In this report, the static and dynamic impact on the transmission grid in the south of Sweden has been studied when connecting two large wind farms. The two wind farms are Lillgrund, 150 MW, and Krieger’s Flak, 640 MW. The study has been performed using the software Power System Simulator for Engineers, PSS/E. The static study shows no problem with voltage level or losses. However, during low load situations, the 135 kV lines between Trelleborg and Sege risk becoming overloaded. This problem must be addressed before both wind farms are allowed to be connected to the system.Dynamically, the implementation of a dynamic model for Baltic Cable is vital for the study. The cable has dynamic effects, like commutation failure in the converter station in Kruseberg, that need to be modelled. The simulations show a need to install an SVC if wind turbines equipped with ordinary fixed speed induction generators are used. Simulations with General Electric’s dynamic model for its 3.6 MW wind turbine show that there is no need to install an SVC in order for the voltage to re-establish. However, no comparison with actual data has been made so the correctness of the model can not be checked. The simulations also show a low impact on the system when disconnecting both wind farms simultaneously. Finally, no problems with rotor angle stability have been found.

The power system modelled in this thesis work has been developed for simulationwhen e.g. the production in some part of the power system is changed. The powersystem has been modelled according to the swing mass of the system, the frequencydependency of the load and the turbine governor. The model determines the systemfrequency, the period of regulation and the power exchange between the differentsubsystems in the Nordic synchronized system.In this model the system frequency is assumed to be the same in all different parts ofthe power system and the voltage conditions in the power system are neglected. Forthat reason power swings does not occur between different subsystems in the powersystem, which usually occur as a result of the swinging connection between thetransmissions line. The loads in this power system are modelled to be voltageindependent.The power system has been implemented in Matlab Simulink. The model has beenimplemented according to different transfer block functions, such as transferfunctions, amplifiers and limiters. Two different power systems have been developedin this model, a 3-district model and a 10-district model. The 10-districts model is thesubdivision of the Nordic synchronized system in 10 districts. The number of districtsdefines the number of hydropower or steam power block functions with swing massesin the model, i.e. there are three hydropower block functions with swing masses in the3-district model. In both power systems the loads are modelled to be frequencydependent and controlled according to the turbine governor in the system. Thehydropower block functions in the power system can easily be changed to i.e.windpower block functions.The power system modelled in this thesis work was compared to a more accuratesimulation, (real time simulation) which is for ARISTO-simulation. Comparisonbetween the result of this model and simulations in the real time simulator are made tostudy i.g. the change of frequency when the system production is increased.Two different user interfaces have been implemented in this thesis work. The firstuser interface has been implemented to carry out the change of the control parametersand system parameters during the simulations. The second user interface has beenimplemented to analyze the result of the simulation at the end of the simulation. Forthe whole system or only for a part of the power system the user can analyze thefrequency of the system, the turbine power, the generated power from the machines,the power at the loads and the power imbalance.5

The voltage level in the power grid varies due to variations in load and production. Normally these variations are manageable, but they may be excessively large during a disturbance. If the voltage is too high it may damage the equipment in the grid and too low voltages may cause problems like voltage instability. The magnitude of the voltage variation depends on the short circuit power capacity of the point of interest.This problem may become lore prominent due to automatic voltage regulation that acts on shunt reactors and shunt capacitors. When the shunt reactor is connected or disconnected to the grid it may cause such large changes in the voltage that the shunt reactor starts hunting. Hunting is a phenomenon that manifests itself in a sequence of undesired connection and disconnection of some reactive compensation equipment connected in shunt. Hunting may also include shunt capacitors, and the emergency power and special protection schemes that acts on the HVDC links may increase the hunting problem.An earlier master thesis done at Svenska Kraftnät analysed the hunting problem in the middle parts of Sweden. Svenska Kraftnät now finds it suitable to analyse the problem with hunting for the southern part of Sweden.The main task in this master thesis is to present new settings for the automatic voltage control in the southern parts of Sweden, 400-130 kV. The purpose of this is to minimize the risk encountering of hunting. The thesis should also include an inquiry of reversed voltage control. The purpose of this is to raise the voltage limit that controls the activation of shunt capacitors in Sydkraft’s 130 kV grid and evaluate the impact of this action on the hunting problem.The work will be performed with the real time simulator ARISTO.One of the major findings of this thesis work can be summarized as follows.Due to a fairly wide range of operation conditions, finding a single set of optimal settings for the voltage automatics appears to be infeasible, at lest in general. But there are settings that can reduce the risk with hunting e.g. to separate the time settings in buses close to each other.

