Rozprawy doktorskie: „Fed induction generator based microgrid”

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Subramanian, Chandrasekaran <1983&gt. "Grid Connected Doubly Fed Induction Generator Based Wind Turbine under LVRT". Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amsdottorato.unibo.it/6243/1/Grid_Connected_Doubly_Fed_Induction_Generator_Based_Wind_Turbine_under_LVRT.pdf.

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This project concentrates on the Low Voltage Ride Through (LVRT) capability of Doubly Fed Induction Generator (DFIG) wind turbine. The main attention in the project is, therefore, drawn to the control of the DFIG wind turbine and of its power converter and to the ability to protect itself without disconnection during grid faults. It provides also an overview on the interaction between variable speed DFIG wind turbines and the power system subjected to disturbances, such as short circuit faults. The dynamic model of DFIG wind turbine includes models for both mechanical components as well as for all electrical components, controllers and for the protection device of DFIG necessary during grid faults. The viewpoint of this project is to carry out different simulations to provide insight and understanding of the grid fault impact on both DFIG wind turbines and on the power system itself. The dynamic behavior of DFIG wind turbines during grid faults is simulated and assessed by using a transmission power system generic model developed and delivered by Transmission System Operator in the power system simulation toolbox Digsilent, Matlab/Simulink and PLECS.

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Subramanian, Chandrasekaran <1983&gt. "Grid Connected Doubly Fed Induction Generator Based Wind Turbine under LVRT". Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amsdottorato.unibo.it/6243/.

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This project concentrates on the Low Voltage Ride Through (LVRT) capability of Doubly Fed Induction Generator (DFIG) wind turbine. The main attention in the project is, therefore, drawn to the control of the DFIG wind turbine and of its power converter and to the ability to protect itself without disconnection during grid faults. It provides also an overview on the interaction between variable speed DFIG wind turbines and the power system subjected to disturbances, such as short circuit faults. The dynamic model of DFIG wind turbine includes models for both mechanical components as well as for all electrical components, controllers and for the protection device of DFIG necessary during grid faults. The viewpoint of this project is to carry out different simulations to provide insight and understanding of the grid fault impact on both DFIG wind turbines and on the power system itself. The dynamic behavior of DFIG wind turbines during grid faults is simulated and assessed by using a transmission power system generic model developed and delivered by Transmission System Operator in the power system simulation toolbox Digsilent, Matlab/Simulink and PLECS.

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Wang, Lei. "Advanced control of doubly-fed induction generator based variable speed wind turbine". Thesis, University of Liverpool, 2012. http://livrepository.liverpool.ac.uk/10575/.

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This thesis deals with the modeling, control and analysis of doubly fed induction generators (DFIG) based wind turbines (DFIG-WT). The DFIG-WT is one of the mostly employed wind power generation systems (WPGS), due to its merits including variable speed operation for achieving the maximum power conversion, smaller capacity requirement for power electronic devices, and full controllability of active and reactive powers of the DFIG. The dynamic modeling of DFIG-WT has been carried out at first in Chapter 2, with the conventional vector control (VC) strategies for both rotor-side and grid-side converters. The vector control strategy works in a synchronous reference frame, aligned with the stator-flux vector, became very popular for control of the DFIG. Although the conventional VC strategy is simple and reliable, it is not capable of providing a satisfactory transient response for DFIG-WT under grid faults. As the VC is usually designed and optimized based on one operation point, thus the overall energy conversion efficiency cannot be maintained at the optimal point when the WPGS operation point moves away from that designed point due to the time-varying wind power inputs. Compared with VC methods which are designed based on linear model obtained from one operation point, nonlinear control methods can provide consistent optimal performance across the operation envelope rather than at one operation point. To improve the asymptotical regulation provided by the VC, which can't provide satisfactory performance under voltage sags caused by grid faults or load disturbance of the grid, input-output feedback linearization control (IOFLC) has been applied to develop a fully decoupled controller of the active $\&$ reactive powers of the DFIG in Chapter 3. Furthermore, a cascade control strategy is proposed for power regulation of DFIG-WT, which can provide better performance against the varying operation points and grid disturbance. Moreover, to improve the overall energy conversion efficiency of the DFIG-WT, FLC-based maximum power point tracking (MPPT) has been investigated. The main objective of the FLC-based MPPT in Chapter 4 is to design a global optimal controller to deal with the time-varying operation points and nonlinear characteristic of the DFIG-WT. Modal analysis and simulation studies have been used to verify the effectiveness of the FLC-based MPPT, compared with the VC. The system mode trajectory, including the internal zero-dynamic of the FLC-MPPT are carefully examined in the face of varied operation ranges and parameter uncertainties. In a realistic DFIG-WT, the parameter variability, the uncertain and time-varying wind power inputs are existed. To enhance the robustness of the controller, a nonlinear adaptive controller (NAC) via state and perturbation observer for feedback linearizable nonlinear systems is applied for MPPT control of DFIG-WT in Chapter 5. In the design of the controller, a perturbation term is defined to describe the combined effect of the system nonlinearities and uncertainties, and represented by introducing a fictitious state in the state equations. As follows, a state and perturbation observer is designed to estimate the system states and perturbation, leading to an adaptive output-feedback linearizing controller which uses the estimated perturbation to cancel system perturbations and the estimated states to implement a linear output feedback control law for the equivalent linear system. Case studies including with and without wind speed measurement are carried out and proved that the proposed NAC for MPPT of DFIG-WT can provide better robustness performance against the parameter uncertainties. Simulation studies for demonstrating the performance of the proposed control methods in each chapter, are carried out based on MATLAB/SIMULINK.

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Shi, Kai. "Advanced control of doubly-fed induction generator based wind turbines for dynamic performance improvement". Thesis, University of Liverpool, 2017. http://livrepository.liverpool.ac.uk/3018211/.

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Yunus, A. M. Shiddiq. "Application of SMES Unit to improve the performance of doubly fed induction generator based WECS". Thesis, Curtin University, 2012. http://hdl.handle.net/20.500.11937/1450.

