<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>

<p>Offshore wind power has an increasing interest in the research community and among the politicians. Therefore it is important to find the right solutions to meet the environmental and commercial requirements to give offshore wind power a promising future. This thesis are proposing a new converter topology for offshore wind parks. Since the topology is based on DC transmission in stead of AC transmission it is better suited for use in this type of parks. All the converters are located in the wind turbines and the turbines are connected in series directly connected to shore without any transformation stages. The one-phase AC to three-phase AC converter with the new switching pattern is explained and a method to calculate the losses in the converter is given. The loss calculation method is based on the characteristics of the switch found in the data sheet, which in this case is a RB-IGBT. The conduction losses, turn-on, turn-off and recovery losses for one switch are calculated and multiplied with the number of switches in the converter. An equation of the total losses per switch is given and there are performed loss simulations for the converter in PSCAD with good results. In the AC-AC converter there are bidirectional switches, in this case two reverse-blocking IGBTs. The RB-IGBT is compared to other types of bidirectional switches which is made of IGBTs and diodes in anti parallel. The comparison shows that with the RB-IGBTs the on-state voltage drop is halved since a RB-IGBT has the same on-state voltage drop as a normal IGBT. This also reduces the on-state losses. The architecture of the RB-IGBT is almost the same as the IGBT but with an extension of the p+ layer on the edges up to the gate isolation. This separates the sides from the active region of the chip so the leakage currents from the side surfaces of the device are blocked. A design of a high power high frequency transformer for the converter topology in the nacelle of the wind turbine is proposed. A design method is used and a program to calculate the necessary values is made. The transformer should be a double E-core with a centre leg of 4.5 cm made of the ferrite material N27. Both primary and secondary windings, which will be copper foils, should be wound on the centre leg of the core using a bobbin. The primary windings will be separated in two sections each section having 12 layers with two turns per layer. The secondary windings will be sandwiched between the primary sections and will consist of 24 layers with two turns per layers. Each foil conductor has a height of 4.5 cm and a thickness of 0.3165 mm. The new converter topology reduces the converter losses due to fewer converter stages, a new type of reverse-blocking IGBT and a new switching pattern. It also reduces the weight of the converter system because of no capacitors and a lighter transformer. This is important for floating wind turbines. A prototype of the converter topology with protection should be made to verify the results of this thesis. Simulation studies for the whole park during operation and faults should also be carried out to see if the topology fits the harsh conditions offshore.</p>

<p>This thesis has studied permanent magnet motors in electric vehicles (EVs) under the assumption that they are tractable due to a low weight and high compactness. The implementation has been investigated through a case study, which resulted in an EV simulation model. The model contains a maximal torque per ampere and a closed-loop field weakening controller. Abstract Faults are a special concern in permanent magnet motors. Fault sources and faulted behavior are addressed separately. The EV model was used to simulate faulted behavior. Abstract Two passive fault measures are suggested as the most attractive for propulsion purpose motors; these are shutting down the inverter and imposing a balanced short to the machine terminals. The balanced three phase short circuit showed a considerable transient behavior not seen during inverter shutdown. This results in an increased requirement to the inverter rating using the balanced short. Also, demagnetization risk of rotor magnets is higher under the balanced short. Abstract The maximal braking torque during inverter shutdown was high for the simulation model, and exceeded the braking torque of any fault. This concern led to a mathematical examination of the inverter shutdown, resulting in two equations that may be of use during design. The resulting equations are based on simplifications done in the literature, and show the relationship of the balanced short to the inverter shutdown.</p>

<p>Induction generators constitute 30 percent of today’s installed wind power. They are very sensitive to grid voltage disturbances and need retrofitting to enhance their low voltage ride through (LVRT) capability. LVRT of induction generators by shunt-connected FACTS controllers such as STATCOMs have been proposed in earlier studies. However, as this report concludes, in this application their VA-rating requirement is considerably higher than that of series-connected FACTS controllers. One such series FACTS controller is the magnetic energy recovery switch (MERS). It consists of four power electronic switches and a capacitor in a configuration identical to the single-phase full bridge converter. Its arrangement in an electric circuit, however, is different, with only two of the converter’s terminals utilised and connected in series. It has the characteristic of a variable capacitor and is related to FACTS controllers with series capacitors such as the GCSC and the TCSC. Successful operation of MERS for LVRT of induction generators has been demonstrated by simulations and verified by small-scale experiments. Index terms – Low voltage ride through (LVRT), magnetic energy recovery switch (MERS), series-connected FACTS controller, wind power, grid code, induction generator.</p>

<p>Offshore power transmission is becoming an increasingly important issue. To moderate climate change, world leaders have set environmental goals that will be very difficult to reach without renewable power production and the removal of production units with high emissions. Wind power and electrification have been the focus in this report. Plans for the expensive wind power are already moving offshore. This report has made an attempt at suggesting a guideline for well-suited transmission systems, for wind power projects located at a distance in order to make them more economically attractive. Another emphasis has been to find the most suitable transmission system for gas turbines at offshore installations. As expected, the use of alternating current is best suited at shorter distances. At longer distances this system is still feasible up to 350 km, but losses will be high and there will be limited power available. A conventional thyristor-based direct current system will therefore be an attractive option for high power ratings and long distances. On the other hand, direct current based on voltage-source converters is considered more expensive, but has an improved control of reactive power and is therefore preferable to the conventional direct current system. To determine which system has the best design, one has to consider each case individually.</p>