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.

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.

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.

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.

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.

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.

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.

A direct driven permanent magnet synchronous machine with concentrated windings is optimized with respect to system efficiency. The goal is to win the European Shell Eco Marathon Urban Concept group using a hydrogen fuel cell and an electric motor. Considerations such as on-board energy storage, a freewheel for coasting, winding design and connections are taken into account. The result is a machine with higher efficiency at all loads and an optimal operation point at cruising speed, obtaining 93% efficiency. Considerations for further improvements in both power electronics and motor design are presented, along with a new philosophy for making very slow PMSM CW machines with multiple phases, both yielding higher efficiency and smaller requirements to structural stiffness.

This master thesis is written at the Department of Electric Power Engineering at the Norwegian University of Science and Technology. The work has been carried out at NTNU in Trondheim. The thesis deals with configuration of large offshore wind farms and transmission systems, and is a continuation of the project written during the autumn 2008. Today several plans on 1000 MW offshore wind farms exists. The size of the wind farms has led to a challenge of how to find an efficient and secure design of the overall system. The system has to be cost-effective in order to compete with other forms of power generation. In this study, costs is not considered. The purpose of this thesis was to study different transmission systems and configuration of an 1000 MW wind farm located 75 km from shore. The optimal distance between the turbines is a compromise between wake effect, wind farm are and cable lengths. To perform a detailed study of wake effects and optimal spacing, computer programs like WindSim would be necessary. Three common wind farm configurations is radial, star and ring layout. The selection of layout depends on costs, wind data and the wind farm area. Various wind turbine systems have been developed and different wind generators have been built. According to the survey of different wind generator system and considering the grid connection requirements on wind turbines, the developing trends of wind turbine generator systems shows that variable speed is very attractive and concepts with full-scale power converters will become more attractive. In this thesis two wind farm configurations with different transmission system were further studied. AC/AC, AC/DC and DC/DC are possible transmission systems. In this thesis AC/AC and AC/DC were compared. The selected layout of the wind farm was the radial layout. Number of strings was 35, with eight turbines in each string. Each wind turbine could produce 3.6 MW, which gives a total generation of 1008 MW. The two configurations were modeled in PSS/E. Siemens has made a model called WT3 that was developed to simulate performance of a wind turbine employing a doubly fed induction generator (DFIG). The model was developed in close cooperation with the GE Energy modeling team. This model was used in this thesis. For the dc transmission the HVDC Light from ABB was used. Two different disturbances were applied. One at the connection point at shore, and one at the connection point for all the radials. The load flow results shows that the losses are 5.8$%$ higher in the AC/DC system. The dynamical result shows that both of the systems were stable, and fulfill the grid code requirements. The results indicates that the short-circuit MVA is higher in the ac system than in the dc system. After a fault the voltage recovery was more smoother in the dc system, and the voltage recovery time were shorter.

This master thesis has been written at the Department of Electric Power Engineering at the Norwegian University of Science and Technology. The work has been carried out at the Royal Institute of Technology in Stockholm, where the author spent the last year of his studies as an exchange student. In the thesis, six different designs of the electrical grid of a 540 MW offshore wind farm, placed 100km off the Norwegian coast, have been studied and compared. At this distance, AC cable transmission might be difficult because of the reactive power production in the cables. Taking this into consideration, two options for the transmission system to shore have been studied. In addition to the AC cable transmission, voltage source converter based HVDC transmission, in the form of HVDC Light, has been studied, giving a total of 12 models. The main scope of the thesis was to study the load flow situation and power system performance of the different offshore wind farm layouts. Two load flow cases were run for each model; the first studying the model when the active power transmission to shore was maximized, the second studying the model under a contingency situation. The reliability of the six designs was compared by calculating the expected number of cable failures during the life time of the wind farm for each design, and what consequence the disconnection of any cable would have on the power losses. In order to study the effect of the offshore grid design and transmission system design on the offshore power system stability, dynamic simulations have also been executed, and the voltage response and rotor speed response following a fault have been studied. All simulations have been executed in version 31 of the program PSS/E. The wind farm was modeled full scale, consisting of 108 wind turbines rated at 5MW. The wind turbines were modeled as doubly fed induction generators, using the generic wind model that comes with the program. The load flow simulations showed that an AC cable connection to shore gave lower total system losses than a DC connection for all designs. The lowest losses were found at the n-sided ring design in the AC/AC system, and the highest losses were found for the star design in the AC/DC system. These losses were 2.33% and 8.19% of the total installed capacity, respectively. In the dynamic simulations, a three phase short circuit fault, lasting 150ms, was applied at three different places in the system. The simulations showed that except from at the wind turbines that were islanded as a result of a fault, all dynamic responses were stable. The HVDC Light transmission to shore gave the highest voltage drops and the lowest voltage peaks offshore. Also, the maximum speed deviation was found to be larger when using HVDC Light transmission compared to using AC cables, with two exceptions; the radial and star designs when a fault was applied to the transmission system. A comparison of the six different grid designs showed that the results were varying. Based on the results in this thesis it has not been concluded that one of the offshore designs have better dynamic qualities than the other. The simulation results indicated that this is case specific, and more dependent on where in the offshore grid the fault occurs rather than the design of the offshore grid.