Rozprawy doktorskie na temat „DFIG MODEL”

The objective of this dissertation is to carry out dynamic modeling, analysis and control of power systems with Renewable Energy Sources (RES) such as: Photovoltaic (PV) power sources and wind farms. The dissertation work is mainly focused on microgrid since it plays a major role in modern power systems and tend to have higher renewable power penetration. Two main theoretical concepts, dynamic phasor and impedance modeling have been adopted to model and analyze the power systems/mocrogrids with RES. The initial state calculation which is essential for small signal analysis of a system is carried out as the first step of the dissertation work. Dynamic phasor and impedance modeling techniques have been utilized to model and analyze power systems/micogrids as the second phase of the work. This part consists of two main studies. First case investigates the impedance modeling of Thyristor Controller Series Capacitor (TCSC) for sub-synchronous resonance (SSR) analysis where a wind farm is connected to a power system through series compensated line. Second case utilizes the dynamic phasor concept to model a microgrid in unbalanced condition. Here the unbalance is caused by a single phase PV connected to the microgrid. Third Phase of the dissertation work includes upper level control of the microgrid. Here prediction and optimization control for a microgrid with a wind farm, a PV system, an energy storage system and loads is evaluated. The last part of the dissertation work focuses on real time modeling and hardware in loop simulation test bed for microgrid applications. This dissertation has led to four journal papers (three accepted, one submitted) and five conference papers.

Quang Ninh province, Vietnam has a rich wind power resources. This type of energy will be soon utilized for generating power to supply all industrial sites including mining corporations. Because of geological characteristics, wind power stations are located near the 6kV grid of mining areas, therefore it needs to make the analysis about the connection ability of wind power generators to the grids. The paper presents the connection model of a wind turbine and 6kV grids. Based on this model, the simulations of system’s possible operating mode are implemented. The conclusions about the suitable operating modes of wind turbine are pointed out to give the operators and grid managers a general observation for the possibility of connecting a wind turbine to 6kV grid
Tỉnh Quảng Ninh là một trong những địa phương giàu tiềm năng về năng lượng gió. Theo phân tích, loại năng lượng này sẽ sớm được đưa vào cung cấp điện năng cho các khu công nghiệp trong đó có các công ty than. Do đặc thù địa lý, các trạm phát phong năng được đặt khá gần các lưới điện 6kV của mỏ, vì thế cần tiến hành phân tích khả năng kết nối trực tiếp các máy phát điện gió với lưới điện này. Bài báo giới thiệu mô hình kết nối máy phát điện gió với lưới 6kV. Các mô phỏng về các chế độ vận hành có thể có của lưới cũng được thực hiện. Các kết luận về chế độ vận hành thích hợp của tua bin gió được đúc rút để giúp người vận hành, các nhà quản lý lưới điện có được cái nhìn tổng quan về khả năng kết nối tua bin gió với lưới điện 6kV.

