναι μικρότερη της ονομαστικής, τότε η ταχύτητα της μηχανής και η παραγώμενη ισχύς ακολουθούν την χαρακτηριστική ισχύος – ταχύτητας, που εξασφαλίζει βέλτιστη λειτουργία. Γίνεται προσομοίωση της λειτουργίας της ανεμογεννήτριας και εκτίμηση της απόκρισης σε βηματικές αλλαγές της ταχύτητας του ανέμου. Στο τέταρτο κεφάλαιο γίνεται μελέτη παραμονής της ανεμογεννήτριας σε λειτουργία, κατά τη διάρκεια βύθισης της τάσης του δικτύου και ανάλυση μεθόδων υλοποίησης αυτού του στόχου. Με την ανίχνευση του σφάλματος ο δρομέας βραχυκυκλώνεται και ο μετατροπέας προς την πλευρά του δρομέα αποσυνδέεται, ενώ οι διακόπτες του αποκόπτονται για να προστατευθούν από το υψηλό ρεύμα του δρομέα. Μόλις το ρεύμα του δρομέα πέσει και πάλι κάτω από την ανώτατη επιτρεπτή τιμή, ο μετατροπέας συνδέεται και πάλι με τον δρομέα για να ανακτήσει τον έλεγχο της παραγώμενης από τον στάτη ενεργού και αέργου ισχύος. Αμέσως παράγεται άεργος ισχύς για την στήριξη της τάσης του δικτύου, ενώ μειώνεται η παραγωγή ενεργού ισχύος, έτσι ώστε το συνολικό ρεύμα του δρομέα να παραμείνει μέσα στα επιτρεπτά όρια. Με την αποκατάσταση της τάσης του δικτύου, η παραγώμενη ενεργός και άεργος ισχύς παίρνουν σταδιακά τις τιμές που είχαν πριν την εκδήλωση του σφάλματος. / -

A geração de energia elétrica com fontes renováveis está em aumento e uma das que tem maior crescimento é a eólica. A instalação das máquinas que aproveitam este recurso pode trazer alguns problemas para a rede elétrica devido à intermitência da velocidade do vento. O presente trabalho tem por objetivo analisar o comportamento de dois tipos de aerogeradores que utilizam gerador de indução e sua interação com o sistema elétrico de potência. Os aerogeradores assíncronos analisados são o de velocidade variável com gerador de indução duplamente alimentado (Doubly-Fed Induction Generator-DFIG) e o de velocidade fixa com gerador de indução de rotor de gaiola de esquilo (Squirrel Cage Induction Generator-SCIG). O caso de estudo está baseado no parque eólico Jepirachi na Colômbia, o qual na atualidade tem aerogeradores de velocidade fixa. Para isto inicialmente foi feita a modelagem do parque eólico considerando alguns parâmetros dos aerogeradores comerciais de velocidade variável e velocidade fixa, junto com os principais componentes da rede elétrica da região para obter uma aproximação da mesma. Posteriormente realizaram-se simulações computacionais para obter o comportamento do sistema elétrico de potência alimentado por estes tipos de aerogeradores. Finalmente, foi realizada uma análise dos efeitos que produzem cada tipo de máquina, no fluxo de potência e no nível de tensão da rede elétrica funcionando em regime permanente, considerando os distúrbios ocasionados pelas mudanças da velocidade do vento. / The generation of electricity from renewable sources is increasing, one of the largest growth is the wind power. However the installation of the machines that leverage this resource could bring some problems to the grid due to the intermittency of the wind speed. This work analyzes the behavior of variable speed wind turbines with Doubly-Fed Induction Generator (DFIG) and fixed-speed wind turbines with Squirrel Cage Induction Generator (SCIG). The case study is based in Jepirachi wind farm in Colombia, that at the present has fixed-speed wind turbines with Squirrel Cage Induction Generator (SCIG). To do this study, initially the modeling of the wind farm considering some parameters of commercial wind turbines with variable speed and fixed speed, also modeling the main components of the electric grid of the region to obtain an approximation of it, after computer simulations we made in order to obtain the behavior of the electric power system powered by these types of turbines. Finally the analysis of the effects produced by each type of machine, in the power flow and the voltage level of the grid operating in steady state, but considering the disturbances caused by changes in wind speed are made.

