<p>Several inverter topologies for use with power conditioning of photovoltaic modules were investigated with both national and international requirements in mind, as well as also practical challenges and the ability to be user friendly for ordinary people. A good inverter topology should also be low cost, have a high efficiency and have a good output power quality. In addition several filter possibilities was investigated, and it was concluded that the LCL-filter was the best for the given conditions, since it attenuated the unwanted frequencies the best with relative small filter parameters. Five different inverter topologies was then presented and investigated: A hybrid multilevel inverter, a full bridge inverter, a series resonant buck-boost inverter, a flyback converter with unfolding H-bridge inverter and a series resonant converter with unfolding H-bridge inverter. After an investigation of the above mentioned criteria, two of the inverter topologies, the H-bridge inverter and the hybrid multilevel inverter, were considered better than the rest for the given requirements and purposes. These were then closer analysed with the computer simulation programs SIMULINK and SPICE in order to find quantitative arguments about which topology was the best under the above mentioned conditions. Filter parameters were also quantified. From this it was found that the hybrid multilevel inverter was 0.5 to 1 percent point more effective than the H-bridge, at the same time the total harmonic distortion was significantly better, approximately five to ten times better than the H-bridge inverter’s total harmonic distortion. This means that the hybrid multilevel inverter may have a considerably cheaper filter. Both of these factors contributed so that the hybrid multilevel inverter was regarded the better topology and this topology was selected for further tests. The last simulation was about finding good switches to equip the hybrid multilevel inverter with. Here it was found that the decisive factor for the low voltage bridge was quick switches, whereas for the high voltage bridge it was more important to have switches with low resistance when turned on. The chosen switches were STY60NK30Z and BSC520N15NS3 G for the low voltage bridge. In addition it was meant to perform a laboratory experiment with the selected topology, but because of a delay with the deliverance, the test object did not arrive at time, so the experiment could not be done.</p>

<p>The General Purpose 2D Electromagnetic Tool, GP2DET, at Voith Siemens Hydro Power Generation GmbH is a tool developed for simulation and calculation of electrical parameters in large hydro power machines. In this tool, the stator windings have been modelled as massive conductor blocks, and current has been impressed on these conductors as current density for load situations. The scope for the work in this thesis has been to implement an automated procedure for a detailed modelling of the stator windings, testing of the procedure and analyses of losses from eddy currents and circulating currents. A group of macros was written in ANSYS APDL for the reworking of existing simulation models. The macros automatically rework models created in GP2DET, and replaces massive stator conductors with detailed stranded conductors. 17 alternatives for which conductors that shall be replaced were implemented. Bar- and coil windings are supported, and bar windings can be modelled with Roebel-transposition. Some detailing alternatives allow replacement of coils or coil groups. For these alternatives, automatic connection of each strand in the stranded coil sides is carried out. All strands are connected uniquely within a coil, and can be connected blockwise between coils and coil groups if desired. Transposition is available within a coil, between coils, and between coil groups. One type of transposition was implemented. The 17 detailing alternatives were tested on three different machines; two with bar windings and one with coil windings. For these machines the procedure executed faultlessly.</p>

<p>This Master thesis studies losses in superconductors. Losses arise when the superconductor carries alternating current or is placed in an alternating magnetic field. As most power applications involve at least one of the two, loss mechanisms and magnitudes are important when examining the possibility of making superconductor systems competitive to conventional power systems. There are two parts to the task at hand. The first part is a literature study on superconductivity and AC losses in superconductors. A division between two general types of superconductors is presented; type I and II. The Bean model for AC losses in type II superconductors is described, together with equations giving the power law between generated losses and applied magnetic field. In the Bean model, the losses are proportional to the applied field cubed below a limit called the penetration field. Above it, the exponent changes to one. Losses due to coupling of filaments are also treated. The measuring setup used in the AC loss experiments is calorimetric, and the principle behind the method is presented. The superconductor used, magnesium diboride (MgB2), is introduced. The literature study is concluded with short résumés on other AC loss studies done on MgB2, and studies done on one type of high temperature superconductor. The second part is measuring AC losses due to an applied alternating magnetic field in two superconductor samples from different manufacturers. Specific information on the two samples, details on the measuring