Cette thèse vise à élaborer de nouvelles stratégies de commande basées sur la commande prédictive pour le système de génération d’énergie éolienne. La topologie des systèmes de production éolienne basées sur le Générateur Asynchrone à Double Alimentation (GADA) qui convient à des plateformes de génération dans la gamme de puissance de 1.5 à 6 MW est abordée. Du point de vue technologique, le convertisseur à trois niveaux et clampé par le neutre (3L-NPC) est considéré comme une bonne solution pour une puissance élevée en raison de ses avantages: capacité à réduire la distorsion harmonique de la tension de sortie et du courant, et augmentation de la capacité du convertisseur grâce à une tension réduite appliquée à chaque semi-conducteur de puissance. Une description détaillée de la commande prédictive à ensemble de commande fini (FCS-MPC) avec un horizon de prédiction de deux pas est présentée pour deux boucles de régulation: celle liée au convertisseur connecté au réseau et celle du convertisseur connecté au GADA. Le principe de la commande repose sur l’utilisation d’un modèle de prédiction permettant de prédire le comportement du système pour chaque état de commutation du convertisseur. La minimisation d’une fonction de coût appropriée prédéfinie permet d’obtenir la commutation optimale à appliquer au convertisseur. La thèse étudie premièrement les problèmes liées à la compensation du temps de calcul de la commande et au choix et aux pondérations de la fonction de coût. Ensuite, le problème de stabilité de la commande FCS-MPC est abordé en considérant une fonction de Lyapunov dans la minimisation de la fonction de coût. Finalement, une étude sur la compensation des effets des temps morts du convertisseur est présentée
This thesis aims to elaborate new control strategies based on Model Predictive control for wind energy generation system. We addressed the topology of doubly fed induction generator (DFIG) based wind generation systems which is suitable for generation platform power in the range in 1.5-6 MW. Furthermore, from the technological point of view, the three-level neutral-point clamped (3L-NPC) inverter configuration is considered a good solution for high power due to its advantages: capability to reduce the harmonic distortion of the output voltage and current, and increase the capacity of the converter thanks to a decreased voltage applied to each power semiconductor.In this thesis, we presented a detailed description of finite control set model predictive control (FCS-MPC) with two step horizon for two control schemes: grid and DFIG connected 3L-NPC inverter. The principle of the proposed control scheme is to use system model to predict the behaviour of the system for every switching states of the inverter. Then, the optimal switching state that minimizes an appropriate predefined cost function is selected and applied directly to the inverter.The study of issues such as delay compensation, computational burden and selection of weighting factor are also addressed in this thesis. In addition, the stability problem of FCS-MPC is solved by considering the control Lyapunov function in the design procedure. The latter study is focused on the compensation of dead-time effect of power converter

Depuis une dizaine d'année, l'évolution des machines de calcul tend vers des architectures parallèles et hétérogènes. Composées de plusieurs nœuds connectés via un réseau incluant chacun des unités de traitement hétérogènes, ces grilles offrent de grandes performances. Pour programmer ces architectures, l'utilisateur doit s'appuyer sur des modèles de programmation comme MPI, OpenMP, CUDA. Toutefois, il est toujours difficile d'obtenir à la fois une bonne productivité du programmeur, qui passe par une abstraction des spécificités de l'architecture et performances. Dans cette thèse, nous proposons d'exploiter l'idée qu'un modèle de programmation spécifique à un domaine applicatif particulier permet de concilier ces deux objectifs antagonistes. En effet, en caractérisant une famille d'applications, il est possible d'identifier des abstractions de haut niveau permettant de les modéliser. Nous proposons deux modèles spécifiques au traitement du signal et de l'image sur cluster hétérogène. Le premier modèle est statique. Nous lui apportons une fonctionnalité de migration de tâches. Le second est dynamique, basé sur le support exécutif StarPU. Les deux modèles offrent d'une part un haut niveau d'abstraction en modélisant les applications de traitement du signal et de l'image sous forme de graphe de flot de données et d'autre part, ils permettent d'exploiter efficacement les différents niveaux de parallélisme tâche, données, graphe. Ces deux modèles sont validés par plusieurs implémentations et comparaisons incluant deux applications de traitement de l'image du monde réel sur cluster CPU-GPU
Since a decade, computing systems evolved to parallel and heterogeneous architectures. Composed of several nodes connected via a network and including heterogeneous processing units, clusters achieve high performances. To program these architectures, the user must rely on programming models such as MPI, OpenMP or CUDA. However, it is still difficult to conciliate productivity provided by abstracting the architectural specificities, and performances. In this thesis, we exploit the idea that a programming model specific to a particular domain of application can achieve these antagonist goals. In fact, by characterizing a family of application, it is possible to identify high level abstractions to efficiently model them. We propose two models specific to the implementation of signal and image processing applications on heterogeneous clusters. The first model is static. We enrich it with a task migration feature. The second model is dynamic, based on the StarPU runtime. Both models offer firstly a high level of abstraction by modeling image and signal applications as a data flow graph and secondly they efficiently exploit task, data and graph parallelisms. We validate these models with different implementations and comparisons including two real-world applications of images processing on a CPU-GPU cluster