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Due to the rising demand of energy over several decades, conventional energy resources have been continuously and drastically explored all around the world. As a result, global warming is inevitable due to the massive exhaust of CO2 into the atmosphere from the conventional energy sources. This global issue has become a high concern of industrial countries who are trying to reduce their emission production by increasing the utilization of renewable energies such as wind energy. Wind energy has become very attractive since the revolution of power electronics technology, which can be equipped with wind turbines. Wind energy can be optimally captured with wind turbine converters. However, these converters are very sensitive if connected with the grid as grid disturbances may have a catastrophic impact on the overall performance of the wind turbines.In this thesis, superconducting magnetic energy storage (SMES) is applied on wind energy conversion systems (WECSs) that are equipped with doubly fed induction generators (DFIGs) during the presence of voltage sags and swells in the grid side. Without SMES, certain levels of voltage sags and swells in the grid side may cause a critical operating condition that may require disconnection of WECS to the grid. This condition is mainly determined by the voltage profile at the point of common coupling (PCC), which is set up differently by concerned countries all over the world. This requirement is determined by the transmission system operator (TSO) in conjunction with the concerned government. The determined requirement is known as grid codes or fault ride through (FRT) capability.The selection of a SMES unit in this thesis is based on its advantages over other energy storage technologies. Compared to other energy storage options, the SMES unit is ranked first in terms of highest efficiency, which is 90-99%. The high efficiency of the SMES unit is achieved by its low power loss because electric currents in the coil encounter almost no resistance and there are no moving parts, which means no friction losses. Meanwhile, DFIG is selected because it is the most popular installed WECS over the world. In 2004 about 55% of the total installed WECS worldwide were equipped with DFIG. There are two main strategies that can be applied to meet the grid requirements of a particular TSO. The first strategy is development of new control techniques to fulfil the criterion of the TSOs. This strategy, however, is applicable only to the new WECS that have not been connected to the power grid. If new control techniques are applied to the existing gridconnected WECSs, they will not be cost effective because the obsolete design must be dismantled and re-installed to comply with current grid code requirements. The second strategy is the utilization of flexible AC transmission system (FACTS) devices or storage energy devices to meet the grid code requirements. This strategy seems more appropriate for implementation in the existing WECS-grid connection in order to comply with the current grid code requirements. By appropriate design, the devices might be more cost effective compared to the first strategy, particularly for the large wind farms that are already connected to the grid.A new control algorithm of a SMES unit, which is simple but still involves all the important parameters, is employed in this study. Using the hysteresis current control approach in conjunction with a fuzzy logic controller, the SMES unit successfully and effectively improves the performance of the DFIG during voltage sag and swell events in the grid side; thus, this will prevent the WECS equipped with DFIG from being disconnected from the grid according to the selected fault ride through used in this study. The dynamic study of DFIG with SMES during short load variation is carried out as an additional advantage of SMES application on a DFIG system. In this study, the proposed SMES unit is controlled to compensate the reduced transfer power of DFIG during the short load variation event. Moreover, the SMES unit is also engaged in absorbing/storing some amount of excessive power that might be transferred to the grid when the local loads are suddenly decreased. Finally, the studies of intermittent misfires and fire-through that take place within the converters of DFIG are carried out in order to investigate the impact of these converter faults on the performance of DFIG. In this part, the proposed SMES unit is controlled to effectively improve the DFIG’s performance in order to prevent it from being disconnected or shut down from the power grid during the occurrence of these intermittent switching faults.

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Zafar, Jawwad. "Winding short-circuit fault modelling and detection in doubly-fed induction generator based wind turbine systems". Doctoral thesis, Universite Libre de Bruxelles, 2011. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209854.

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Abstract

This thesis deals with the operation of and winding short-circuit fault detection in a Doubly-Fed Induction Generator (DFIG) based Wind Turbine Generator System (WTGS). Both the faulted and faultless condition of operation has been studied, where the focus is on the electrical part of the system. The modelled electrical system is first simulated and the developed control system is then validated on a test bench. The test-bench component dimensioning is also discussed.

The faultless condition deals with the start-up and power production mode of operation. Control design based on the Proportional Integral (PI) control technique has been compared for power and torque control strategies against the Linear Quadratic Gaussian (LQG) control technique, at different operating points through the variable-speed region of WTGS operation following the maximum power curve of the system. It was found that the torque control strategy offered less degradation in performance for both the control techniques at operating points different for the one for which the control system was tuned. The start-up procedure of the DFIG based WTGS has been clarified and simplified. The phase difference between the stator and the grid voltage, which occurs due to the arbitrary rotor position when the rotor current control is activated, is minimized by using a sample-and-hold technique which eliminates the requirement of designing an additional controller. This method has been validated both in simulation and experiments.

The faulted condition of operation deals with the turn-turn short-circuit fault in the phase winding of the generator. The model of the generator, implemented using the winding-function approach, allows the fault to be created online both in a stator and a rotor phase. It has been demonstrated that the magnitude of the current harmonics, used extensively in literature for the Machine Current Signature Analysis (MCSA) technique for winding short-circuit fault detection, is very different when the location of the fault is changed to another coil within the phase winding. This makes the decision on the threshold selection for alarm generation difficult. Furthermore, the control system attenuates the current harmonics by an order of magnitude. This attenuation property is also demonstrated through experiments. The attention is then shifted to the negative-sequence current component, resulting from the winding unbalance, as a possible fault residual. Its suitability is tested in the presence of noise for scenarios with different fault locations, fault severity in terms of the number of shorted-turns and grid voltage unbalance. It is found that due to the presence of a control system the magnitude of the negative-sequence current, resulting from the fault, remains almost the same for all fault locations and fault severity. Thus, it was deemed more suitable as a fault residual. In order to obtain a fast detection method, the Cumulative Sum (CUSUM) algorithm was used. The test function is compared against a threshold, determined on the basis of expected residual magnitude and the time selected for detection, to generate an alarm. The validation is carried out with noise characteristics different from the ones used during the design and it is shown that the voltage unbalance alone is not able to trigger a false alarm. In all the scenarios considered, the detection was achieved within 40 ms despite the presence of measurement filters.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

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Kareem, Amer Obaid. "Performance analysis of doubly-fed induction generator (DFIG)-based wind turbine with sensored and sensorless vector control". Thesis, University of Newcastle upon Tyne, 2016. http://hdl.handle.net/10443/3539.