Neste momento o Brasil possui uma das mais renováveis matrizes energéticas do mundo, mas o desafio de reduzir os níveis de emissão, permitir o crescimento econômico e atender a aproximadamente um milhão de pessoas sem energia elétrica no pais, requer a pesquisa e o desenvolvimento de novas tecnologias que possibilitem a utilização de fontes limpas e sustentáveis de energia, como é a energia eólica. A energia eólica é considerada, entre as alternativas renováveis existentes, a mais viável no mercado de energia, devido à baixa relação custo/benefício de exploração, tendo apresentado um crescimento exponencial ao longo dos anos. Os principais sistema eólicos classificam-se de acordo com sua operação em dois tipos: sistemas com operação a velocidade fixa e sistemas com operação a velocidade variável. Durante muitos anos a liderança do mercado foi para os geradores que operam a velocidade fixa, sendo a máquina mais usada o gerador de indução de rotor em gaiola (SCIG). A partir do ano 2000, a supremacia no mercado passou a ser para o gerador de velocidade variável. Hoje, tem-se dois tipos de geradores amplamente utilizados em sistemas eólicos que operam a velocidade variável: o gerador síncrono e o gerador de indução com rotor bobinado. Neste trabalho será estudada uma das máquinas que operam a velocidade variável e utilizam geradores de indução com rotor bobinado: o gerador de indução duplamente alimentado (DFIG). Sua importância é principalmente o controle independente da potência ativa e da potência reativa fornecida para a rede elétrica, e à operação com máxima eficiência na conversão de energia. Neste contexto, este trabalho apresenta uma análise comparativa de um sistema de geração utilizando máquinas do tipo DFIG com quatro estratégias de controle: controle da potência ativa e da tensão nos terminais da máquina, controle da potência reativa e da tensão nos terminais da máquina, controle da velocidade de rotação e da tensão nos terminais da máquina, controle da potência ativa e da potência reativa fornecidas pela máquina ao sistema. Esta análise é feita comparando o comportamento do sistema quando sujeito a diversas situações, tais como: variações da demanda de potência da carga elétrica, variações do torque mecânico e ocorrência de uma falta trifásica. O desempenho de sistemas de geração eólica com SCIG também é incluído nesta análise para ilustrar de maneira quantitativa os ganhos obtidos com o uso do DFIG. Os resultados obtidos ilustram as virtudes de cada uma das diferentes possibilidades de modos de operação do DFIG em um sistema de distribuição e permitem uma melhor compreensão da vantagem do desempenho do DFIG em relação à utilização do SCIG. / At present Brazil has one of the most renewable energy matrices in the world, but the challenge of reducing emission levels, allowing the economic growth, and helping about 1 million people without electric energy in the country, requires research and development of new technologies that enable the use of clean and sustainable energy sources, such as wind power. Wind energy is considered among the existing renewable alternatives the more viable in the energy market, due to the low cost / benefit ratio of exploitation, having experienced exponential growth over the years. The wind system are classified according to their operation into two types: operating systems with fixed speed and systems with variable speed operation. For many years the leadership in the market was for fixed speed generator, being the most used machine, the induction generator rotor cage (SCIG). From 2000, the leadership in the market was for variable speed wind turbine. Today, there are two types of wind generators widely used in systems that operate at variable speed: synchronous generator and generator with wound rotor induction. In this work we will study one of the machines that operate at variable speed and use induction generators with wound rotor: the doubly-fed induction generator (DFIG). Its importance is mainly the independent control of active power and reactive power supplied to the grid, and operating at maximum efficiency in energy conversion. In this context, this work presents a comparative analysis of a generation system using DFIG type machines with four control strategies: control of active power and voltage at the terminals of the machine, control of reactive power and voltage at the machine terminals, control the rotational speed and tension in the machine terminals, control of active power and reactive power supplied by the machine. This analysis is done by comparing the behavior of the system when subjected to various situations, such as variations in power demand of electric load, changes in the mechanical torque and the occurrence of a three-phase fault. The performance of wind power generation systems with SCIG is also included in this analysis to illustrate quantitatively the gains obtained using DFIG. The results illustrate the virtues of each of the different possible operating modes of the DFIG in a distribution system and allow a better understanding of the performance advantage of the machine DFIG over the use of the machine SCIG.