The short-term (1 to 48 hours) predictability of wind power production from wind power plants in a power system is critical to the value of wind power. Advanced wind power prediction tools, based on numerical weather prediction models and designed for power system operators, are being developed and continuously improved. One objective of the EU-supported WILMAR (Wind power Integration in Liberalised electricity MARkets) project is to simulate the stochastic optimization of the operation of the Nordic and German power systems, in order to estimate the value of potential improvements of wind power prediction tools. For power system simulations including wind power, a model must be developed to simulate realistic wind speed predictions with adjustable accuracy, in which the correlations between wind speed prediction error at the spatially distributed wind power plants is accurate. The simulated wind speed predictions are then converted to aggregate wind power predictions for regions within the Nordic and German power systems. A Wind Speed Forecast Error Simulation Model, based on a multi-variate ARMA(1,1) time-series model, has been developed in Matlab. The accuracy of the model in representing real wind speed predictions in Denmark has been assessed, and various errors resulting from practical limitations of input data have been quantified.

Modern society is largely dependent on electricity supply and Transmission System Operators (TSOs)have to ensure the reliability of supply in situations that are increasingly difficult to manage due tohigher consumption levels and variability of new intermittent energy sources. In order to ensure thesystem’s safety, voltage stability is a matter of prime importance and is dealt with for different timeframes.Ahead, new reactive power compensation means are installed to prevent voltage collapse. Then, if avoltage collapse gets under way, ultimate mitigation measures have to be taken: Load Tap Changershave to be blocked because of their negative action in critical situations.The first objective of this Master’s Thesis consists on the development of a method to optimize theLTC blocking parameters through dynamic simulation. Then, this method has been applied in fourregions of the French grid and the results have been implemented in the end of the year 2012.The second objective of this Master’s Thesis consists of the development of a method to assess theeconomic gain thanks to the investment in reactive power compensation means for the French TSO.

Some applications such as industrial automation, cargo handling, warehouse managing,monitoring of autonomous robot or personnel localization, require reliable indoor positioning. In particular, the requirement is to accurately localize a mobile wireless node in real-time. In outdoor scenarios, Global Navigation Satellite Systems (GNSSs) are commonly used for positioning. Nevertheless, they present notable shortcomings for being used in indoor applications. The principal disadvantages are the low accuracy achieved and the attenuation and reflections introduced by buildings and other structures, which make impossible their use in most cases. The fixed and smaller operational area of an indoor positioning application in comparison with the area of an outdoor application makes it possible to install a radio positioning infrastructure. Concretely, the Ultra Wide Band (UWB) positioning system considered in this thesis consists of nodes installed in fixed and known positions (slaves) and a mobile node of unknown position (master) which is the one to be localized. The operation of the system is based on calculating the distance from the master to the slaves by measuring the Round-Trip-Time of a UWB pulse. In this way an estimate of the position can be obtained, with the advantage of having bounded errors,but, in contrast, the estimations have a low dynamic range and other navigation information cannot be measured. The master has some sensors attached, an Inertial Measurement Unit (IMU) and a Dead-Reckoning (DR) system. By propagating the navigation equations, estimates of the position and other navigational states can be obtained, but with the disadvantage of having errors that grow with time. The solution of the problems related to the individual location systems is using information fusion algorithms. Such algorithms, by means of integrating different sources of data, in this case the UWB range measurements and the IMU and DR measurements, create a positioning system which combines the benefits of the individual systems. In this project the aim is to develop, implement and evaluate sensor fusion algorithms. In particular, the developed algorithms are based on the Extended Kalman Filter and the Particle Filter. Furthermore, they have been adapted to different dynamic models, in order to find the algorithms which fit better with the motion of a mobile node. The developed algorithms have been tested with simulated trajectories using Matlab, and with real experimental datasets acquired by a mobile robot. The results show the benefits of the information fusion, since the accuracies obtained in the estimations outperform the accuracies obtained with the individual systems. Also in the most unfavorable cases, when one of the sources has high errors in the measurements, the algorithms are able to discard the useless information and estimate using only the useful measurements, proving the robustness of the system.

Interconnection between France and Italy under the Alps could impact the European power system stability. Indeed, the HVDC lines are active elements of electrical grid that influence its dynamic behaviour in case of disturbances. Extensive studies must be run to precisely determine the specifications of this cross-border link and its conversion stations. These studies require models as precise as possible of the European network. The best available model at present for the synchronous network of continental Europe is the Dynamic Reference Model (DRM), which was compiled in the framework of the IPS/UPS study [6]. It modelled a winter situation (high peak load) and the first task of the Master Thesis consisted in the development of a summer situation (low load period) of this model. In this way, it would be possible to perform stability studies in both situations to obtain more precise and reliable results. The DRM models for winter summer situation were firstly designed to study small-signal stability and especially inter-area mode, i.e. electromechanical oscillations between two groups of machines. In the perspective of transient stability studies in the area of the future HVDC line between France and Italy, this model had to be updated. Detailed versions of regulators and transformers were therefore implemented in order to model more precisely the transient dynamic behaviour of French machines. An update of the dynamic data of the Italian power system had also to be performed with new detailed versions of regulators created. Furthermore, the European synchronous electric power system is becoming larger with interconnections of new countries, such as Turkey in 2011 and other ones in the future. Because of this on-going enlargement, new phenomena concerning inter-area modes might occur. In this new context, benchmarks had been created to develop and test a new methodology for tuning the regulators’ parameters of synchronous generators.

