There is an increasing amount of power processed through power electronics in the areas of generation interface, energy storage and loads. This increment enables possibilities for improved solutions for efficient generation and use of electric power. Traditionally loads in AC distribution systems have been seen as passive and individual elements rather than active components of the system. An AC distribution system with high percentage of power electronic loads can be susceptible for instability under abnormal operation conditions if the converter controls are not designed for such conditions. This thesis introduces a solution of reactive current control for a constant power load (CPL) in an AC distribution system. A CPL is a load that draws a constant amount of active power without regard to any drops in system voltage. The resistance seen from the AC distribution system to the CPL is known as a negative input resistance which is characteristic for this kind of load. A drop in AC system voltage will result in increased current and vice versa. Hence the resulting resistance will be negative. Negative resistance behaviour is not favourable for system stability and the work has focused on a control of the converter that reduces the instability effect of the load. By controlling the reactive current component to inject current for support of the AC distribution system voltage during faults and other interferences, the load becomes an active participant in the AC distribution system. An AC distribution system has been built in PSCAD/EMTDC. An asynchronous generator and a fixed capacitor are used as distributed generation. The CPL consists of an AC/DC converter and a voltage dependent current source in order to keep constant DC power at the load. Focus has been on the converter control implementing a voltage oriented vector control based on a two phase rotational reference frame. Measurements of current and voltage with different voltage drop levels have been done for comparison of a CPL with and without reactive current control. The simulation example has verified the negative resistance phenomenon of the CPL. Results shows that the AC system voltage is less vulnerable in case of faults if the converter control is designed to inject reactive current into the AC distribution system.

Offshore wind power has proven to be a renewable energy source with a high potential, especially in the North Sea, where an important development is going on. The location of the wind farms tends to move far from the coast to benefit stronger and more constant wind. In the same time, the power output of the wind farm is increasing to several hundreds of MW up to 1 GW. In the European liberalized electricity market, the interconnection of the countries become very important to facilitate the cross-border trade of electricity but also to improve the reliability of the grid. Combining this both aspects into one, a big offshore HVDC grid connecting countries and large wind farms spread allover the North Sea is currently being studied and developed. So in addition of the challenge given by a high penetration of the wind power production in the European power production scheme, new challenges are opened especially for the offshore transmission. This master thesis presents the integration to grid of a single 1 GW or a cluster of wind farms connected to an oil rig with different connection scheme based on HVDC transmission using the Voltage Source Converter (VSC) technology. The connection of the offshore wind farms is done either with a single HVDC transmission or two HVDC transmissions connected to the main grid at two different Points of Common Connection situated in the south-west of Norway. The wind farms are not represented in detail but by a single generator. They are equipped for the simulation with Double Fed Induction Generators (DFIG) to be representative of the reality, almost half of the wind turbines are today equipped with DFIG technology. Two disturbances are used to test the electrical stability of the system: a classical 150ms three fault phase in agreement with the grid code requirements on the ride fault through requirements and 100ms fault leading to the tripping of a line. The impact of using different types of generator is also investigated with the simulation of cluster wind farm where a wind farm is equipped with Fixed Speed Generator (FIG). The emphasis is put on the response of the VSC-converter and to a lesser extent on the behaviour of the wind turbine generator. It is demonstrated the capacity of the VSC-converter to stabilize a small grid alone and to “isolate” a disturbance. The voltage and the frequency offshore are practically unaffected by a fault onshore and vice versa. As expected, it is demonstrated that the multiplication of the VSC-HVDC converter in a grid improves the stability of the system. Finally, it has been noticed that there maybe some interactions if several different types of generators are used. The replacement of a generator by another type inside the wind farm cluster may change completely the dynamic behaviour after a disturbance. Simulations are performed with PSS/E.