O ChipCflow é o projeto de uma ferramenta para execução de algoritmos utilizando o modelo a fluxo de dados dinâmico em hardware reconfigurável. Tem como principal objetivo utilizar o modelo de arquitetura a fluxo de dados, associado ao conceito de arquiteturas reconfiguráveis, para acelerar programas de aplicação escritos em C. Essa aceleração vai acontecer nas partes mais intensas de processamento (exemplo: loops), através da execução direta em hardware, aproveitando ao máximo o paralelismo considerado natural do modelo a fluxo de dados. O módulo de conversão C em grafo a fluxo de dados, desenvolvido neste trabalho de doutoramento, é parte fundamental no desenvolvimento do projeto ChipCflow e se trata de um pré-compilador C que gera código VHDL para os operadores a fluxo de dados a partir de módulos do programa de aplicação escrito originalmente em C. É possível considerar como principal resultado dessa tese, a implementação de algoritmos a partir de uma linguagem C em grafo a fluxo de dados no modelo proposto no projeto ChipCflow, onde os operadores a fluxo de dados são os já tradicionalmente conhecidos, e até mesmo a forma de interconexão também, entretanto a forma de abordar essa implementação, em VHDL, e na forma de fluxo de dados dinâmico, torna o modelo proposto, tanto para o hardware como para o compilador, uma característica única existente até o momento.
ChipCflow is a tool for algorithms execution using a data dynamic flow in reconfigurable hardware. The main purpose of the work is to use the data flow architecture model, associated to the concept of reconfigurable architectures, to speed up C written applications. The program acceleration happens in the most intensive processing parts (example: loops), through direct hardware execution, using to advantage of the natural parallelism of the data flow model. The C conversion module in data flow graph is the basic part in the development of the ChipCflow project and the specific objective of the developed work. In this work we present detais of the C precompiler that generates VHDL code for the data flow operators modules of the written program of the original application in C. It is possible to consider as the main result of this thesis, the implementation of algorithms from a C language in the data flow graph model proposed in the project ChipCflow, where the operators to the data stream are typically already known, and even the way interconnection too, but how to approach the implementation in VHDL, and as a dynamic data flow, makes the proposed model for both the hardware and the compiler, a feature only available so far.

Le travail de cette thèse apporte une contribution aux méthodes de réglage de la tension dans les réseaux électriques. Il s’agit de fournir au réseau la puissance active et surtout la puissance réactive nécessaire pour réguler la tension et aboutir à un système équilibré vue du côté source. Ces puissances sont extraites d’une source d’energie renouvelable : une attention particulière a été portée à l’énergie éolienne raccordée au réseau à travers la Machine Asynchrone à Double Alimentation (MADA) pilotée par des convertisseurs statiques. Le système de contrôle le plus répandu des éoliennes est basé principalement sur la technique d’extraction du maximum de puissance. Cependant, cette technique limite la mise en oeuvre deservices auxiliaires, telle que la participation des éoliennes au réglage de la tension dans le réseau électrique. Pour cela, une nouvelle méthode d’extraction du coefficient de puissance optimal, permettant d’améliorer la participation de la MADA à la régulation de la tension dans le réseau (compensation de la puissance réactive et du déséquilibre), a été développée. Le convertisseur multiniveaux à structure NPC (Neutral Point Clamped) raccordant l’énergie renouvelable au réseau a été étudié. La commande prédictive assurant simulatnément l’amélioration du facteur de puissance, l’équilibrage du réseau électrique et du bus continu du convertisseur NPC a été proposée. Ensuite, l’application de cette commande prédictive a été elargie en lui attribuant plusieurs objectifs : amélioration du facteur de puissance avec équilibrage du réseau, équilibrage du bus continu, minimisation des pertes par commutation et réduction de la tension de mode commun. La minimisation des pertes a été obtenue en proposant une nouvelle stratégie qui consiste à exploiter les datasheets constructeurs donnant l’évolution de l’énergie dissipée durant la commutation en fonction du courant. Ces courbes expérimentales ont été transformées en modèlesmathématiques implémentés dans la commande prédictive. Les résultats de simulation et expérimentaux sont présentés pour évaluer les performances de la méthode proposée
The work in this research thesis presents a contribution to voltage regulation in electrical networks. By considering adequate active and reactive powers injection into the grid, voltage control and load balancing are provided. These powers are generated from a grid connected renewable energy conversion system : a special attention was paid to the Wind Energy ConversionSystem (WECS) based on Doubly-Fed Induction Generator (DFIG).The typical control strategy for WECS is the maximum power coefficient tracking method. However, this method limits desirable ancillary power services, such as the participation of wind turbines in voltage regulation in the power grid. Therefore, a new method that derives the optimal power coefficient enhancing the participation of WTS in voltage regulation in the network (reactive and unbalanced power compensation), has been developed. The multilevel NPC (Neutral Point Clamped) converter, used for grid interface connection of renewable energy sources systems, has been studied. A predictive control method for the three-level NPC converter, capable of simultaneously compensating the problems of : DC link capacitors voltage balancing, load balancing and power factor correction in the power system, has been proposed. Then, the application of this predictive control was extended to simultaneously achieve multiple objectives: load balancing with power factor correction in the network, DC link capacitors voltage balancing, switching losses minimization and common mode voltage reduction. The switching losses minimization was obtained by proposing a new strategy which consists on exploiting the manufacturer datasheets that gives the evolution of the switching loss energy in function of the circulating current. The experimental curves of the datasheet are expressed in a mathematical model implemented in the predictive control. Simulation and experimental results are presented to evaluate the performance of the proposed method

