Les travaux de recherche présentésdans cette thèse ont été effectués dans le cadred'une collaboration entre Leroy Somer et lelaboratoire de génie électrique et électronique deParis (GeePs). Ils ont pour objectif lessimulations des phénomènes observés en modetransitoire des machines électriques. Cessimulations sont particulièrement orientées parles nouvelles exigences issues du Grid Code pourles alternateurs connectés au réseau.Principalement, deux types de modèles ont étédéveloppés. Le premier se base sur unereprésentation de l’état magnétique de lamachine où chaque flux est exprimé en fonctiondes courants des différentes bobines. Le secondmodèle regroupe les courants en utilisant descourants magnétisants sur les axes d et q associésà des coefficients de saturation pour chaque fluxet simplifie la représentation magnétique,notamment pour la prise encompte du circuit amortisseur. Avec unemodélisation suffisamment précise ducomportement magnétique non linéaire de lamachine, ils permettent de mieux prédire lescourants et le couple électromagnétique lors desdéfauts tels que les creux de tension. Les travauxeffectués présentés dans ce mémoire ont permis,en partant des descriptions des saturationstrouvées dans une machine, de définir desméthodes pour incorporer la saturation dans lesmodèles de type circuit et finalement d’aboutirau choix du modèle non-linéaire pour unemachine électrique donnée. Grâce à un temps decalcul réduit, ils ont aussi conduit à l'intégrationsous Simulink de modèles de la machine et dusystème d'entrainement pour la réalisationd'études de stabilité et pour créer unenvironnement de mise au point de la commandedu système. / The research presented in this thesiswas carried out in the research and developmentproject between Leroy Somer and the Group ofElectrical Engineering of Paris (GeePs). Theirobjective is to simulate the phenomena observedin the transient states of electrical machines.These simulations are particularly oriented bythe new Grid Code requirements for alternatorsconnected to the power network. Two types ofmodels have been principally developed. Thefirst one is based on a magnetic description ofthe machine where each flux is expressed as afunction of the currents flowing through thedifferent machine windings. The second oneregroups the different winding currents by usingthe magnetizing currents on axes d and qassociated to saturation coefficients for eachflux linkage and simplifies the magneticdescription, especially when taking into accountthe damper windings. With a sufficiently precisemodelling of the non-linear magnetic behaviourof the machine, it is possible to better predict thecurrents and the electromagnetic torque underfault conditions such as voltage drops. The workcarried out in this thesis has made possible,starting from the descriptions of the saturationeffects found in a machine, to define methodsfor incorporating saturation into circuit models.Finally, one can make a choice of the dynamicnon-linear model for a given machine. Thanks toshort computation time, it also led to theSimulink integration of the machine andexcitation system models paving the way forstability and control studies.

Grid codes are becoming more demanding on power generating units due to the factthat the complexity of the power grid is increasing. The penetration of wind powerhas grown over the last years and it is clear that wind farms need to be addressedwith the same type of grid codes as conventional generation units. There is howeveran undeniable difference between the technology in conventional synchronousgeneration units, and the asynchronous generation units in wind farms. This thesis has reviewed the current grid code in Sweden and compared it to the newcode proposed by ENTSO-E, “the Requirements for Generators”, in the aspect ofwind farms with an installed power of 30 MW or more. The comparison has beencomplemented by an analysis of how wind farms of two different technologies(Doubly fed induction generators and full power converters) can meet therequirements and technical proposals have been given on how to be able to meetcompliance with the new grid codes. The Requirements for Generators contains many non-exhaustive and optionalrequirements, because of this it has been difficult to, at this stage, exactly point outthe technical impact on the grid connection of future wind farms in Sweden. For manyof the requirements in the Requirements for Generators there is no equivalent in theSwedish Grid Code (SvK FS2005:2) but counterparts can thus be found in existingpractices and therefor does not imply any major differences for the industry. The requirements of frequency regulation, synthetic inertia and reactive powercapability are the main components of the RfG which will require additional softwareand hardware installations for future wind farms in Sweden.

This thesis first develops a medium-voltage grid code outlining stringent requirements for low-voltage ride-through, high-voltage ride-through and ancillary services based on anticipated grid requirements for distributed energy resources (DER)s. A 100 kW generating capacity DER study system is then formulated taking into consideration key design constraints as motivated by the medium-voltage grid code. Local DER system controls are developed that enable existing systems employing conventional current-control for the grid-interfacing voltage-sourced-converters to comply with the grid code. A supervisory controller is proposed that allows multiple DER units and loads to operate collectively as a DER system with a single point of common coupling. The impact of transformer configurations, fault types and fault locations on DER systems are quantified through a comprehensive fault study using the PSCAD/EMTDC software package. A subset of these fault scenarios are identified for rapid screening of DER system compliance against low-voltage ride-through requirements.