system, preparations and the measuring procedure is described. The logged data and equations used when processing the results are also listed. Measurements have been performed at six different temperatures; 25, 28.5, 30, 31.5, 35 and 45 K. The magnitude of the applied magnetic field was varied between 3 and 150 mT. Both parallel and perpendicular field directions were applied. Generated losses lead to a temperature increase in the superconductor. The rise in temperature was detected as increased resistivity of a thin copper wire glued onto the sample, as the copper resistivity is temperature dependent. The obtained results are examined in double logarithmic (loglog) and normal axis diagrams, where the main aim is to find loss slopes and penetration fields at the different temperature levels, and to compare these to the Bean model loss equations. In addition, the results are compared to theoretical loss equations for cylindrical conductor geometry. This is done in order to look at the accuracy of the fittings and to compare the penetration fields obtained here to the ones found in loglog diagrams. The results have also been compared to various studies on MgB2 and other superconductor types. The measured loss slopes at fields below the penetration field, found from loglog diagrams, do not fit the Bean model. The slopes are here lower than the applied field cubed. At fields greater than the penetration field, losses are proportional to the applied field, as in the Bean model. Two reasons for the deviations have been discussed; measuring errors and losses being coupling losses. Even if the measuring errors may be considerable due to human reading errors, they would have to be systematic for the losses to fit the Bean model. This is the reason why measuring errors are seen as unlikely to be the grounds for the non-fitting results. The results do also not fit the coupling loss slope and as only one field frequency has been used, the obtained results are not enough to support or reject this theory. Due to the deviation from the Bean model loss slopes the curve fittings to the cylindrical conductor loss equations were mostly poor, as they have the same loss slopes as the Bean model. The penetration fields found from loglog and normal axis diagrams and the curve fitting are not equal. It is establish that the ones found from loglog diagrams should be used. Two of the other studies done on MgB2, which have been summarised in the thesis, fit the Bean model, and the last case did not. The authors found no explanation to the non-fitting results, and have ruled out coupling losses as a viable reason. Studies on the other type of superconductor also represented both cases. Here, some non-fitting results were explained by coupling losses. When comparing loss magnitudes, only one of the samples used in these experiments had as low results as found in two other studies.</p>

<p>This master thesis was executed at the Department of Electrical Power Engineering at the Norwegian University of Science and Technology (NTNU). The thesis was initiated to establish and evaluate an alternative model representation of the facility at Ormen Lange. Traditionally, a PQ-model has been used to represent Ormen Lange. This thesis, however, has implemented three two-terminal dc line models (converter models) to represent the facility. The first part of the thesis starts with an overall introduction to the basic principles of configuration, operation and control of HVDC systems. The objective of this part is to provide an overview of the HVDC technology which is treated in detail later in the thesis. The software tool “Power System Simulator for Engineering” (PSS/E) was used for both power flow and dynamic simulations performed in this thesis. The second part of the thesis describes the power flow establishment, and constitutes the basis for both power flow and dynamic simulations. The main focus in this part is the modeling of the two-terminal dc line model which is implemented at Nyhamna. Data for the two-terminal dc line model is presented on three consecutive data records. Since these data enables not only power flow analysis but also establishes the initial steady-state for the dynamic analysis, a detailed description is presented in this section. The latter data is based on technical information provided by ABB and default values in PSS/E. The third part of the thesis presents the power flow simulations. The objective of this part is to gain knowledge about the performance of the two-terminal dc line model implemented at Ormen Lange. This knowledge facilitates the understanding of the following dynamic simulations. Two cases were studied to simulate the action of the converter control system when exposed to a depression in rectifier bus voltage. In the first case the rectifier transformer tap settings were adjustable. In the second case the rectifier tap settings were locked to its initial value. The purpose of locking the tap setting was to represent a transient situation where the tap changer action is too slow and hence not considered. The result showed that with adjustable rectifier tap settings, the depression in rectifier bus voltage is handled by reducing the rectifier transformer tap position and firing delay angle. This increased the voltage on the valve side of the rectifier transformer and enabled the rectifier to maintain dc current control. Consequently, the scheduled dc values were unaffected by the depression in rectifier bus voltage. However, with the rectifier tap setting locked, the transformer did not boost the voltage on the valve side of the