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / This dissertation addresses the main problems related to doubly-fed induction generators (DFIG) connection to grids with unbalanced voltages. Series compensation is used to achieve balanced voltage on the stator of the machine, avoiding torque oscillations and high currents due to the grid voltage unbalance. The DC-link voltage control proposed reduces the complexity of the converter when compared to the alternatives considered in the literature. The close to no-load operation of the DFIG is also depicted. Simulation results for a commercial large scale generator are presented to demonstrate the performance of the system with the proposed controller. / Esta dissertação trata dos principais problemas relacionados à conexão de geradores duplamente alimentados à rede elétrica com tensões desequilibradas. Compensação série é usada para equilibrar as tensões no estator da máquina, evitando oscilações de conjugado e altas correntes de seqüência negativa devido aos desequilíbrios das tensões no ponto de conexão do gerador. O controle da tensão do barramento CC é proposto tal que é possível reduzir a complexidade do conversor quando comparado com outras alternativas apresentadas na literatura. A operação próximo à carga nula é apresentada. Resultados de simulação para um gerador em escala comercial são apresentados para demonstrar o desempenho do sistema proposto.

A geração de energia elétrica com fontes renováveis está em aumento e uma das que tem maior crescimento é a eólica. A instalação das máquinas que aproveitam este recurso pode trazer alguns problemas para a rede elétrica devido à intermitência da velocidade do vento. O presente trabalho tem por objetivo analisar o comportamento de dois tipos de aerogeradores que utilizam gerador de indução e sua interação com o sistema elétrico de potência. Os aerogeradores assíncronos analisados são o de velocidade variável com gerador de indução duplamente alimentado (Doubly-Fed Induction Generator-DFIG) e o de velocidade fixa com gerador de indução de rotor de gaiola de esquilo (Squirrel Cage Induction Generator-SCIG). O caso de estudo está baseado no parque eólico Jepirachi na Colômbia, o qual na atualidade tem aerogeradores de velocidade fixa. Para isto inicialmente foi feita a modelagem do parque eólico considerando alguns parâmetros dos aerogeradores comerciais de velocidade variável e velocidade fixa, junto com os principais componentes da rede elétrica da região para obter uma aproximação da mesma. Posteriormente realizaram-se simulações computacionais para obter o comportamento do sistema elétrico de potência alimentado por estes tipos de aerogeradores. Finalmente, foi realizada uma análise dos efeitos que produzem cada tipo de máquina, no fluxo de potência e no nível de tensão da rede elétrica funcionando em regime permanente, considerando os distúrbios ocasionados pelas mudanças da velocidade do vento. / The generation of electricity from renewable sources is increasing, one of the largest growth is the wind power. However the installation of the machines that leverage this resource could bring some problems to the grid due to the intermittency of the wind speed. This work analyzes the behavior of variable speed wind turbines with Doubly-Fed Induction Generator (DFIG) and fixed-speed wind turbines with Squirrel Cage Induction Generator (SCIG). The case study is based in Jepirachi wind farm in Colombia, that at the present has fixed-speed wind turbines with Squirrel Cage Induction Generator (SCIG). To do this study, initially the modeling of the wind farm considering some parameters of commercial wind turbines with variable speed and fixed speed, also modeling the main components of the electric grid of the region to obtain an approximation of it, after computer simulations we made in order to obtain the behavior of the electric power system powered by these types of turbines. Finally the analysis of the effects produced by each type of machine, in the power flow and the voltage level of the grid operating in steady state, but considering the disturbances caused by changes in wind speed are made.