Problem description: The objective of this project was to create a simple model of the European power system and to investigate the effect an increasing amount of on- and offshore wind power will have on the North European power market in general and Norway in particular. The scenarios contain increasing amounts of installed wind power capacity, both on- and offshore. Emphasis was to be on the area surrounding the North Sea. The project covers the following issues: - Simulations of simplified power system scenarios set in the years 2005, 2020 and 2030. - Study how an increasing amount of installed wind power will affect energy prices, power production distribution, and power transmission flows. - Investigate how an offshore grid consisting of interconnections between offshore wind farms will affect the system. The task: The simulations in this project were performed using simple power market model. The model included 6 price areas: Denmark West, Denmark East, Norway, Sweden/Finland, Germany and UCTE/Others. The existing market model was modified in the following manner: - Split Norway into three price areas: Norway North, Middle and South - Add the Netherlands - Add the United Kingdom - Add corresponding offshore price areas for areas neighbouring the North Sea. Wind series were generated for each wind generator using reanalysis data. Scenarios were created for the years 2005, 2020 and 2030. In these scenarios, wind power capacities are increasing as time progresses. The 2020 and 2030 scenarios have been simulated with two alternative grid configurations: one where the offshore areas are connected only to their respective onshore areas and one where the offshore areas are also interconnected in an offshore grid. In total 7 different scenarios were simulated. Results: Wind power is able to supplant a large share of energy originally produced by con-ventional thermal generators. The presence of an offshore grid does not have any dramatic effects on energy production for the system, though it is possible to conclude that the presence of an offshore grid may contribute to slightly shift the power system in favour of renewable energy sources. Wind power will cause a significant reduction in energy prices in all areas, resulting in reduced energy costs for the entire system. Analysis of lost wind and hydro power reveals the importance of sufficient transmission capacity when large quantities of wind power are added to the system. Scenario 4 features enormous quantities of lost hydro power in the North and Middle of Norway due to transmission limitations. Analyses of power transmissions reveal that the offshore grid is over-dimensioned. Rationalizing the grid by reducing transmission capacities to more realistic levels will give a more cost-effective solution. This was demonstrated by performing a quick simulation and analysis of a scenario featuring such a rationalized grid. Wind power will cause more frequent variations in hydro power generation, due to balancing needs. Parts of the increased variability in the hydro generators can be explained by the increasing amount of wind power in the system, while other parts are most likely caused by limitations in the simulation model itself. Conclusion: Given the number of assumptions made in the grid, in cost calculations and in the model at large, it is more important to focus on general trends than on concrete numerical values. However, it is clear that increasing the amount of on- and offshore wind power in the European power system will have a beneficial impact to society's energy costs. It is also clear that wind power has the potential to dramatically reduce CO2-emissions caused by power generation. The offshore grid seems to be more beneficial to the power producers than to consumers since it causes slightly higher energy prices and providing a measure of flexibility as to where offshore wind power production is sent. Wind power will present challenges, especially regarding transmission grid development. A sufficiently dimensioned grid will be essential to the successful implementation of such amounts of wind power, both with respect to profitability and in order to avoid waste of potential wind or hydro energy.

Reducing grid harmonics and increasing grid stability are both major issues for the operation of rail vehicles. For stability investigation of complex power systems, simplified system models are in need in order to reduce the model complexity and the simulation time. In this thesis work the effect of modelling a voltage source converter (VSC) for traction power system with and without the detailed pulse width modulated (PWM)-switch model is modeled. Effect of different operating conditions for the switching model on the harmonic content of the system is also analyzed. The same disturbance is imposed for the two models and the low frequency oscillation of the DC- link voltage response is compared and analyzed. The effect of semiconductor switching on the stability limit of the system is also investigated. Furthermore, the performance of a PWM time delay compensation technique during transient is analyzed. The result shows that in the model including the switching the DC- link voltage oscillation is damped and has a better stability margin compared to the average model. In the detailed switching model a converter loss is included while in the average model a no loss ideal case scenario is considered. As far as the switching harmonic is considered, the switching model with an operational condition of a high switching frequency and a switching frequency with an integer multiple of the fundamental frequency has a low harmonic content on the system compared to the operating condition of a low switching frequency which is not integer multiple of the fundamental frequency. A unipolar voltage switching technique has also a tremendous advantage over the bipolar voltage switching technique as far as this harmonic content in the system is concerned. Using a unipolar voltage switching technique reduces the harmonic content in the overall railway system. For triangular carrier modulators, an average time delay from the reference voltage to the actuated PWM terminal voltage of half the switching frequency is assumed .The delay in DC- link voltage control loop caused by the switching dead-time effect was improved by compensation of dead-time in the inverse-park transformation block of the control loop. The comparison of the compensated and non-compensated model proves that the compensated model is better in terms of the overshoot of amplitude of transient.