Cette étude cherche à évaluer le Débit de la Filtration Glomérulaire (DFG) dans le rein humain par IRM. L'estimation de ce paramètre quantitatif nécessite le suivi de la cinétique intrarénale de Gd après son injection en bolus. Pour atteindre cet objectif, nous avons développé sous IDEA Siemens une séquence SR-FLASH strictement pondérée en T1 capable de suivre en dynamique l'évolution du signal RMN après l'injection d'un bolus de produit de contraste. Cette séquence possède un codage de phase centré permettant de déterminer le contraste au début de la période d'acquisition de l'image. Nous avons également mis en oeuvre une séquence d'inversion IR-FLASH (avec codage de phase centré) permettant la mesure de la relaxation longitudinale en l'absence de produit de contraste, ce paramètre étant indispensable à la conversion de l'intensité du signal en concentration. Sachant que la relation entre l'intensité du signal RMN et la concentration de Gd n'est pas linéaire, nous avons proposé deux méthodes originales et malgré tout rapides et robustes pour convertir le signal RMN en concentration locale de Gd. Ceci nous a permis d'évaluer l'évolution de la concentration dans les deux reins et dans l'aorte au cours des premiers passages du produit. L'ajustement des ces mesures de concentration sur les équations décrivant une modélisation bicompartimentale de la fonction rénale a permis de calculer le DFG de chaque rein dans une population de cinq sujets possédant un fonctionnement rénal normal
This study seeks to assess the Glomerular Filtration Rate (GFR) in the human kidney by MRI. To quantitatively estimate this parameter requires monitoring of the intrarenal kinetics of Gd after its bolus injection. To achieve this goal, we have developed under IDEA Siemens a SR-FLASH T1-weighted MRI sequence which can follow dynamic NMR signal changes after a bolus injection of Gd. This sequence has a centric phase-encoding scheme, and thus the image contrast was determined at the beginning of the acquisition period. Subsequently, we have implemented an IR-FLASH (with centric phase-encoding scheme) sequence to measure the longitudinal relaxation time in the absence of any injection of Gd ; this parameter is required to convert NMR signal intensities into Gd concentrations. knowing that the relation between the NMR signal intensities and the Gd concentrations is not linear, we have proposed two novel methods and yet fast and robust for conversion of the NMR signal intensities into local Gd concentration. This allowed us to estimate the temporal evolution of Gd concentrations in both kidneys and aorta. The fit of these concentrations measurements by a two-compartments model describing the function of the kidney allowed us to calculate the GFR of each kidney in a population of five subjects with normal renal function