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Conventional energy sources are limited and pollute the environment. Therefore more attention has been paid to utilizing renewable energy resources. Wind energy is the fastest growing and most promising renewable energy source due to its economically viability. Wind turbine generator systems (WTGSs) are being widely manufactured and their number is rising dramatically day by day. There are different generator technologies adopted in wind turbine generator systems, but the most promising type of wind turbine for the future market is investigated in the present study, namely the doubly-fed induction generator wind turbine (DFIG). This has distinct advantages, such as cost effectiveness, efficiency, less acoustic noise, and reliability and in addition this machine can operate either in grid-connected or standalone mode. This investigation considers the analysis, modeling, control, rotor position estimation and impact of grid disturbances in DFIG systems in order to optimally extract power from wind and to accurately predict performance. In this study, the dynamic performance evaluation of the DFIG system is depicted the power quantities (active and reactive power) are succeed to track its command signals. This means that the decouple controllers able to regulating the impact of coupling effect in the tracking of command signals that verify the robust of the PI rotor active power even in disturbance condition. One of the main objectives of this study is to investigate the comparative estimation analysis of DFIG-based wind turbines with two types of PI vector control using PWM. The first is indirect sensor vector control and the other type includes two schemes using model reference adaptive system (MRAS) estimators to validate the ability to detect rotor position when the generator is connected to the grid. The results for the DFIG-based on reactive power MRAS (QRMRAS) are compared with those of the rotor current-based MRAS (RCMRAS) and the former scheme proved to be better and less sensitive to parameter deviations, its required few mathematical computations and was more accurate. During the set of tests using MATLAB®/SMULINK® in adjusting the error between the reference and adaptive models, the estimated rotor position can be obtained with the objective of achieving accurate rotor position information, which is usually measured by rotary encoders or resolvers. The use of these encoders will conventionally lead to increased cost, size, weight, and wiring ii complexity and reduced the mechanical robustness and reliability of the overall DFIG drive systems. However the use of rotor position estimation represents a backup function in sensor vector control systems when sensor failure occurs. The behavioral response of the DFIG-based wind turbine system to grid disturbances is analyzed and simulated with the proposed control strategies and protection scheme in order to maintain the connection to the network during grid faults. Moreover, the use of the null active and reactive reference set scheme control strategy, which modifies the vector control in the rotor side converter (RSC) contributes to limiting the over-current in the rotor windings and over-voltage in the DC bus during voltage dips, which can improve the Low Voltage Ride-through (LVRT) ability of the DFIG-based wind turbine system.

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Naggar, Ahmed el [Verfasser], i István [Akademischer Betreuer] Erlich. "Advanced modeling and analysis of the doubly-fed induction generator based wind turbines / Ahmed El Naggar ; Betreuer: István Erlich". Duisburg, 2017. http://d-nb.info/1139640623/34.

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Baggu, Murali Mohan. "Advanced control techniques for doubly fed induction generator-based wind turbine converters to improve low voltage ride-through during system imbalances". Diss., Rolla, Mo. : Missouri University of Science and Technology, 2009. http://scholarsmine.mst.edu/thesis/pdf/Baggu_09007dcc806684bd.pdf.

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Thesis (Ph. D.)--Missouri University of Science and Technology, 2009.
Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed May 27, 2009) Includes bibliographical references (p. 126-130).

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Khamaira, Mahmoud Yousef. "A New Converter Station Topology to Improve the Overall Performance of a Doubly Fed Induction Generator-Based Wind Energy Conversion System". Thesis, Curtin University, 2015. http://hdl.handle.net/20.500.11937/2397.

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This thesis presents a reliable and cost effective technique that calls for reconfiguration of the existing converters of a typical Doubly Fed Induction Generator to include a coil of low internal resistance. A coil within the DC link is the only hardware component required to implement this technique. With a proper control scheme, activated during fault conditions, this coil can provide the same degree of performance as a superconducting magnetic energy storage unit during fault conditions.

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Naranjo, Rafael Ricardo Avila. "Alternatives to the use of the crowbar circuit in DFIG based wind turbines during balanced voltage dips". Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/3/3143/tde-30122014-112624/.

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Most of the modern wind turbines are based on doubly fed induction generators (DFIG), with a back to back power converter connecting the rotor to the network. It is known that voltage dips at the stator terminals can cause overcurrents in the rotor windings, which could threaten the converter integrity. In order to protect the converter, several strategies have been proposed in technical literature, requiring in some cases the converter deactivation, which disables the control that the converter has over the power transference between the generator and the system. This last is not a desirable behavior since it can put on risk the voltage stability of the electric system. It is the aim of this dissertation to introduce and compare five of those protection strategies, through the computational simulation of their performance in case of balanced voltage dips. In order to achieve this, the electromagnetic dynamic model of the DFIG was theoretically developed, as well as the models of the strategies of interest. Subsequently, the computational model of the system was assembled in the software Matlabs Simulink to finally perform the desired simulations and its corresponding analysis.
A maioria das turbinas eólicas modernas é baseada em geradores de indução duplamente alimentados (GIDE), com um back to back conversor de energia que liga o rotor para a rede. Sabe-se que as quedas de tensão nos terminais do estator podem causar sobrecorrentes nos enrolamentos do rotor, que podem ameaçar a integridade do conversor. A fim de proteger o conversor, várias estratégias têm sido propostas na literatura técnica, exigindo, em alguns casos, a desativação do conversor, o qual desativa o controlo do conversor, que possui ao longo da transferência de energia entre o gerador e o sistema. Este último não é um comportamento desejável, uma vez que pode colocar em risco a estabilidade de tensão do sistema elétrico. É o objetivo desta dissertação apresentar e comparar cinco dessas estratégias de proteção, através da simulação computacional de seu desempenho em caso de quedas de tensão equilibrada. A fim de alcançar este objetivo, o modelo dinâmico eletromagnética do DFIG teoricamente foi desenvolvido, bem como os modelos das estratégias de interesse. Subsequentemente, o modelo computacional do sistema foi montado no software Simulink do Matlab para finalmente executar as simulações desejadas e sua análise correspondente.

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Wang, Ge. "Doubly fed induction generator (DFIG)-based wind power generation system simulation using real-time digital simulator (RTDS) a thesis presented to the faculty of the Graduate School, Tennessee Technological University /". Click to access online, 2009. http://proquest.umi.com/pqdweb?index=0&did=2000377761&SrchMode=1&sid=4&Fmt=6&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1277818196&clientId=28564.

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Alsmadi, Yazan M. "Modeling, Advance Control, and Grid Integration of Large-Scale DFIG-Based Wind Turbines during Normal and Fault Ride-Through Conditions". The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1437140573.

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Soued, Salah. "The DFIG Based Wind Farms and their impact on electrical Power Systems". Thesis, Bourgogne Franche-Comté, 2019. http://www.theses.fr/2019UBFCA017.