This thesis first develops a medium-voltage grid code outlining stringent requirements for low-voltage ride-through, high-voltage ride-through and ancillary services based on anticipated grid requirements for distributed energy resources (DER)s. A 100 kW generating capacity DER study system is then formulated taking into consideration key design constraints as motivated by the medium-voltage grid code. Local DER system controls are developed that enable existing systems employing conventional current-control for the grid-interfacing voltage-sourced-converters to comply with the grid code. A supervisory controller is proposed that allows multiple DER units and loads to operate collectively as a DER system with a single point of common coupling. The impact of transformer configurations, fault types and fault locations on DER systems are quantified through a comprehensive fault study using the PSCAD/EMTDC software package. A subset of these fault scenarios are identified for rapid screening of DER system compliance against low-voltage ride-through requirements.

Nordex, a wind-turbine manufacturer and developer, has just launched the development activity over Belgium’s French-speaking Region – the Walloon Region – with the current political context favorable to wind energy deployment. Since the Walloon market is unknown, the master thesis aims to identify the appropriate approach to use for optimal wind farm development and the critical issues that may impinge on it. The scope of the master thesis is thus to find two to three sites well suited for wind farm implementation in the province of Luxembourg and to develop these sites.  An exhaustive study of the wind farm potential of the province of Luxembourg has been led, based on geographic data analysis with the GIS ArcGIS®, feasibility studies conducting, meetings with districts’ administration as well as visits onsite. In addition, a thorough comparative analysis of the Belgian specification for grid connection has been performed to identify any requirement that is not included in the French and German grid codes, which are the benchmarks of the development activity in Nordex France. Many obstacles have been encountered in wind farm development, chiefly a strong existing competition in the wind energy sector and a limited grid capacity. In addition time can be a friend but it can also sometimes be a foe at some stages that rely on public administration. Consequently from the 40 identified sites with ArcGIS®, only three have succeeded. Regarding the Belgian requirements for grid connection, all can be met thanks to an existing German specification data sheet. Eventually the Walloon policy towards wind energy development is expected to evolve so as to foster wind farm deployment in Wallonia and to reach the objectives set for 2020 (2200 MW of installed wind capacity while in January 2011 only 440 MW were in operation). Consequently to that, Nordex’ approach may have to adapt to the new regulations.

Technological improvements on wind energy systems with governmental supports have increased the penetration level of wind power into the grid in recent years. The high level of penetration forces the wind turbines stay connected to the grid during the disturbances in order to enhance system stability. Moreover, power system operators must revise their grid codes in parallel with these developments. This work is devoted to the modeling of variable speed wind turbines and the investigation of fault ride trough capability of the wind turbines for grid integration studies. In the thesis, detailed models of different variable speed wind turbines will be presented. Requirements of grid codes for wind power integration will also be discussed regarding active power control, reactive power control and fault ride through (FRT) capability. Investigation of the wind turbine FRT capability is the main focus of this thesis. Methods to overcome this problem for different types of wind turbines will be also explained in detail. Models of grid-connected wind turbines with doubly-fed induction generator and permanent magnet synchronous generator are implemented in the dedicated power system analysis tool PSCAD/EMTDC. With these models and computer simulations, FRT capabilities ofvariable speed wind turbines have been studied and benchmarked and the influences on the grid during the faults are discussed.

The continuously increasing energy penetration from wind farms into the grid raises concerns regarding power quality and the stable operation of the power system. The Grid Code´s requirements give strict guidelines for a wind farm´s behaviour under faulty or abnormal operating conditions.The primary purpose of this project is the application of a STATCOM for wind farm integration complying with the Grid Code. Towards that, an outer control strategy for the converter is designed so as to regulate the voltage at the point of common coupling by providing reactive power compensation. Thus the safe operation of the grid will be ensured since the wind farm will follow the Grid Code´s standards.The existing Grid Code requires only a positive sequence current controller. This study attempts to investigate whether this is sufficient or not and to examine the possibility of extending the Grid Code requirements so as to incorporate a negative sequence current controller as well. The results support the latter suggestion. Also, the use of SiC devices was also considered in this project. / Den ständigt ökande penetrationen av vindenergi i elnätet väcker farhågor om elkvalitet och stabil drift av kraftsystemet. Nätkoden (Grid Code) ger strikta riktlinjer för en vindkraftsparks beteende i felfall och under onormala driftsförhållanden.Huvudsyftet med detta projekt är att använda en STATCOM för integration av vindkraftsparker så att nätkoden uppfylls. I detta projekt utformas en yttre reglerstrategi för omriktaren för att reglera spänningen vid anslutningspunkten för vindkraftsparken genom att tillhandahålla reaktiv effektkompensering. Därigenom uppnås en säker drift av nätet eftersom vindkraftparken kommer att följa nätkoden.Den befintliga nätkoden kräver endast styrning av plusföljdskomponenten av strömmen. Denna studie försöker undersöka om detta är tillräckligt samt undersöka möjligheten för att utvidga nätkoden genom att införa ett krav på styrning av negativ-sekvens ström. Resultaten stöder det sistnämnda förslaget. Även användningen av halvledarkomponenter av kiselkarbid-SiC studerades i detta projekt.