In order to comply with governmentally announced greenhouse gas emission reductions goals and to consolidate an independent and stable electric power and energy supply, Norway must increase its installed renewable energy based power generation capacity. Profitability estimations, today’s available technical solutions and regulations concerning preservation of natural resources leave construction of new small hydro power plants behind as the most plausible alternative together with construction of wind farms. Global trends such as technologic development and progress and the public opinion indicate that future wind farms in Norway will be located offshore. The assumption is supported by the recent handing out of a concession to an offshore wind farm project for the first time in Norwegian history. The projects name is Havsul 1 and the licence involves construction of 350 MW offshore wind power. Havsul 1 will be located in Mid-Norway, which is the region in Norway where the Norwegian Transmission System Operator (TSO) Statnett is most concerned about their ability to execute their task of assuring safety of power supply in the future. The concern owes to lack of generation capacity and transmission constraints. Experience show that commissioning of large offshore wind farms will impose power balance associated challenges on the TSO. By applying a slightly modified model developed by Sintef of the Nordel synchronous system in the power simulation tool DIgSILENT PowerFactory, grid connection of 350 MW and 1000 MW offshore wind farms to a bus bar representing Mid-Norway were investigated, targeting reduction of frequency excursions. To execute the reduction task, a so-called centralised Load Frequency Control (LFC) scheme was implemented and four hydro power plants were designated to provide regulating power pursuant to a priority key that used their response times as input. To simulate power fluctuations in the time span of hours, real time wind data acquired from the Danish offshore wind farm Horns Rev 1 was used as input in the offshore wind farm model. These data were kindly provided by the Swedish power company Vattenfall. The power fluctuations simulations showed that LFC is a well-fitted tool for bridling frequency excursions in the Nordel synchronous system caused by fluctuating power generation in an offshore wind farm. During the power fluctuations, which were of a particularly challenging kind, the system frequency complied with Statnett’s normal operation requirements of 50 ±0.1 Hz. The results weren’t too surprising since LFC has been used successfully in Europe for many years. They did however show that the amounts of the so-called frequency controlled normal operation reserves in Nordel may need to be expanded in case of a massive expansion in wind power in Norway. Fault Ride Through (FRT) investigations were also conducted by introducing 3-phase short circuit faults at selected bus bars. The simulations showed that the FRT requirements in Norway were not violated even in the worst case simulations. Some choices regarding the setup of the model may have exalted the simulation results.

The work consists in developing a power conversion unit for solar panel connected to the grid. This unit will be a single phase inverter in the low power range (24/48 V - 100/200 W), with digital control and without a DC-DC stage. The final system should be suitable for laboratory work. This master project will be complete, starting with a detailed specification of the project and finishing with an experimental validation.

Characterization of Epoxy (diglycidyl ether of Bis-phenol A cured with Tri ethylene Tetra amine) without fillers was done. The Water absorption test at 95°C shows that at saturation the epoxy contains a water concentration of 2.089%. The diffusion coefficient of absorption is calculated as 0.021 cm2/s. The diffusion coefficient of desorption is calculated as 0.0987 cm2/s. The diffusion is almost 5 times faster than absorption. Also the material looses weight as the hydrothermal aging progresses. The water in the sample leads to chain scission which leads to the weight loss. The weight loss is more incase of absorption followed by desorption than only absorption. The chain scission leads to decrease in the mechanical strength by around 45%. The diffusion of water from the samples doesn’t affect the mechanical strength of the materials. The glass transition temperature reduces by 20°C with water inside the sample. The diffusion of water out of the sample only increases by around 10°C. The Dielectric response of the material shows that after the water absorption the sample shows high losses at lower frequencies. Also the increase in the real part of the permittivity increases with low frequency. The rapid increase in the real art of the permittivity of the material at lower frequencies can be attributed to a polarization at the electrode due both to accumulation of the charge carriers and to chain migrations. The breakdown test of the samples shows that with water in the sample the breakdown strength of the material decreases by 10 KV, but the material regains its dielectric strength when the water is diffused out. This shows that the chain scission and weight loss of the samples has no or minimum effect on the dielectric strength of the sample

This report is divided into six main chapters. It starts off with an introductory chapter explaining the different propulsion strategies that have been considered during the last semester, and the final propulsion system that has been decided upon. The final propulsion strategy has several demands when it comes to components that have to be implemented and what type of components they should be. The main purpose for me in this project was therefore to meet these demands. Main demands for me were to demonstrate different possibilities when it comes to controlling the lights in the PureChoice vehicle, and to make sure the vehicle had enough energy stored in alternative storage devices in order to have a fully functioning system when it comes to driving the vehicle and managing the safety system onboard. The report continues with five individual chapters explaining how these demands were solved and which components that have been considered and implemented in the final vehicle. All off the chapters start of with an introduction about the topic at hand. They then continue with an explanation about the different components used in the vehicle, and reasoning for why exactly these components were chosen. In order to determine how the components would function in the final propulsion system, laboratory tests were performed on all the involved parts, and these laboratory tests are described at the end of all the chapters. This report includes both theoretical calculations and practical solutions.