Development Finance Institutions (DFIs) have played a crucial role in moving socially responsibility considerations up on the private equity industry’s agenda. DFIs add a development impact criterion to traditional financial performance goals in the investment industry and play a catalytic role by mobilizing other investors. The gap in research regarding DFIs implications and significance in the investment community from a SRI perspective is evident. The development impact objective introduced by the DFIs is examined to understand its effects on fund managers’ decision-making and if it exists a trade-off between this objective and financial performance. An understanding of how DFIs control fund managers to act in accordance to their objective as well as how they determine compensation schemes to incentivize them to pursue high return on investments, is discussed in relation to the agency theory. Furthermore, stakeholder/shareholder consideration is examined in relation to the subject. The aim of this study is to examine how the behavior of fund managers is affected by the involvement of a DFI investor and try to add to the understanding of their significance as institutional investors in developing markets. Previous studies have been more focused on determining the financial performance of socially responsible investments by using very similar quantitative data collection methods. This thesis undertakes an in-depth approach with the purpose to understand the fund manager’s drives as well as how a DFI involvement affects the behavior and decision-making process.   This thesis undertook a qualitative research strategy and semi-structured interviews were used as the tool to understand the fund managers’ personals beliefs and perceptions of how the relationship with DFIs affect them. The selection criteria for the fund managers was that they needed to work in a fund in which a DFIs has invested. We also included DFI investors in order to understand their point of view. The interview was recorded, transcribed and later divided into themes in accordance with the thematic approach, following six steps. Our findings show that Development Finance Institutions plays an important role in emerging markets and affect fund manager behavior to a certain extent. They did not perceive a trade-off between financial performance goals and development impact objectives. We conclude that DFIs increase fund manager focus on ESG/SEE elements in the investment process. DFIs requirements and reporting obligations is used as a tool to ensure that the fund manager act in accordance to DFI objective. The fund managers were neither willing to sacrifice commercial return in favor of development impact. Lastly, the interest among the DFIs and commercial investors is fairly similar, hence reducing the conflict of interest between investors.

AC motors are largely used in a wide range of modern systems, from household appliances to automated industry applications such as: ventilations systems, fans, pumps, conveyors and machine tool drives. Inverters are widely used in industrial and commercial applications due to the growing need for speed control in ASD systems. Fast switching transients and the common mode voltage, in interaction with parasitic capacitive couplings, may cause many unwanted problems in the ASD applications. These include shaft voltage and leakage currents. One of the inherent characteristics of Pulse Width Modulation (PWM) techniques is the generation of the common mode voltage, which is defined as the voltage between the electrical neutral of the inverter output and the ground. Shaft voltage can cause bearing currents when it exceeds the amount of breakdown voltage level of the thin lubricant film between the inner and outer rings of the bearing. This phenomenon is the main reason for early bearing failures. A rapid development in power switches technology has lead to a drastic decrement of switching rise and fall times. Because there is considerable capacitance between the stator windings and the frame, there can be a significant capacitive current (ground current escaping to earth through stray capacitors inside a motor) if the common mode voltage has high frequency components. This current leads to noises and Electromagnetic Interferences (EMI) issues in motor drive systems. These problems have been dealt with using a variety of methods which have been reported in the literature. However, cost and maintenance issues have prevented these methods from being widely accepted. Extra cost or rating of the inverter switches is usually the price to pay for such approaches. Thus, the determination of cost-effective techniques for shaft and common mode voltage reduction in ASD systems, with the focus on the first step of the design process, is the targeted scope of this thesis. An introduction to this research – including a description of the research problem, the literature review and an account of the research progress linking the research papers – is presented in Chapter 1. Electrical power generation from renewable energy sources, such as wind energy systems, has become a crucial issue because of environmental problems and a predicted future shortage of traditional energy sources. Thus, Chapter 2 focuses on the shaft voltage analysis of stator-fed induction generators (IG) and Doubly Fed Induction Generators DFIGs in wind turbine applications. This shaft voltage analysis includes: topologies, high frequency modelling, calculation and mitigation techniques. A back-to-back AC-DC-AC converter is investigated in terms of shaft voltage generation in a DFIG. Different topologies of LC filter placement are analysed in an effort to eliminate the shaft voltage. Different capacitive couplings exist in the motor/generator structure and any change in design parameters affects the capacitive couplings. Thus, an appropriate design for AC motors should lead to the smallest possible shaft voltage. Calculation of the shaft voltage based on different capacitive couplings, and an investigation of the effects of different design parameters are discussed in Chapter 3. This is achieved through 2-D and 3-D finite element simulation and experimental analysis. End-winding parameters of the motor are also effective factors in the calculation of the shaft voltage and have not been taken into account in previous reported studies. Calculation of the end-winding capacitances is rather complex because of the diversity of end winding shapes and the complexity of their geometry. A comprehensive analysis of these capacitances has been carried out with 3-D finite element simulations and experimental studies to determine their effective design parameters. These are documented in Chapter 4. Results of this analysis show that, by choosing appropriate design parameters, it is possible to decrease the shaft voltage and resultant bearing current in the primary stage of generator/motor design without using any additional active and passive filter-based techniques. The common mode voltage is defined by a switching pattern and, by using the appropriate pattern; the common mode voltage level can be controlled. Therefore, any PWM pattern which eliminates or minimizes the common mode voltage will be an effective shaft voltage reduction technique. Thus, common mode voltage reduction of a three-phase AC motor supplied with a single-phase diode rectifier is the focus of Chapter 5. The proposed strategy is mainly based on proper utilization of the zero vectors. Multilevel inverters are also used in ASD systems which have more voltage levels and switching states, and can provide more possibilities to reduce common mode voltage. A description of common mode voltage of multilevel inverters is investigated in Chapter 6. Chapter 7 investigates the elimination techniques of the shaft voltage in a DFIG based on the methods presented in the literature by the use of simulation results. However, it could be shown that every solution to reduce the shaft voltage in DFIG systems has its own characteristics, and these have to be taken into account in determining the most effective strategy. Calculation of the capacitive coupling and electric fields between the outer and inner races and the balls at different motor speeds in symmetrical and asymmetrical shaft and balls positions is discussed in Chapter 8. The analysis is carried out using finite element simulations to determine the conditions which will increase the probability of high rates of bearing failure due to current discharges through the balls and races.