The role of quality control is to correctly translate customers´ requirements into materialized products to achieve customers’ satisfaction. Today Product Development Process (PDP) becomes the stage to improve and to obtain successful products. In the 1980s, Six Sigma appeared as an attempt to improve some aspects of products and services in order to reduce failures in production as much as possible. But there still was a lack of customer perspective over product development project. This thesis approached the lack of customer insight with a new product development process, Design for Six Sigma (DFSS). Examples that describe how DFSS works and its implementation are still missing, therefore the purpose of this master thesis is to prove if the implementation of DFSS would be efficient, effective and closer connected to the customer of mass- production companies. DFSS is based on processes, roles and tools. However, it is questionable whether the suggested role structure and a uniformed process are able to implement in the real world. The methods used for this research project were two interviews with two mass customization companies, qualitative data collection and finally analyzing the collected data by comparing them with the theory of DFSS. This PDP ensures the track, and enhances creativity and innovation, taking the process beyond its capabilities. Moreover, the conclusions of the thesis show that there is no need for a uniformed model, making DFSS more useful and trickier for competitors. The lack of a uniformed model allows to overcome the innovative ability. The skills to reach these roles and the creation of a team within the company are more important than roles and backgrounds themselves. In spite of knowledge of expertise areas, the task is more related to control the collaboration, communication and flow of information within the group. DFSS becomes a successful solution for customer insight, a good combination of tools and techniques. But it does not mean that implementing accurately a certain methodology is the right solution.

In today’s high power VSCs (Voltage Source Converters), IGBTs (Insulated Gate Bipolar Transistors) are the dominant semiconductors. These converters are in general modular multilevel based and contain several building blocks that are series connected. Each of these building blocks in turn consist of several series connected IGBT valves. One of the advantages of using modular multilevel based VSCs is the ability to switch each building block at a lower frequency compared to the average total switching frequency of the converter. IGBTs generally have lower switching losses than other semiconductors, however, their on-state losses are higher because of a larger on-state voltage. Furthermore, series connection of IGBTs devices imposes voltage sharing complications that are generally difficult to deal with. A solution to this problem is to increase the amount of series connected building blocks and thus avoid series connection of semiconductors. To lower the semiconductor on-state losses, either the IGBTs are replaced by improved IGBT and drives or an alternative semiconductor that is more suited for modular multilevel topologies can be used. In this thesis, an alternative semiconductor called IGCT (Integrated Gate-Commutated Thyristor) is studied; more specifically RC-IGCT (Reverse Conducting IGCT). An analytic analysis is conducted to grasp the switching behavior, furthermore, a simulation model in PspiceR is proposed for confirming the analytic analysis. This model is also used for parameter sweeps of clamp circuit components from which a table is created. This table can be used for comprehending the effects of changing values on the switching transient and also for the design of clamp circuit components. However, a numerical and a graphical method together with the PspiceR model are proposed for designing the clamp circuit. It is found that the graphical method is far more intuitive and revealing than the numerical. If further accuracy is required, then the graphical method can be used in tandem with the numerical. A fault case analysis of the clamp circuit is conducted in order to reveal how failures in the clamp components affect the semiconductors and other components in a building block. Some of these failures are more destructive than others. The IGCT building block states and current paths are discussed and finally series connection of IGCTs is considered.

Several research activities at KTH are carried out related to Isolated AC/DC converters in order to improve the design and efficiency. Concerning the improvement in the mentioned constraints, losses of the elements in the prototype converter are modeled in this thesis work. The obtained loss model is capable of calculating the losses under different circumstances. The individual contribution of losses for each element at different conditions can be obtained, which is further useful in improving the design and therefore, efficiency. The losses in different elements of the converter, including power semiconductor devices, RC-snubbers, transformer and filter inductor at different operating points can be computed by using the obtained model. The loss model is then validated by comparing the analytical results with the measurements. The results based on developed loss model show consistency with the measured losses. The comparison at different conditions shows that, the difference between measured and analytical results ranges between 10% to 20 %. The difference is due to those losses which are disregarded because of their negligible contribution. On the other hand, it is also observed that if the neglected losses are counted, the difference reduces up to 10%.