Summary Literatures on battery technologies and diagnosis of its parameters were studied. The innovative battery technologies from basic knowledge to world standard testing procedures were analysed and discussed in the report. The established battery test station and flowchart was followed during the battery test preparation and testing. In order to understand and verify the battery performance, the well established test procedures developed by USABC (United States Advanced Battery Consortium) and FreedomCAR were reviewed. Based on the standard battery test flow diagram, battery test procedures are mainly categorised as below; 1.Test plan and pre-test – readiness review 2.Core performance test – charging, discharging, power, capacity and other special tests 3.Life cycle/ageing test – accelerated ageing, calendar life, abuse and safety Commercial battery testers were used to carryout the core performance test but electrochemical impedance spectroscopy (EIS) was employed for life cycle test and also to investigate the state of health (SOH) and state of charge (SOC) of the battery. The standard test bench as shown below was used for the experiment under the scope of this thesis. Figure 1: Standard battery test station Study on impedance based modelling of battery and laboratory experiment to measure the impedance was carried out. Electrochemical impedance was measured by applying an AC potential to an electrochemical cell and measuring the current through the cell using the shunt in series where battery voltage was measured directly from the terminals as shown in figure 1.Commercially available battery sensors were used to measure the current, voltage and temperatures. Impedance was calculated internally and observed on computer through the battery test program and also observed on Nyquest plot where real part is plotted on the X-axis and imaginary part on Y-axis at one frequency. A typical impedance spectrum of a Li-ion battery tested in the laboratory at 250C is presented below. This figure shows the measured impedance for different state of charge (SOC) without dc excitation current. Figure 2: Impedance Spectra of a Li-ion battery At real impedance Re(Z)  42 m, the real axis intersection of the impedance spectra was observed in the figure 2. For lower frequencies, all spectra show two semicircles. The first semicircle is comparably small and slightly depressed, whereas the second one is larger, nearly non-depressed and grows remarkably with decreasing state of charge. Finally, at the low-frequency end of the depicted spectra, the diffusion impedance becomes visible. At high states of charge, the diffusion impedance shows a 45°-slope, which is typical of Warburg impedance (state of diffusion at certain frequency).

Power system simulations, power market analysis as well as power system security and reliability analysis now serves as fundamental analysis tasks in power system planning and operation. Thus, it is very useful to discuss techniques, data needs and methodologies related power system reliability. Work is very important both in terms of operational and economical aspects of a modern power system. The task of determining the reliability of a given power system can be a complex and difficult process. Several methodologies exist and the terminology describing these calculations may differ from case to case. The work performed in this thesis demonstrates a known reliability methodology related to a real-life power system. In the latter, PSS®SINCAL and its reliability module ZUBER has been emphasized. The development of a working test model has been an important part of this thesis. In the latter, statistical information describing the power system has been the main challenge, both in terms of availability and quality. The various reliability data have been calculated from annual failure statistics collected by Statnett and experience data from Siemens. The scope of the reliability analysis was to determine the affect of future load expansions. It is a known fact that load development can affect the reliability of the power system and potentially increase the frequency of supply interruptions causing higher CENS costs. However, this was not the case as the changes in frequency of supply interruptions were insignificant. The results showed a suspected CENS cost increase of 1.6 NOK. Thus, it is evident that this is due to the fact that the uninterrupted power is now substantially larger. The reliability analysis show that the given power system will sustain its high level of reliability even with the planned load expansion. A comparative analysis of the ongoing development of a methodology (SAMREL) incorporating power market analysis via power flow and contingency analysis and PSS®SINCAL have also been presented. Comparing tools describing probabilistic reliability are important and can act as an incentive for future development of reliability tools. The major strength of PSS®SINCAL compared to SAMREL is simply the fact that PSS®SINCAL is a developed and commercialized tool. Unfortunately it was not possible conduct a reliability analysis using SAMREL, which was a major draw-back as a comparative analysis of both the tools relates to the same test model would have been very beneficial. SAMREL is comprised of several existing tools and therefore rely on the interaction between these tools, which after my opinion further complicate both the user friendliness and process of commercialization. From an educational point-of-view, the work related to SAMREL has several benefits contributing to increased general knowledge about power system reliability. It is evident that the accuracy of any reliability analysis depends on the quality of the statistical data. The studies show that local statistical data e.g. data based on local knowledge or local statistics often pose as a better solution. However, such data are unfortunately often very difficult to obtain, leaving no alternative as to use the available more general data. However, it is evident that some uncertainties always will exist but need to be taken into consideration when conducting such analysis. However, close cooperation with the utilities in combination with the utilization of high quality reliability data will after my opinion have a positive affect on the accuracy of the reliability analysis. Another important subject related to reliability is the process of identifying the critical system components. As shown, the main tool presented in this thesis is the consequence matrix, which categories the results obtained from the reliability analysis. The categories indicate both the consequence and the corresponding probability. Such matrixes need to be the result of a joint effort from both the customer and the professionals performing the criticality analysis, including all relevant information needed to classify criticality. The strength of this method lies in the fact that the defined probabilities can be used to identify large elements, such as substations and then be further utilized on a component level for the critical substation. The methodologies describing power system reliability have been emphasized throughout this thesis. The given test system and the performed reliability calculation demonstrates PSS®SINCAL as a tool for determining the reliability of a power system. The methodology utilized in this report is from the author’s point of view a good representation of a state of the art reliability analysis.