Wind energy stands out among other renewable coffers or energy sources (RESs), analogousto solar, wave, and geothermal energy due to its highest level of safety and low cost among all other types of renewable resources. There were no precise guidelines demonstrated to concatenate the wind dynamic networks to the grid or any other load in the early eras when sharing wind energy with the grids was relatively low and inconsequential. It was then advised to disconnect the wind turbine from the grid and any other connected power electronic converters in the event of any sudden abrupt disturbance or speed change in the system. However, DFIG is presently often times employed in wind turbines because it is protean and adaptive to the sudden or abrupt wind. DFIG model is modeled in the dissertation, which includes a thorough examination of modeling, analysis, and control at operating speeds below, equal to, and above synchronous speed. Stator equations are expounded through a reference framework run by the stator flux, while the rotor equations are in a synchronously rotating reference frame. Wind turbine miniatures are also made with indirect maximum power extraction control. Furthermore, the regulator of the GSC and RSC is set up so that the Network side converter Keeps up an unfaltering DC connect voltage and the RSC converter directs control. The d axis the rotor current maintains the reactive power demand of the DFIG, while q axis rotor current fulfill the reactive power demand. Similarly, the d-axis grid current maintains constant dc link voltage for wide variation of wind speed. The rotor-side and grid-side transducers are modeled separately to avoid erroneous results. The grid and rotor-side results from the rotor and stator circuits are shown to examine the energy exchange between the generator and the system during three (super synchronous, synchronous, and sub-synchronous) modes of operation.

碩士
國立中正大學
電機工程研究所
105
Over the last decade, the wind power penetration has increased substaintially because of the environmental consideration. With the integration of so much wind power generating capacity, the system operators are facing the challenges of maintaining the power system stability. Thus, the structure and accuracy of the wind turbine (WT) model are critical to the simulation and analysis of the large-scale power system. The use of the complex model to analyze the steady-state operation and dynamic stability of the power system requires long computation time and heavy computation burden. Accordingly, the generic models of the various WTs with the simplified structure and the adequate accuracy have been developed. This work develops both generic and complex WT models that are based on the doubly-fed induction generator (DFIG). The DFIG-based WT, which is the so-called type-3 WT, is the most popular in the world nowadays. To ensure that the developed generic and compex models can represent both electrical and mechanical characteristics of a real WT, the drive train and the pitch control with the anti-windup mechanism are included. Also, the mechanical transient due to the wind speed change is considered to make the both models more complete. This work compares the developed generic model with the developed complex model. Considering the complex model as the reference, several parameters of the generic model are adjusted. The simulation results demonstrate that the developed generic model of the type-3 WT reasonably approximates the developed complex model.