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Traditionnellement, les éoliennes fonctionnaient de manière à extraire le maximum d’énergie du vent dans différentes conditions de fonctionnement. Par conséquent, les éoliennes ont été conçues pour fonctionner en mode connecté au réseau ou en mode autonome. En outre, les innovations récentes dans les micro-réseaux ont suscité l’intérêt pour le fonctionnement autonome de l’éolienne, dans le cadre de réseaux isolés, ou pour les générateurs distribués dans les réseaux faibles.Un autre domaine d’application intéressant concerne les parcs éoliens offshores connectés au réseau via une liaison à courant continu haute tension (HVDC). Dans ces systèmes, le parc éolien offshore est isolé du réseau. Alors que, dans la technologie à convertisseur de tension (VSC) -HVDC, la tension du parc éolien est fournie par le redresseur VSC, si un redresseur HVDC à convertisseur de ligne est utilisé, la tension doit être générée par les éoliennes, qui fonctionnent maintenant de manière isolée.Contrairement aux modes connectés au réseau, une éolienne en fonctionnement autonome et en îlot doit imposer et maintenir une tension et une fréquence tout en faisant correspondre la production et la charge, malgré les variations de la vitesse du rotor dues aux variations de la vitesse du vent et des charges. Lorsque la génération dépasse les charges demandées, elle doit être réduite en contrôlant l'angle de pas des pales. D'autre part, si la génération n'est pas suffisante pour alimenter les charges, le mécanisme de délestage doit être utilisé. Ainsi, les exigences de fonctionnement autonome impliquent que les éoliennes doivent avoir un contrôle actif de la puissance via un contrôle aérodynamique et un contrôle des convertisseurs électroniques de puissance. Les technologies d'éoliennes qui répondent à ces exigences sont celles basées sur des générateurs à vitesse variable et le contrôle du tangage. De nos jours, parmi ces technologies, les GADA ont été utilisés comme la meilleure option. La GADA a plus de liberté pour contrôler les deux convertisseurs. Le contrôle du convertisseur côté grille (GSC) permet de réguler la tension du bus CC et le convertisseur du côté rotor (RSC) commande la machine.Dans cette thèse, la commande du DFIG fournissant une charge isolée est présentée. De plus, le système de contrôle vectoriel (FOC) est utilisé pour fournir une tension et une fréquence constantes du GADA en fonctionnement autonome lorsque les variations de la charge et de la vitesse du rotor sont très fiables et robustes
Traditionally, wind turbines have been operated to extract maximum energy output from wind under different operating conditions. Therefore, wind turbines have been designed to work either in the grid connected mode or stand-alone mode. In addition, recent innovations in micro-grids have aroused the interest in the stand-alone operation of the wind turbine, as part of isolated grids, or the distributed generators in weak networks.Furthermore, another interesting application of the wind energy system is the offshore wind farms grid connected via a High-Voltage Direct Current (HVdc) link. In these applications, the offshore wind farm is isolated from the grid. Whereas in Voltage-Sourced Converter (VSC)-HVdc technology the wind farm voltage is supplied by the VSC rectifier, if a line-commutated converter HVdc rectifier is utilized, the voltage must be generated by the wind turbine generators, which are now operating in the isolated grid.Unlike in grid-connected modes, a wind turbine in stand-alone and islanding operation must impose and maintain voltage and frequency while matching generation and load, even with varying rotor speed and loads variations. When generation exceeds the demanded loads, generation must be reduced by controlling the pitch angle of blades. Besides, the load shedding mechanism should be used if the generation is not enough to supply the loads. Thus, stand-alone operation requirements must have active power control through power electronic converters control. The wind turbine technologies that meet these requirements are those based on variable speed generators and pitch control. Nowadays, among these technologies, DFIGs has been used as the best option. The DFIG has more freedom to control the two converters. Grid Side Converter (GSC) control to regulate the DC bus voltage and the Rotor Side Converter (RSC) controls the machine.In this thesis, the control of the DFIG supplying an isolated load is presented. Moreover, Field Oriented Control (FOC) Vector Control (VC) scheme is used to provide constant voltage and frequency of the DFIG in stand-alone operation when variations in both load and rotor speed in a very reliable and robust way

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Tiwari, Shailendra Kumar. "Investigations on doubly fed induction generator based microgrid using renewable energy resources". Thesis, 2018. http://eprint.iitd.ac.in:80//handle/2074/8002.

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Lin, Bo-Nian, i 林柏年. "Microgrid Frequency Improvement Using a Model Predictive Controller for Doubly Fed Induction Generator". Thesis, 2018. http://ndltd.ncl.edu.tw/handle/9j7z9z.

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碩士
國立臺灣大學
電機工程學研究所
106
Design of a model predictive auxiliary frequency controller and maximum power tracking compensator for a doubly-fed induction generator (DFIG) in a microgrid is investigated in this thesis. When there’s frequency change in a microgrid, the conventional approach is to rely on the inertia control, primary control, and secondary control of synchronous generators to stabilize the system frequency. With the increasing need of green energy, some of the traditional synchronous generators are replaced by wind turbine generators. If the wind turbine generators are not provided with auxiliary frequency controller mechanism, satisfactory frequency response can not be achieved. Therefore, the wind turbines must be designed with the auxiliary frequency controller in order to improve system frequency response. In a doubly-fed induction generator (DFIG), the auxiliary frequency controller is usually installed on the rotor side converter (RSC) and frequency regulation is achieved through a droop control signal which is proportional to frequency deviation and the torque reference command of the RSC is modulated through this droop control input. In previous works, the gain of the auxiliary frequency controller was fixed. However, a fixed-gain auxiliary frequency controller is not able to provide satisfactory frequency response when there is a change in generator parameter or wind speed. Moreover, underfrequency load shedding must be enforced when the frequency deviation exceeds the preset value. In the present work, a model predictive auxiliary frequency controller is designed for the DFIG in order to improve frequency response in a microgrid. The plant predictive model will change when there is a change in generator parameter or wind speed. As a result, better frequency response can be achieved with the adaptive control provided by the proposed model predictive auxiliary frequency controller. Furthermore, underfrequency load shedding can be avoided with the implementation of state variable (frequency) constraint in the model predictive auxiliary frequency controller. When there is a change in system frequency, the auxiliary frequency controller of the wind turbines would provide the needed active power to the system timely. In the dynamic process, the rotating speed of the wind turbine would decrease. As a result, the maximum power tracking control and frequency compensation are affected. Therefore, the investigation of maximum power tracking compensator is required. The research results show that, with maximum power tracking compensator, the frequency response in the dynamic process can be improved. In order to demonstrate the effectiveness of the proposed model predictive auxiliary frequency controller and maximum power tracking compensator, MATLAB/Simulink dynamic simulation are performed on a microgrid in central Taiwan which comprises conventional synchronous generators and off-shore wind farms.