Year 2040 the goal is to have a 100 % renewable Swedish energy system. Svenska kraftnät (Svk) predicts fully decommissioned nuclear power plants and an increased amount of connected wind power plants, especially offshore, year 2045. These kind of renewable power plants are non-synchronous and do not provide the grid with the same system stability services naturally as synchronous generators, such as nuclear power plants. With the increased number of renewables connected, one future challenge is to maintain the stability of the power grid. Grid stability can be divided into voltage-, frequency- and rotor angle stability.This thesis has investigated how large-scale offshore wind power plants (OWPPs) can contribute with reactive power compensation and in turn voltage stability to a nearby onshore power grid in Sweden. The evaluation has been done from the perspective of the TSO and the OWPP owner interests, with a focus on grid codes, economic incentives and technical capabilities.This project has been made in three parts. First, a comparison of voltage stability control requirements in different European grid codes was made. Secondly, static power flow simulations of a case study of a 1000 MW OWPP have been performed in PowerWorld Simulator, testing the OWPP’s reactive power outputs under different circumstances. Thirdly, a market opportunity analysis has been completed, analyzing reactive power market opportunities for OWPPs as well as for TSOs.The study shows that the reactive power capabilities of the simulated OWPP is considerable higher than the Swedish grid codes requires. Thus, an opportunity is to make the grid codes stricter, in combination with economic incentives. The case study showed that the distance offshore has an impact of the reactive power reaching the grid onshore. Though, the OWPP’s contribution to local voltage stability onshore is considered as good. Finally, with short- and long-term contracts, a reactive power market can be favorable for both the OWPP owner and the TSO.

The integration of dispatchable renewable energies like biomass, geothermal and reservoir hydro technologies into an electrical network present no greater challenge than the integration of conventional power technologies for which are well understood by Eskom engineers. However, renewable energies that are based on resources that fluctuate throughout the day and from season to season, like wind and solar, introduce a number of challenges that Eskom engineers have not dealt with before. It is current practice for Eskom‟s generation to follow the load in order to balance the demand and supply. Through Eskom‟s load dispatching desk at National Control, generator outputs are adjusted on an hourly basis with balancing reserves making up only a small fraction of the total generation. Through the Integrated Resource Plan for Electricity of 2010, the Department of Energy has set some targets towards integrating renewable energy, including wind and solar generation, into the South African electricity market consequently introducing variability on the supply side. With demand that varies continually, maintaining a steady balance between supply and demand is already a challenging task. When the supply also becomes variable and less certain with the introduction of non-dispatchable renewable energy, the task becomes even more challenging. The aim of this research study is to determine whether the resources that previously helped to balance the variability in demand will still be adequate to balance variability in both demand and supply. The study will only concentrate on variable or non-dispatchable renewable energies as will be added to the South African electrical network according to the first two rounds of the Department of Energy‟s Renewable Energy Independent Power Producer Procurement Programme. This research study only looks into the balancing challenge and does not go into an analysis of voltage stability or network adequacy, both of which warrant in depth analysis. / Thesis (MIng (Development and Management Engineering))--North-West University, Potchefstroom Campus, 2013.

The integration of dispatchable renewable energies like biomass, geothermal and reservoir hydro technologies into an electrical network present no greater challenge than the integration of conventional power technologies for which are well understood by Eskom engineers. However, renewable energies that are based on resources that fluctuate throughout the day and from season to season, like wind and solar, introduce a number of challenges that Eskom engineers have not dealt with before. It is current practice for Eskom‟s generation to follow the load in order to balance the demand and supply. Through Eskom‟s load dispatching desk at National Control, generator outputs are adjusted on an hourly basis with balancing reserves making up only a small fraction of the total generation. Through the Integrated Resource Plan for Electricity of 2010, the Department of Energy has set some targets towards integrating renewable energy, including wind and solar generation, into the South African electricity market consequently introducing variability on the supply side. With demand that varies continually, maintaining a steady balance between supply and demand is already a challenging task. When the supply also becomes variable and less certain with the introduction of non-dispatchable renewable energy, the task becomes even more challenging. The aim of this research study is to determine whether the resources that previously helped to balance the variability in demand will still be adequate to balance variability in both demand and supply. The study will only concentrate on variable or non-dispatchable renewable energies as will be added to the South African electrical network according to the first two rounds of the Department of Energy‟s Renewable Energy Independent Power Producer Procurement Programme. This research study only looks into the balancing challenge and does not go into an analysis of voltage stability or network adequacy, both of which warrant in depth analysis. / Thesis (MIng (Development and Management Engineering))--North-West University, Potchefstroom Campus, 2013.