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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Although wind power as a renewable energy is assumed to be an all-round advantageous source of energy, its intermittent nature can cause difficulties, especially in the islanding mode of operation. Conventional synchronous generators can help to compensate for wind fluctuations, but the slow behavior of such systems may result in stability concerns. In this study, the virtual inertia method, which imitates the kinetic inertia of a synchronous generator, is used to improve the system’s dynamic behavior. Since the proposed method incorporates no long-term power regulation, it requires no mass storage device and is thus economical. To preclude additional costs, a rotating mass connected to the Doubly Fed Induction Generator (DFIG) shaft or a super-capacitor connected to the DC-link on a back-to-back converter of a wind power generator could be used. The concept and the proposed control methods are discussed in detail, and eigen-value analysis is used to study how the proposed method improves system stability. As well, the advantages and disadvantages of using DFIG rotating mass or a super-capacitor as the virtual inertia source are compared. The proposed approach also shows that while virtual inertia is not incorporated directly in long-term frequency and power regulation, it may indirectly enhance the system’s steady-state behavior. A time domain simulation is used to verify the results of the analytical studies.

This PhD thesis presents an innovative control strategy for the integration of renewable energy sources in distribution and transmission networks. This work is based on a multilevel control approach that takes into account the current technology, state of the art and legislative limits and considering the most promising trends. The outer loop control is based on a real time strategy for optimal power flow in presence of storage devices and wind turbine driven by Doubly Fed Induction Generators. These elements work in cooperation defining a dy- namic bus where the generated power is subject to temporal constraints, which establish a coupling between traditional power flow problems related to consecutive time periods; further the uncertainty in wind power genera- tion forecasts requires a continuous update of the planned power profiles, in order to guarantee a dynamic equilibrium among demand and supply. Model predictive control is used for this purpose, considering the dynamic equations of the storage and the wind turbine rotor as prediction models. A proper target function is introduced in order to find a trade-off between the need of minimizing generation costs and the excursions of the storage state of charge and the wind turbine angular speed from reference states. In the case study under consideration storage, wind turbines and a traditional synchronous generator are operated by the Transmission System Operator in the form of a Virtual Power Plant to cover network losses. The inner loop control is based on a real time control strategy for dy- namically balancing electric demand and supply at local level, in a scenario characterized by a HV/MV substation with the presence of renewable energy sources in the form of photovoltaic generators and an electric energy storage system. The substation is connected to the grid and is powered by an equiv- alent traditional power plant playing the role of the bulk power system. A model predictive control approach is proposed to decide in time the storage setpoint, based on the storage state of charge, the forecast demand and the forecast output of renewable plants. The two loops allow to obtain an overall control system able to minimize the generation of traditional power systems during the day-ahead market in an hand, and to respect the local load forecasts in other hand thanks the introduction of non-dispatchable renewable energy system and the energy storage ones as well as an innovative predictive control strategy. Theoretical results are reported on the stability of the proposed control scheme, which is then validated also on a simulation basis. Simulations show the effectiveness of the proposed approach in managing fluctuations of network demand and renewable generation under realistic conditions.
This PhD thesis presents an innovative control strategy for the integration of renewable energy sources in distribution and transmission networks. This work is based on a multilevel control approach that takes into account the current technology, state of the art and legislative limits and considering the most promising trends. The outer loop control is based on a real time strategy for optimal power flow in presence of storage devices and wind turbine driven by Doubly Fed Induction Generators. These elements work in cooperation defining a dy- namic bus where the generated power is subject to temporal constraints, which establish a coupling between traditional power flow problems related to consecutive time periods; further the uncertainty in wind power genera- tion forecasts requires a continuous update of the planned power profiles, in order to guarantee a dynamic equilibrium among demand and supply. Model predictive control is used for this purpose, considering the dynamic equations of the storage and the wind turbine rotor as prediction models. A proper target function is introduced in order to find a trade-off between the need of minimizing generation costs and the excursions of the storage state of charge and the wind turbine angular speed from reference states. In the case study under consideration storage, wind turbines and a traditional synchronous generator are operated by the Transmission System Operator in the form of a Virtual Power Plant to cover network losses. The inner loop control is based on a real time control strategy for dy- namically balancing electric demand and supply at local level, in a scenario characterized by a HV/MV substation with the presence of renewable energy sources in the form of photovoltaic generators and an electric energy storage system. The substation is connected to the grid and is powered by an equiv- alent traditional power plant playing the role of the bulk power system. A model predictive control approach is proposed to decide in time the storage setpoint, based on the storage state of charge, the forecast demand and the forecast output of renewable plants. The two loops allow to obtain an overall control system able to minimize the generation of traditional power systems during the day-ahead market in an hand, and to respect the local load forecasts in other hand thanks the introduction of non-dispatchable renewable energy system and the energy storage ones as well as an innovative predictive control strategy. Theoretical results are reported on the stability of the proposed control scheme, which is then validated also on a simulation basis. Simulations show the effectiveness of the proposed approach in managing fluctuations of network demand and renewable generation under realistic conditions.

