The idea of autonomous vehicles and automated highway systems is no new concept to the automotive industry. The potential benets of such a technology are numerous. The platooning approach would imply energy economy through air drag reduction, but also reduced trac congestion and increased safety. The question of longitudinal control in a platoon conguration is central, the main concern being relative to safety. In this thesis, dierent classical control approaches will be compared and applied to the platooning problem. Among these approaches, one was tested in November 2012 in a demonstration which involved three teams and multiple vehicles from dierent Swedish universities. Constrained optimal control comes with the prospect of increased safety and better handling of some characteristics of physical systems. The main negative impact of this constraint handling lies in its computational complexity. Numerical problems were encountered and described with the use of MPC. Proportional-Integral and Linear Quadratic controllers were retained and applied to the tracking problem in the context of vehicle platooning. These methods will be compared in a simulation environment.

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Providing reliable electricity to everyone is a very important matter nowadays. Both thetransmission system operator and the distribution system operator are acting on the grid inorder to insure it. The latter sometimes has to deal with problems regarding the voltage,especially in rural areas. Those issues are crucial because they might lead to a bad functioning ordamage some appliances, so they lower greatly the quality of supply. Moreover, the installationof new small producers such as wind power plants and solar panels to this network hasworsened the situation by complicating and multiplying the constraints. New methods are thusneeded to bring more flexibility to the distribution grid and consequently solve the voltageproblems and possibly others.The aim of this project was to test possible solutions to voltage problems in the lowvoltage network which is the part of the distribution grid directly connected to the finalconsumers. The main ones were the use of an on-load-tap-changer, capacitors and the controlof the producers connected at this level. At first, statistical models for the loads and theproducers were developed. The simulation itself was then designed and programmed. It isbased on Monte Carlo using a load flow procedure and takes into account a 30 years evolutionof the network. Finally, many cases were run to observe various behaviors and the mostinteresting ones were selected for the conclusions.The results showed that the on-load tap-changer is the possibility that adds the mostflexibility to the system and seems thus the best option due to the high randomness of theevolution of such networks. The other options tested are efficient in specific cases and cheaperso they might be interesting when it is possible to forecast the new customers and producers ofthe area, which is unfortunately not often the case. Finally, the negative effect of unbalance onsuch networks has been highlighted and it would be very good idea to develop procedures ableto give the best repartition of consumers among the phases at every bus in order to optimizeparameters such as voltage and losses.

The aim of this study is to define the minimum size of Statcom supporting the interconnection of a large offshore wind farm with high voltage direct current line commutated converters (HVDC LCC) and high voltage direct current voltage source converter (HVDC VSC) connected to a power system. The size of the Statcom is defined by using a simulation model consisting of a wind farm, HVDC LCC based transmission system, HVDC VSC based transmission system, a Statcom and the Cigr� Nordic 32 power system model. Each sub model in the simulation was validated individually. Different simulation cases were used to analyse the impact of Statcom in case of a fault. The different faults (one phase to ground, three phase to ground, line tripping and generator tripping) were applied to the power system for different connection points of the wind farm, i.e. the wind farm was connected to a strong and a weak connection point. The results showed that connecting the wind farm with transmission technology HVDC LCC to the strong point in the power system did not require any Statcom support because the system reached stability after the faults. When connecting the wind farm to the weak point there is a need of Statcom support for the transmission technology HVDC LCC otherwise the power system becomes unstable. Connecting the wind farm to a weak point by using the transmission technology HVDC VSC there was no need of Statcom. The graph below shows the Statcom size in the HYBRID HVDC (HVDC LCC and Statcom) depending on the rating of the offshore wind farm and the wind farm model.

This report deals with the impact of doubly fed induction generators on the stability of a power system. The impact was quantified by means of detailed numerical simulations. The report contains a full description of the simulation, and details of the small signal analysis performed to analyse the system. Before the simulation results are presented, a foundation is laid, explaining the theory required to understand the models used and the calculations performed in the simulation. The derivation of a model of a doubly fed induction generator is presented, along with a description of the model of a synchronous generator. These are used in the simulation and analysis of a multi-machine power system, consisting of both of these types of generators. An explanation of how dynamic simulations of power systems can be performed is also put forward. This is useful, not only for understanding the simulation performed for this report, but as a guide to performing simulations of this type. This is true also for a description of linearisation and small signal analysis contained in this report. The software package MATLAB is used to perform the simulations, and the small signal analysis. Since the method described in this report is very general, it can be used to perform similar power system simulations for other power systems, and with other software. Numerical simulations reveal that the addition of doubly fed generators, such as those in wind parks, to a power system improves the response of the system after small disturbances, but can worsen it after larger disturbances.