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Faria, Keith Joseph. "Doubly-fed induction generator based wind power plant models". Thesis, 2009. http://hdl.handle.net/2152/ETD-UT-2009-12-627.

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This thesis describes the generic modeling of a Doubly-Fed Induction Generator (DFIG) based wind turbine. The model can also represent a wind plant with a group of similar wind turbines lumped together. The model is represented as a controlled current source which injects the current needed by the grid to supply the demanded real and reactive power. The DFIG theory is explained in detail as is the rationale for representing it by a regulated current source. The complete model is then developed in the time-domain and phasor domain by the interconnection of various sub-systems, the functions of which have been described in detail. The performance of the model is then tested for steady-state and dynamic operation. The model developed can be used for bulk power system studies and transient stability analysis of the transmission system. This thesis uses as its basis a report written for NREL [1].
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Dhanuka, Raghav. "Modelling of doubly fed induction generator based wind turbine". Thesis, 2013. http://ethesis.nitrkl.ac.in/5343/1/109EE0268.pdf.

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There has been a constant rise in the use of renewable energy resources. Global wind energy capacity soared by a fifth to 238GW at the end of 2011. India being the 5th largest player globally, accounted for 16GW. Wind energy is an important form of renewable energy as there is no greenhousE gas emission compared to non-renewable fossil fuels. There has been a rising demand for wind energy ever since its first implementation. This project work studies the power-speed characteristics and the torque-speed characteristics and the fundamentals of wind electrical systems along with the modeling of the various wind turbine features and simulation of the same using MATLAB-SIMULINK. It deals with the vector control and modeling of the Doubly-Fed Induction Generator, which can be used to transmit power to the network through both the stator and the converters connected to the rotor. The turbine current, voltage, power and other characteristics are studied on variation of the grid parameters.

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Hwa, Shu Wen, i 許文華. "Frequency Regulation by Doubly Fed Induction Generator-based Wind Power Plants". Thesis, 2016. http://ndltd.ncl.edu.tw/handle/99342350982891570323.

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碩士
國立中正大學
電機工程研究所
104
The increasing wind penetration in today’s power grids has led to growing interest in the frequency control capabilities of wind generation. A doubly fed induction generator (DFIG)-based wind power plant naturally does not provide frequency response because of the decoupling between the output power and the grid frequency. Therefore, the control system in the DFIG needs to be modified to equip it with the capability to participate in regulating and restoring grid frequency during a disturbance. The main goal of this work is to develop a complex DFIG model with the modified control system in the DFIGs. The work utilized the power system analysis software PSCAD/EMTDC. Instead of the built-in component of PSCAD, this study applied detailed DFIG model to study the theory and control for the DFIG based wind turbine. In this study, the rotor-side converter and grid-side converter are controlled by the direct power control (DPC) and the voltage oriented control (VOC) methods, respectively. The additional control loops, including the inertia and droop loops, were added to the DFIG control system to provide transient frequency regulation. If a DFIG operates at the maximum power point tracking (MPPT) mode, it would lack power reserve margin. Therefore, a sub-optimal operating mode was applied to the DFIG control system in this study. The simulation results prove that the developed rotor-speed control system is helpful to improve the transient frequency stability. Finally, the effect of parameters of the modified control system in DFIGs on the frequency response has been investigated.

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Yu-HsiangWang i 王鈺翔. "Mitigation of Subsynchronous Resonance in Doubly-fed Induction Generator-Based Wind Farms". Thesis, 2015. http://ndltd.ncl.edu.tw/handle/r26wzh.

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Mahadanaarachchi, Viraj Pradeep. "Fault analysis and protection of doubly fed induction generator-based wind farms". 2009. http://digital.library.okstate.edu/etd/Mahadanaarachchi_okstate_0664M_10188.pdf.

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Pradhan, Prangya Parimita. "Robust Control Schemes for a Doubly Fed Induction Generator based Wind Energy Conversion System". Thesis, 2022. http://ethesis.nitrkl.ac.in/10344/1/2022_PhD_PPPradhan_514EE1009_Robust.pdf.

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Due to many advantages, such as variable speed operation, low noise, high torque, and ease of maintenance, the Doubly Fed Induction Generator (DFIG) is extensively employed in a Wind Energy Conversion System (WECS). To control a DFIG-based WECS, active power extraction from the wind must be regulated while reactive power must be kept at zero in order to ensure unity power factor operation. A number of control algorithms for controlling the active and reactive power of WECS have been proposed in the past. A WECS is encountered with several parametric uncertainties and external disturbances. Thus, it is essential to tackle the impact of parametric uncertainties and disturbances in the WECS characteristics by suitable design and implementation of appropriate robust control algorithms to achieve good performance. Controlling the active and reactive power of WECS has been the subject of a lot of research. Parametric uncertainties, on the other hand, have a substantial impact on the performance of active and reactive power regulation in a WECS. As a result, developing appropriate controllers for managing the active and reactive power of the WECS in the presence of parametric uncertainties and disturbances is regarded as a challenging control problem. The purpose of this dissertation is to develop robust control algorithms for a DFIG-based grid-connected WECS that can control both active and reactive power in the presence of parametric uncertainties and disturbances. As the active and reactive power of a DFIG are dependent, it becomes necessary to design suitable controller such as that the active and reactive power can be regulated separately by decoupling the active and reactive power control loops. The thesis starts with the development of a Proportional-Integral (PI) controller and Sliding Mode Controller (SMC) to control the active and reactive power of DFIG-based WECS that are delivered to the grid. The performance of PI and SMC controllers are evaluated under nominal conditions. An Autoregressive Moving Average with Exogenous (ARMAX) model is developed for DFIG-based WECS. This ARMAX model of the WECS is used to design a Model Predictive Control (MPC). By using the input-output values from previous sampling instants over a time horizon, the MPC predicts the system’s future output. The computing time, on the other hand, is a substantial barrier to MPC implementation. As a result, a variety of approaches have been used to lessen MPC’s computational load. To lessen the time complexity of the MPC problem, usually optimal solutions are adopted. A Linear Matrix Inequality (LMI) approach is used to reduce the computation time caused by the MPC. The optimization problem is solved using the LMI. PI is an excellent choice in the majority of industrial applications among all classical and current control methods. Because WECS has uncertainties due to intermittency in the wind speed various suitable feedback control mechanisms are necessary to address these concerns. An Extended State Observer (ESO) successfully estimates the unknown dynamics and disturbance. The rotor resistance and mutual inductance of the DFIG are modified to evaluate the robustness of the proposed MADRC. Peak overshoot and settling duration of the active power response are studied as a function of the aforementioned parameters. In the face of parametric uncertainty, the developed controller is found effective in managing the active and reactive power of DFIG, as well as rejecting external disturbance in desired value tracking. The proposed MADRC successfully handles parametric variation for set point tracking of active and reactive power of WECS, according to simulation and experimentation results. To improve the tracking accuracy of a DFIG-based WECS an online optimization approach based on wavelet neural networks for parameter adjustment of Active Disturbance Rejection Control (ADRC).