Η παρούσα διπλωματική εργασία πραγματεύεται την ανάλυση της επαγωγικής γεννήτριας διπλής τροφοδοσίας (DFIG), την εξαγωγή μαθηματικών μοντέλων στο χώρο κατάστασης σε κανονική λειτουργία και σε λειτουργία με γραμμή μεταφοράς, την ενσωμάτωση PI ελέγχου της άεργου ισχύος στην πλευρά του δικτύου και τέλος την προσομοίωση του μοντέλου (με και χωρίς γραμμή μεταφοράς) σε περιβάλλον Matlab και την εξαγωγή συμπερασμάτων. Ειδικότερα Στο Κεφάλαιο 1 ξεκινάμε με μια επισκόπηση του ενεργειακού ζητήματος και την μέχρι τώρα χρήση της ενέργειας, παρουσιάζοντας τους λόγους που οδηγούμαστε προς τις Ανανεώσιμες Πηγές Ενέργειας (Α.Π.Ε) και κατ’ επέκταση στην εκμετάλλευση της αιολικής. Στο Κεφάλαιο 2 γίνεται μια γενική παρουσίαση των αιολικών συστημάτων. Περιγράφεται η εκτίμηση του αιολικού δυναμικού, η αεροδυναμική μετατροπή και ο έλεγχος της ενέργειας του ανέμου σε ηλεκτρική, καθώς και η τεχνολογία των ανεμογεννητριών, όπως διάφορα συστήματα και τύποι που βρίσκονται στην αγορά. Έπειτα στο Κεφάλαιο 3 ερχόμαστε σε επαφή με την DFIG, τα μέρη από τα οποία αποτελείται και τις δυναμικές εξισώσεις που την χαρακτηρίζουν, σύμφωνα με την θεωρία του διανυσματικού ελέγχου, σε ένα σύστημα κάθετων αξόνων. Με το Κεφάλαιο 4 περνάμε στην δυναμική περιγραφή της μηχανής στο χώρο κατάστασης έχοντας τοποθετήσει μεταξύ δικτύου και μηχανής μια γραμμή μεταφοράς, παρουσιάζοντας το πλήρες μαθηματικό μοντέλο που περιγράφει την λειτουργία της. Επίσης μελετώνται και τρόποι ελέγχου της DFIG. Στο Κεφάλαιο 5 γίνεται η προσομοίωση της μηχανής σε περιβάλλον Matlab, ενώ απεικονίζονται διαγράμματα που δείχνουν την συμπεριφορά της μηχανής σε διάφορες συνθήκες λειτουργίας της. Τέλος στο Κεφάλαιο 6 εξάγονται τα συμπεράσματα από τις προσομοιώσεις στην περίπτωση κανονικής λειτουργίας και λειτουργίας με γραμμή μεταφοράς.
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The book summarises the results of the DFG-funded coordinated priority programme \"Fast Algorithms for Material Specific Process Chain Design and Analysis in Metal Forming\". In the first part it includes articles which provide a general introduction and overview on the field of process modeling in metal forming. The second part collates the reports from all projects included in the priority programme.

The book summarises the results of the DFG-funded coordinated priority programme \"Fast Algorithms for Material Specific Process Chain Design and Analysis in Metal Forming\". In the first part it includes articles which provide a general introduction and overview on the field of process modeling in metal forming. The second part collates the reports from all projects included in the priority programme.