rectifier transformer. This caused the control logic to reduce the rectifier firing delay angle to its minimum, and the inverter assumed control of the dc current. With the inverter in control of the current, the scheduled dc current was reduced by a fraction equal to the current margin along with the remainder dc values. Hence, the presence of an adequate rectifier transformer setting is essential for the two-terminal dc line model to maintain scheduled dc values during voltage depression. All simulations showed that a voltage depression at the rectifier bus leads to a reduction in rectifier reactive power consumption. This is due to the action from the control logic which reduced the rectifier firing delay angle to counteract the voltage depression. The greatest reduction in rectifier reactive consumption was experienced when the rectifier firing delay angle was reduced to its minimum value. Hence, in situations with depressed bus voltage, the latter operation of the converter control logic causes the two-terminal dc line model to exhibit less stress to the ac system than the PQ-model. The fourth part of this thesis contains a detailed description of the dynamic modeling of the two-terminal dc line model (CDC4T). Many of the chosen parameters are based on an example in [15], and do not necessary represent realistic values. The final part of this thesis presents the dynamic simulations. The objective of this part is to analyze the control actions of the CDC4T model under normal regulation and during temporary overriding the normal regulation. This was performed by introducing ac system faults which depressed the rectifier bus voltage to a varying degree. Further, this part analyzed the consequence of using the dynamic model CDC4T to represent Ormen Lange instead of a PQ-model. The purpose was to determine whether the response from the ac system differs when using the CDC4T model instead of a PQ-model. It is important to emphasize that this part does not evaluate stability issues associated with the implementation of CDC4T. The results from the dynamic simulations showed that CDC4T exhibited an instantaneous response to changes in rectifier ac voltage. This is because CDC4T is a pseudo steady-state dynamic model which omits the L/R dynamic of the dc system and high frequency firing angle controller dynamics. Further, the results revealed an important characteristic of the CDC4T model. After fault clearance, the rectifier bus exhibited small voltage fluctuations. The rectifiers compensated these fluctuations by adjusting their firing delay angles correspondingly. Consequently, the latter resulted in fluctuations in reactive power consumption. This means that the ac system perceives the CDC4T model as a varying reactive load following fault clearance. Comparing the ac system response when using the CDC4T model and when using the PQ-model, the results showed that the main difference was CDC4T’s generation of reactive power fluctuations. These fluctuations were experienced in the transmission line going into Nyhamna and Viklandet, and were substantial compared to the initial loading of the transmission lines. Two arguments were used to substantiate why the response from the CDC4T model only differs from the PQ-model in terms of reactive power fluctuations: I. The calculated value of the short circuit ratio at Nyhamna indicated a strong interconnected ac/dc system. II. The dynamic behavior of the pseudo-steady state model, CDC4T, is limited. Both the L/R dynamic of the dc line, smoothing reactors and high frequency controller dynamics are omitted. In further studies where converter modeling at Ormen Lange is considered, a more complex dynamic dc model should be utilized to represent the converters. This model should include L/R dynamic of the dc system and high-speed controller dynamics, and will thus influence the ac system to a greater extent than CDC4T. Further, the model establishment should focus on achieving a sufficiently realistic load representation of Ormen Lange. In this manner, the converters’ influence on system stability can be evaluated.</p>

<p>Sub sea compression for maintaining reservoir pressure in a gas field is important to have a steady production of gas as it is extracted from the field. Electrical drives in the several megawatt range are suitable to control the compressor motor since it is not desirable to have gears which need maintenance. Problems related to the location on the sea bed have so far been overcome by using massive pressure tanks which hold 1 atmosphere. A new approach would be to allow the pressure on the sea bed to be applied on the electrical components. This will reduce and simplify the system only needing a thin walled casing filled with oil to contain the electronics, but the electronic components then need to be compatible with the oil and function at high hydrostatic pressure. This report include suitable electrical power systems for a compression application, theory around the most likely to be used switch, some available modules and an experimental set up for testing IGBT compatibility with oil. Converters consisting of rectifiers and inverters are widely used in industrial motor drives and it is assumed that such a converter will be used consisting of a diode bridge rectifier and a neutral point clamped inverter. High voltage applications often operate with voltages above the rated value of many semiconductor components which means that switches must be series connected. A neutral point clamped inverter with series connected switches will be able to handle the high voltages and