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23

Madeira, Tiago Caetano. "Model Predictive Control of a Doubly-fed Induction Generator, Connected to a Dc-grid, for Distributed Generation". Master's thesis, 2018. http://hdl.handle.net/10316/86728.

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Dissertação de Mestrado Integrado em Engenharia Electrotécnica e de Computadores apresentada à Faculdade de Ciências e Tecnologia
Esta dissertação apresenta uma estratégia de controlo preditivo aplicada a um gerador de indução duplamente alimentado (DFIG) ligado a uma rede dc, adequada para geração distribuída e em ambiente de micro-rede. A topologia de ligação da DFIG à rede dc é obtida através da substituição de um dos inversores de fonte de tensão por um retificador a díodos. Contudo a inclusão do retificador a díodos origina uma ondulação no binário, caracterizada por uma componente que oscila a uma frequência seis vezes superior à frequência do estator. Esta componente harmónica tem efeitos negativos sobre os componentes mecânicos do sistema, e como tal, são necessários esforços para eliminar essas oscilações no binário.As estratégias de controlo clássicas, baseadas na orientação de campo, abordam esta questão através da inclusão de controladores ressonantes, ou através da decomposição e supressão desta componente harmónica em referenciais múltiplos. No entanto, estes métodos apresentam desvantagens inerentes, tais como: grande esforço de sintonização, resposta dinâmica inferior e dificuldade de incluir restrições no sistema. Além disso, a existência de múltiplas malhas de controlo dita o uso de uma separação elevada nas larguras de banda do sistema de controlo e que a estabilidade do sistema está fortemente dependente da largura de banda da malha interna.A utilização de controlo preditivo baseado em modelos (MPC) no sistema de controlo proposto, consegue evitar todas as dificuldades associadas ao controlo vetorial, e é capaz de praticamente eliminar as oscilações de baixa frequência presentes no binário. Atendendo que as estratégias de controlo preditivo são baseadas em modelos discretos, o seu desempenho é fortemente dependente da precisão dos parâmetros do modelo, assim como da correcta estimação destes parâmetros. Por outro lado, a complexidade do modelo discreto deve também ser minimizada, por forma a tornar o algoritmo viável para uso prático. Como tal, também é fornecida uma comparação do desempenho do sistema, quando as diferentes técnicas de discretização são usadas, designadamente o método de Euler e a expansão em série de Taylor.
This work presents a predictive control strategy applied to a doubly-fed induction generator (DFIG) connected to a dc microgrid, suitable for distributed generation purposes and microgrid environment. The topology of connecting the DFIG to the dc grid consists in the replacement of one voltage source inverter by a diode rectifier. However, the inclusion of the diode rectifier gives rise to a large torque ripple, characterized by a component oscillating at six times the stator frequency. This harmonic component has negative effects on the mechanical components of the drive system and as such, efforts are needed to eliminate those torque oscillations.Classical control strategies, based on field orientation try to address this issue by the inclusion of resonant controllers, or by decomposing and suppressing this harmonic component in multiple reference frames. However, those methods have inherent disadvantages, such as: great tuning effort, inferior dynamic response and difficulty to include restrictions in the system. Furthermore, the existence of multiple control loops dictates that separate bandwidth for them must be ensured, as the stability of the system is closely related to the bandwidth of the inner loop. The use of model predictive control (MPC) in the proposed control system system avoids all the difficulties associated with vector control and is able to practically fully eliminate the low-frequency torque oscillations.Attending that predictive control strategies are based in discrete models, their performance is heavily dependent on the model parameters accuracy and of a correct parameter estimation. On the other hand, the complexity of the discrete model must also be minimized, to make the algorithm feasible for practical use. As such, a comparison is also provided on the steady-state and dynamic performance of the system, when the forward Euler and Taylor series expansion discretization methods are used.

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Reddy, Kota Vinay Kumar. "Modelling and Control of Doubly Fed Induction Generator Based Stand-Alone Wind Energy Conversion System". Thesis, 2015. http://ethesis.nitrkl.ac.in/7835/1/2015_MT_Modelling_Reddy.pdf.

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The application of wound rotor induction machine is widely spread in wind energy generating stations because of its adaptability for variable speed wind turbines through which maximum possible extraction of wind energy is possible. Also among all the induction generator configurations for wind power systems the use of Doubly Fed Induction Generator (DFIG) configuration with back to back pulse width modulated voltage source converters (VSC) is one of the best topologies available and it is suitable for both grid connected systems as well as stand-alone systems. Here only stand-alone application of DFIG is considered. In this thesis mathematical modelling of doubly fed induction machine is presented. The control strategies for both stator side converter and rotor side converter are developed in stator flux oriented reference frame. The dynamics of dc link voltage build-up phase is also included. The stator side converter is used to control the output voltage in direct voltage control manner and the rotor side converter is current controlled where the power imbalance of the system is nullified using dc link voltage controller which modifies the quadrature axis rotor current reference value according to the changes in the wind speed as well as the load. Two control algorithms are presented out of which one gives the best performance for all kinds of loads (balance, unbalance, linear and non-linear) and the other gives poor load regulation and unwanted distortions in the output voltage for non-linear and unbalanced loads

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25

"Power system dynamic enhancement using phase imbalance series capacitive compensation and doubly fed induction generator-based wind farms". Thesis, 2013. http://hdl.handle.net/10388/ETD-2013-04-1008.