The purpose of the thesis was to further investigate the possibility to complement the rotary converters with a phase shifting device as a continuation of the work done in the master thesis; Load flow control and optimization of Banverkets 132 kV 16 2/3 Hz high voltage grid. With this modification, rotating converters can be used almost as flexible as static converters. The earlier thesis has come to the conclusion that the best way of compensating the phase displacement is with a series inductance. In this thesis the possibility to use capacitors instead of or in combination with inductors was investigated. To investigate this three different models were built: One for the railway between H�ggvik (Stockholm) and Boden; the same model that was used in the earlier thesis; it was used to confirm the results, one for the railway between Boden and Haparanda and one model that was the same as for the Haparanda track but half the distance. The models were built in the simulation program SIMPOW. The results from the simulations performed for the railway between Boden and H�ggvik confirmed the results from the earlier thesis, with a series inductance as phase shifter. For the railway between Boden and Haparanda one phase shifting device consisting of reactors and one consisting of a combination of reactors and capacitors were dimensioned. The railway with half the length compared to the Haparanda track was used to see if the length of the track in a low impedance transmission system has a large influence of the size of the reactances needed. From the simulation the conclusion can be drawn that the track length does not have a large influence when suitable reactances are chosen. It is the size of the load and the phase angle that matter when choosing reactances. For the Haparanda track it is possible to save power. With a phase shifter that consists of reactors that is placed in the converter station in Kalix, power savings of 340 MWh/year were achieved. With a combination of reactors and capacitors with the capacitors in the converter station in Boden and reactors in the converter station in Kalix power savings of 750 MWh/year were achieved.

Svenska Kraftnät is (together with the other transmission system operators of the Nordic power system) responsible for keeping balance between the generated and demanded power in the Nordic power system. Spontaneous load variations and system disturbances, however, lead to power imbalance followed by frequency variations. The frequency deviations can be limited to an acceptable level by the spinning reserve, mainly by hydro power control. But there are also other system properties which have a great influence on the frequency and system stability. The frequency and voltage dependence of the loads have a direct influence on the power balance. The load naturally decreases because of the frequency and voltage drop that occurs in case of a sudden drop of a generating unit. Moreover, the emergency power control of the HVDC-transmission is activated at lower frequencies. This Master thesis is based on studies performed with the simulation program PSS/E. The work results in a comprehensive investigation regarding the Nordic model of frequency control. The system design is of great importance in PSS/E. Therefore the turbines including their control systems and models for the frequency and voltage dependence of the loads are examined in detail. Further deeper analysis regarding the modelling of the spinning reserve in PSS/E is performed. New models are developed as an alternative to the existing model of the spinning reserve in PSS/E. Their effect on the power balance is examined to determine if the modification of the spinning reserve has any significant impact on the frequency control or stability of the system, that has to be considered before the new model is implemented in PSS/E.

The voltage regulation in Fortum Distributions medium voltage network in Stockholm does not work satisfactory. This results in too high distribution voltages with many customer complaints as a consequence. The reason is the model responsible for compensating for voltage drops in the distribution network. Despite several adjustments Fortum has not been able to find the source of the high voltages and has therefore appointed an investigation in the form of a thesis work. The aim of this investigation is to locate the error and to produce a proposal regarding the solution of this error using the existing system, common industrial knowledge, state of the art research and the option to use voltage readings from the different substations. The conclusion of this master thesis is that the largest contribution to the high voltage levels is made by the large compensation for distribution loses. Furthermore an additional error in the model has been found. Therefore this master thesis recommends Fortum to abandon the existing system and instead utilize the option to use voltage readings from the different substation.

A detailed methodology and consistent results related to the evaluation and validation of the Multiple Infeed Short Circuit Ratio as an index of the system strength in a particular point for Double Infeed HVDC systems are presented in this thesis. The evaluation will be carried out by comparing the critical MESCR with respect to the critical Short Circuit Ratio for a Single Infeed HVDC system. These critical values represent the weakest AC-network that connected to the inverter is able to keep the system stability after a disturbance. These stability limits are obtained by studying the risk of voltage instability. The results presented in this work conclude that the validation is positive and the stability limit can be set in 1.3.

Because of increasing demand of power on Malmbanan the capacity of the existing wires which supply the trains must be increased. This increases the stress on the existing poles and for this reason the system for supplying the loads along the railway is to be removed from the poles and be replaced by some other system. This thesis is a study on a two-level low voltage (1 kV and 0.4 kV) electrical system with the aim to investigate if it can be an alternative to the system used today taking into account the voltages, fault currents and costs. In this thesis the following tasks have been performed: � Gathering of data � Description of basic theory � Loadow and fault current calculations of the system with MATLAB � Life Cycle Cost estimate of the system � Analysis and conclusions from the results The results show that the new system can be an alternative to replace today's system. The simulations and calculations show that the voltage drop is at an acceptable level and that the fault currents are large enough to supply a safe disconnection if a fault occurs at the far end of the system.