produce a good spectral output to the motor terminals. The switches used in the inverter will probably be IGBTs. The IGBT evolved as the most successful device for high power, high switching frequency applications blending MOSFET switching capabilities with BJT on-state conduction properties. Development has produced a lot of versions of this kind of switch, and by modifying doping profiles and geometrical properties a set of devices with improved characteristics has been made. Packaging techniques make it possible to integrate the switches in different environments. Examples are the press pack modules which can be hermetically sealed and the standard DBC solutions. To test compatibility with insulating oil, an experiment was set up. An IGBT inverter leg module was placed inside a tank which was filled with oil. The module was operated in an H-bridge configuration with another bridge leg on the outside of the tank. Thorough testing before submerging it was performed to ensure and document normal behaviour. When fully submerged the module was tested and the results compared with those from the initial testing. Short duration of continuous switching was also performed followed by intermittent operation with current pulses and long term continuous switching. None of the captured scope pictures or temperature measurements showed deviation from normal IGBT behaviour or change of characteristics. It can then be concluded that when submerging an IGBT module in insulating oil, no instant failure or change of electrical behaviour occurs.</p>

<p>The goal of the master thesis is to design, dimension and construct a power boost system for the drive trains in electric vehicles, utilizing supercapacitor technology. In order to build the system a supercapacitor bank and a converter has been constructed. The system has been designed to be used in the new Think electric vehicle, and each part of the converter has been dimensioned according to information provided by Think Technology. The master thesis is limited to the design and construction of the power boost system, and the implementation, interfacing and control of power sharing have not been dealt with. The supercapacitor bank and the converter are built based on analytical computations and simulations. The supercapacitor bank can store up to 100 Wh and is built from 90 series connected cells rated 1500 F each. The bidirectional DC –DC converter is based on a standard intelligent power module with three legs in a bridge configuration and three inductors. An interleaved switching sequence is selected for the operation of the legs and each IGBT is capable of switching 150 A at 600 V. The thermal management of this module is solved with the use of a heat sink with fans for forced air flow. The inductors are made from amorphous alloys and copper foil, achieving an inductance of 0.25 mH and a maximum current rating of 100 A. Voltage smoothing capacitors and measuring devices have also been implemented in the converter design. The results presented are held to be accurate, all though measurements gathered are affected to a certain degree by noise in the system. Based on tests of the various components, it is concluded that the power boost system is an up to date system and has achieved the design goals of delivering 30 kW for 12 seconds. Some tests are yet to be completed in order to make sure that the system works in continuous operation. Further work based on this master thesis should include more extensive testing on the system, and perform an optimization of the supercapacitor bank and the inductors. The intelligence for optimized load sharing must be created, and a communication interface with the power control unit in the Think electric vehicle must be made.</p>

<p>In this master thesis the basic theory of grid connected photo-voltaic systems is explained, giving an introduction to the different aspects of system design. Starting with a look at the standards concerning grid connection of distributed resources, and working its way through how the photo-voltaic cells work, to how photo-voltaic modules with electrical converters can be arranged. Some different converter topologies suitable for use with photo-voltaics are found, and based on these topologies, solutions for how to control these converters have been examined. These controls involve methods for utilizing the maximum power from solar panels, methods for synchronizing with the grid and methods for current and voltage control. Based on this theory a system model is made, including an isolated current fed full bridge DC-DC converter in cascade with a three phase full bridge DC-AC converter having a LCL filter as grid interface. This model is simulated in Simulink and experiments are made on a laboratory setup, where focus has been on the control system. Therefore linear system models of the control system has been made, and these have formed a basis for the optimization of the control systems. The simulations have been made using Simulink, and the control system for the converters has been implemented in two DSP’s, one for each converter. The design and construction of the DC-DC converter has been made in this thesis, but it showed out to be more complicated then first assumed. Because of this, too little time was spent in the design of the circuit and too much time was spent on testing and correcting errors. It ended with a non-functional converter, and therefore the experiments made had to be done without the DC-DC converter. However the report shows that the isolated current fed full bridge DC-DC converter is a promising