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ABSTRACT Wind energy is among the fastest growing renewable energy technologies in the world that has been increasing by about 30% a year globally. Wind energy has proven to be a clean, abundant and completely renewable source of energy. Owing to the rapidly increasing use of wind power, the aspect of integrating high level of penetrations wind power into the grid is becoming more and more of reality. Examples of large wind farms in the United States are the 781.5 MW Roscoe wind farm in Texas, the 735.5 MW Horse Hollow Wind Energy Center in Taylor and Nolan County, Texas, the 845 MW Shepherds Flat wind farm in Oregon and the 1550 MW Alta wind farm being developed in California. As most large wind farms in North America employ Doubly-fed Induction Generator (DFIG) wind turbines, their voltage-sourced converter-based back-to-backs offer independent control of the real and reactive power. The use of these control capabilities have been recently proposed for damping power swings, inter-area oscillations as well as subsynchronous resonance. There is, however, a question that is always associated with the use of voltage-sourced converter -based back-to-back wind farms for damping power system oscillations: what happens when there is no wind? The keyword to the answer is “combined”. The potential benefit of using these types of wind farms for damping power system oscillations should always be combined with conventional damping devices (power system stabilizers, thyristor controlled series capacitor, static synchronous series compensator, high voltage dc systems, etc.). This thesis reports the results of digital time-domain simulation studies that are carried out to investigate the potential use of supplemental controls of DFIG-based wind farms combined with a phase imbalanced hybrid series capacitive compensation scheme for damping power system oscillations. The thesis also addresses the recent concern over the case of large share of wind power generation which results in reducing the total inertia of the synchronous generators and degrading the system transient stability. In this regards, the results of the investigations have shown that in such a case; properly designed supplemental controllers for the wind farm converters could be an asset in improving the system transient stability rather than degrading it. Time-domain simulations are conducted on a benchmark model using the ElectroMagnetic Transients program (EMTP-RV).

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"Simultaneous mitigation of subsynchronous resonance and subsynchronous interaction using offshore and doubly-fed induction generator-based wind farms". Thesis, 2014. http://hdl.handle.net/10388/ETD-2014-07-1636.

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Subsynchronous resonance (SSR) is one of the major obstacles for the wide spread of high degrees (60% and higher) of series capacitor compensation. Recently, a new obstacle, namely Subsynchronous Interaction (SSI) has been added to the list after the Zorillo Gulf wind farm incident in Texas in October 2009. SSI is due to the interaction between large Doubly Fed Induction Generator (DFIG)-based wind farms and series capacitor compensated transmission systems. In integrated power systems incorporating series capacitor compensated transmission lines and high penetration of wind energy conversion systems, especially DFIG-based wind farms, SSR and SSI could occur concurrently as a result of some system contingences. Therefore, mitigating SSR and SSI is an important area of research and development targeting at developing practical and effective countermeasures. This thesis reports the results of digital time-domain simulation studies that are carried out to investigate the potential use of offshore and DFIG-based wind farms for simultaneous mitigation of SSR and SSI. This is achieved through introducing supplemental control signals in the reactive power control loops of the grid side converters of the DFIG wind turbines or the HVDC onshore Modular Multilevel Converter (MMC) connecting the offshore wind farm to the grid. In this context, two supplemental controls designated as Supplemental Controls I and II are examined. Supplemental Control I introduces a signal in the HVDC onshore converter to damp both SSR and SSI oscillations. On the other hand, Supplemental Control II introduces a signal in the HVDC onshore converter for damping SSR oscillations and another signal in the grid side converters of the DFIG wind turbines for damping SSI oscillations. Time-domain simulations are conducted on a benchmark model using the ElectroMagnetic Transients program (EMTP-RV). The results of the investigations have demonstrated that the presented two supplemental controls are very effective in mitigating the SSR and SSI phenomena at different system contingencies and operating conditions.

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Ogeti, Pedda Suresh. "Robust Active and Reactive Power Control Schemes for a Doubly Fed Induction Generator Based Wind Energy Conversion System". Thesis, 2016. http://ethesis.nitrkl.ac.in/8207/1/thesis_NOV_2016_-510EE809.pdf.

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In view of resolving rising environmental concern arising out of fossil fuel based power generation, more electricity has to be generated from renewable energy sources. Out of the several renewable energy options available today, wind energy is considered to be the most promising one due to its high energy conversion efficiency compared to one of its competitors, i.e. the solar photovoltaic system. Now-a-days, large wind farms are generating thousands of megawatts of power feeding to the grid. In literature, number of controllers such as conventional proportional integral (PI) control, linear parameter varying (LPV) control, gain scheduling control, robust control, model predictive control have been proposed for both torque and pitch control. In these controllers, some of the important issues such as robustness for nonlinear dynamics of wind turbine and stability are not considered simultaneously. Hence, it is necessary to design appropriate controllers for extracting maximum power from the wind turbine whilst the robustness and stability of the Wind Energy Conversion System (WECS) are ensured. Hence, in this thesis, firstly the focus is made to design control system for the wind turbine coupled with the DFIG (torque and pitch control) using one of the very promising robust control paradigm called sliding mode controller for achieving robustness, reducing chattering phenomenon and stability of the WECS. Since the number of terms in control inputs (i.e. torque and pitch angle) and outputs (i.e. DFIG output power and speed) are more in wind control dynamics, selection of significant terms is important for reducing the complexity of controlling. Therefore, a Nonlinear Autoregressive Moving Average with exogenous input (NARMAX) model of the WECS has been developed. The parameters of this NARMAX model are estimated by suitably designing an on-line adaptive Recursive Least squares (RLS) algorithm. Subsequently for controlling speed and achieving efficient power regulation of the WECS a nonlinear model predictive controller (NAMPC) has been developed in which the control variables (torque and pitch) are optimised by formulating a cost function. Subsequently for the WECS, the power converters connecting the DFIG to the grid have been designed. For controlling stator active and reactive power of DFIG connected to the grid, a state feedback controller for the DFIG has been developed using a linear quadratic optimal theory with preview concept. This Linear Quadratic Regulator Optimal Preview Control (LQROPC) scheme is employed with a stator voltage oriented control (SVOC) technique. This Optimal preview control is used to solve the tracking and rejection problems with an assumption that the signals to be tracked or rejected are available a priori by a certain amount of time. Even though the OPC provides very good tracking and disturbance suppression performance, but it is sensitive to the DFIG circuit parameters which makes the WECS system unstable. Hence, to address the parameter uncertainty of the DFIG, a sliding mode controller has been proposed and the robustness of the WECS have been verified by using the Lyapunov criterion. Then, a 2 kW DFIG based WECS experimental setup has been developed in the laboratory to study the effectiveness of the controllers developed.

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"SIMULTANEOUS MITIGATION OF SUBSYNCHRONOUS RESONANCE AND SUBSYNCHRONOUS INTERACTION USING FULL-SCALE FREQUENCY CONVERTER- AND DOUBLY-FED INDUCTION GENERATOR-BASED WIND FARMS". Thesis, 2014. http://hdl.handle.net/10388/ETD-2014-05-1551.