topology in photo-voltaic systems, and should be investigated closer. It is found in the simulations and experiments made, that the system models derived give a dynamic response close to the real, and are suitable for giving a basic understanding of the system dynamics and for optimizing the control system. The control system consists of a maximum power point tracker which effectively finds the point where the photo-voltaic modules delivers the highest power, and in order to synchronize to the grid voltage a phase locked loop is used, which locks the converter output to the grid voltage in less then 10ms. In order to control the power flow into the grid, current control in a rotating reference frame locked to the grid voltage is used. This has simplified the control since it gives DC-values stationary, and has made it possible to separately control the active and reactive power flow. Most of the tests made in the simulations and experiments have been made with operating conditions close to ideal. In order to verify how the system handles varying operating conditions, and to see if it coincides with the requirements in the standards, more extensive testing should be made of the system. This includes testing with varying irradiance of the solar panels, grid disturbances and grid failures.</p>

<p>Nord-Norsk Vindkraft AS is planning to build two wind farms in Nordland, Norway. The wind farms are located at Sleneset and Sjonfjellet. The planned total installed power is 653 MW. An important part of the planning phase is to perform steady-state and dynamic analyses, to simulate the impacts from the wind farms on the existing power system in the area. The steady-state analysis is performed by Norsk Systemplan og Enøk AS (NORSEC). The project presented in this master thesis is part of the dynamic analysis. The overall objective for this project is to illustrate the dynamic impacts from the wind farms on the existing power system and the differences in impact depending on the various control strategies being used. The following elements are included in the assignment: - Establish a steady-state and dynamic grid model describing the power system in question. - Determine whether the wind farms are able to reach full production during different configurations without reaching an unacceptable operating state. - Examine the impact from and behaviour of transformers with load tap changers. - Illustrate the differences between different control modes in the wind farm connection point. The model used in this project is established by converting the steady-state model used in the steady-state analysis from Netbas to SIMPOW. The time in the steady-state model is set to January 2009. The steady-state model is then expanded by introducing aggregated doubly-fed induction generators for power production in the wind farms. For some of the simulations, a static VAR compensator is inserted at Bardal. The dynamic model is established by introducing a dynamic description of the components in the steady-state model. Due to lack of dynamic data, typical values are used for some of the components. The comparison between the power flows from the basic model provided by NORSEC and the initial converted SIMPOW model show small differences in reactive power flow. These differences were, however to be expected, due to changes made when converting the model from Netbas to SIMPOW but are not considered important for the conclusions to be drawn from the project. Simulations describing an increase in wind power production from 50% to 100% are performed on the dynamic model describing the grid between Salten and Tunnsjødal. The timeframe of increase varies depending of the objective for the specific case. The simulations performed on the dynamic model indicate a need for reactive power compensation between the wind farms and the connection point at Nedre Røssåga. Without reactive power compensation on the radial connection, the wind farms are not able to reach full wind power production without breaching either voltage or thermal limits. This is the case even if local compensation is added at the wind farms. With an SVC in voltage control placed at Bardal, the wind farms are able to reach full power production without violating any specified limits. The SVC maintains acceptable voltage levels within the radial. However, the amount of imported reactive power at the connection point increases during the production increase. This causes a depression in voltage in the rest of the grid. If the SVC at Bardal is set to control the reactive power flow in the connection point, simulations indicate that the amount of reactive power drawn from the main grid can be considerable reduced. This, however, results in a larger need for reactive power production within the radial. A larger reactive power production increases the voltages. Without voltage control at the wind farms or voltage regulation by load tap changers, the simulations show that the voltage at the generator terminals increases above 1.05 pu. Simulations demonstrate that tap-operations in the transformer at the connection point between the main grid and the wind farm radial increases the amount of imported reactive power. This takes place when the SVC operates in voltage control. The need for reactive power production within the radial is then reduced. The tendency is the same whether voltage control is introduced at the wind farms or not. When the SVC operates in reactive power control and no voltage control is present at the wind farms, tap-operations from the same transformer result in an increase in reactive power