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Subsynchronous Resonance (SSR) is one of the major obstacles for the wide spread of high degrees (60% and higher) of series capacitor compensation. Recently, a new obstacle, namely Subsynchronous Interaction (SSI) has been added to the list after the Zorillo Gulf wind farm incident in Texas in October 2009. SSI is due to the interaction between large Doubly-Fed Induction Generator (DFIG)-based wind farms and series capacitor compensated transmission systems. In integrated power systems incorporating series capacitor compensated transmission lines and high penetration of wind energy conversion systems, especially DFIG-based wind farms, SSR and SSI could occur concurrently as a result of some system contingences. Therefore, mitigating SSR and SSI is an important area of research and development targeting at developing practical and effective countermeasures. This thesis reports the results of digital time-domain simulation studies that are carried out to investigate the potential use of Full-Scale Frequency Converter (FFC) and DFIG-based wind farms for simultaneous mitigation of SSR and SSI. This is achieved through introducing supplemental control signals in the reactive power control loops of the grid side converters of the DFIG and/or the FFC wind turbines. In this context, two supplemental controls designated as Supplemental Controls 1 and 2 are examined. Supplemental Control 1 introduces a signal in the grid side converter of the FFC wind turbines to damp both SSR and SSI oscillations. On the other hand, Supplemental Control 2 introduces a signal in the grid side converter of the FFC wind turbines for damping SSR oscillations and another signal in the grid side converters of the DFIG wind turbines for damping SSI oscillations. Time-domain simulations are conducted on a benchmark model using the ElectroMagnetic Transients program (EMTP-RV). The results of the investigations have demonstrated that the presented two supplemental controls are very effective in mitigating the SSR and SSI phenomena at different system contingencies and operating conditions.

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Gatavi, Ehsan. "Voltage regulation and reactive power compensation to improve low voltage ride-through capability for doubly fed induction generator-based wind turbine". Thesis, 2019. http://hdl.handle.net/1959.7/uws:54766.

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Of all the renewable energies, wind power is proliferating and it now plays a significant part in the power supply. The system known as Doubly Fed Induction Generator (DFIG) is the most popular wind turbine, because it plays a very significant role in enhancing low voltage ride through (LVRT) capability. Ancillary services such as voltage control and reactive power capability are the main concerns in wind power control systems and need to be managed in detail and with great care. The lack of reactive power during a fault period can result in instability in generators and/or disconnection of a wind turbine from the power system. The main aim of this study is to explain and describe the most effective and efficient approaches for improving the stability and reliability of wind power plants. This theme is closely associated with LVRT capability enhancement. Wind farms are regarded as large-scale power plants with interconnected systems, where all systems interact with each other to improve the efficiency of the plant and thus the quality of the output power. However, the conventional centralized controller is inappropriate for such plants. Also, not many studies have paid attention to this fact due to strong nonlinear behavior of such plants. Accordingly, a new control strategy is presented in Chapter 3 based on employing MPC and incorporating the voltage and current constraints. LVRT capability is extended by adding a series of dynamic breaking resistors to deal with severe faults and to short circuit the RSC. In Chapter 4, an asymptotic model of a wind farm equipped with DFIG is given with a description of the outcomes of interconnections. The LVRT capability is improved by introducing a class of plant-wise controller for a decentralized system. This is done by taking care of voltage at an individual point of common coupling (PCC) and controlling the DFIG active and reactive power, separately. Further, a new reactive power control strategy for voltage stability and improvement of LVRT capability is presented in Chapter 5. Both RSC and GSC are taken into account for the purpose of voltage stability and improvement of systems robustness. In the algorithm developed, the required reactive power is optimally managed at an individual point of common coupling (PCC) by using linear matrix inequality (LMI) technique. JR has also been employed to have better accuracy and realize the required bound of injected reactive power. To minimize the systems conservative nature, dynamic couplings of the system are considered, unlike the existing methods. This research aims to address these shortcomings using novel methodologies. By identifying the drawbacks of existing LVRT solutions, the study specifically focuses on addressing three problems to regulate the voltage at individual points of common coupling. The objective is to maximize the DFIG output reactive power concerning the stability of the entire large- scale wind power plant by designing multiple local controllers. To sum up, the key contribution of the study is to design a control strategy that gives DFIG the ability to full the two main grid code requirements in one inclusive approach, while other existing proposals treat each requirement as a separated issue. To demonstrate the effectiveness of all approaches presented in this the- sis, MATLAB software is used for simulation. After all, the results have been demonstrated the flexibility of model predictive control technology and motivated numerous novel works and researches to address practical problems in the field of the wind power industry.

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"Impact of Increased Penetration of DFIG Based Wind Turbine Generators on Rotor Angle Stability of Power Systems". Doctoral diss., 2010. http://hdl.handle.net/2286/R.I.8742.

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abstract: An advantage of doubly fed induction generators (DFIGs) as compared to conventional fixed speed wind turbine generators is higher efficiency. This higher efficiency is achieved due to the ability of the DFIG to operate near its optimal turbine efficiency over a wider range of wind speeds through variable speed operation. This is achieved through the application of a back-to-back converter that tightly controls the rotor current and allows for asynchronous operation. In doing so, however, the power electronic converter effectively decouples the inertia of the turbine from the system. Hence, with the increase in penetration of DFIG based wind farms, the effective inertia of the system will be reduced. With this assertion, the present study is aimed at identifying the systematic approach to pinpoint the impact of increased penetration of DFIGs on a large realistic system. The techniques proposed in this work are tested on a large test system representing the Midwestern portion of the U.S. Interconnection. The electromechanical modes that are both detrimentally and beneficially affected by the change in inertia are identified. The combination of small-signal stability analysis coupled with the large disturbance analysis of exciting the mode identified is found to provide a detailed picture of the impact on the system. The work is extended to develop suitable control strategies to mitigate the impact of significant DFIG penetration on a large power system. Supplementary control is developed for the DFIG power converters such that the effective inertia contributed by these wind generators to the system is increased. Results obtained on the large realistic power system indicate that the frequency nadir following a large power impact is effectively improved with the proposed control strategy. The proposed control is also validated against sudden wind speed changes in the form of wind gusts and wind ramps. The beneficial impact in terms of damping power system oscillations is observed, which is validated by eigenvalue analysis. Another control mechanism is developed aiming at designing the power system stabilizer (PSS) for a DFIG similar to the PSS of synchronous machines. Although both the supplementary control strategies serve the purpose of improving the damping of the mode with detrimental impact, better damping performance is observed when the DFIG is equipped with both the controllers.
Dissertation/Thesis
Ph.D. Electrical Engineering 2010

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