production within the radial. However, if voltage control is included at the wind farms, tap-operations at the connection point will decrease the reactive power production. This is because in voltage control the wind farms are consuming reactive power in order to maintain a specified terminal voltage. The results from the simulations indicate that the number of tap-operations from the transformer at the connection point is reduced when the SVC at Bardal operates in reactive power control compared to when it operates in voltage control. However, no wind models based on statistics are introduced in this project. It is therefore uncertain to what extent a similar result would be obtained under more realistic conditions. All the simulations show that when the production from the wind farms increases, the voltages in the grid outside the radial decreases. This is due to increased reactive losses. The decrease is largest when the SVC at Bardal operates in voltage control due to reactive power drawn by the radial connection. The area in the main grid with the largest decrease is located between the connection point at Nedre Røssåga and Trofors. This project is only a part of the necessary dynamic analyses that have to be carried out in the planning phase for the wind farms at Sleneset and Sjonfjellet. A natural continuation of this project could be to perform analyses in a light load situation, and analyses of the system’s response to disturbances. Wind models obtained from statistical wind data should also be included in future dynamic analyses.</p>

<p>A new Klystron modulator is to be developed as a part of the new Linear Accelerator (LINAC4) project that is currently running at CERN. The Klystron modulator is required to supply a pulsed output voltage of -100 kV / 20 A with a repetition rate of 2 Hz and a pulse length of 800 us. In addition to this, the Klystron modulator must also handle arcing in the Klystron, and allow for no more than 10 J of energy to be dissipated in the arc in such a case. This thesis studies possible solid state based topologies that could be relevant for the Klystron modulator. A single switch topology, based on a 12 kV IGCT switch and a pulse transformer, is studied in detail and developed as a full scale prototype. Preliminary test results indicate that this will provide a satisfactory solution that meets the requirements. A second topology based on the Parallel Resonant Converter (PRC) was studied in detail through analysis and simulations. This showed to be a promising solution that could be an improvement compared to the single switch topology. The PRC is fully controllable and thus offers a flexible solution that can meet various demands. The topology also showed very good arc handling capabilities, and the PRC can be configured to protect the Klystron by its natural response.</p>

<p>Abstract Conventional induction heaters for extrusion purposes have an efficiency of only 55 – 60 % due to the resistive losses in the copper coils putting up the magnetic field. By using superconductor and DC current these losses can be minimized and the overall efficiency can be increased to as much as 90 %. DC current requires a new design of the induction heater were the billet has to rotate with the magnetic field perpendicular into the billet. A 200 kW induction heater is to be build by using the superconductor MgB2 which was discovered in 2001. The heater consists of two coils with 16 discs in each coil. Each disc has 75 turns inwards and 75 turns outwards with a total length of 550 metres wound in two layers. The operating temperature in the coils is 20 – 22 K and the current is 200 A. The discs in the coils have to be joined together in a resistive overlap joint. The joints will generate heat which must be cooled away and will decrease the critical current (highest current the superconductor can conduct). It is important that the joints have low resistance and can be made in fairly reproducible way. A tool to make these joints was therefore made and tested. The overlap joints had a length of 10 cm and had a resistance of maximum 71 nΩ. When increased the force pressing the conductors together the highest resistance was 48 nΩ which will generate 2 mW of heat each if a operating current is 200 A. The critical current was decreased due to the joints. The critical current was found to be 238 A at 30 K and approximately zero magnetic field density. The expected critical current for the joints are approximately 400 A at 25 K. With an expected reduction in critical current of 15 % due to the magnetic field in the joints can still conduct the operating current of 200 A with a large safety limit. To be able to determine the performance of the joints the temperature has to be measured with a certain degree of accuracy. This was a problem in the work with testing the joints and the accuracy of the thermometer itself had to be carried out. The thermometer was the temperature dependency of the resistance in a 0.1 mm copper wire. The deviation from the given resistance ratio increased at lower temperatures and caused a misreading of as much as 5 degrees at 21 K. It was determined that the thermometers are not recommended to use at temperatures below 35 K and that they need a calibration before use at higher temperatures if high accuracy is required. The superconducting tapes are insulated in polyimide film before they are wet-wound in an epoxy with high thermal conductivity. The insulation and winding of these discs have been going on in parallel with the joint testing and the process is described in this report.</p>