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.

The European Union has set a binding target saying 20 per cent of their energy consumption shall come from renewable energy sources within 2020. Around 4 per cent of the total amount is planned to come from offshore installations (40 GW). There total amount of planned offshore wind capacity is as of today 37 GW, mainly installations in the North Sea. The technologies that will be used for transporting the power to the shore are either HVAC technology using XLPE cables, transistor or thyristor based HVDC systems or HVAC Gas Insulated Line (GIL) technology. However, as the different technical solutions all have advantages and disadvantages compared to the other, the size of the power plants, distances from the shore and closeness to other wind parks will decide what technology will be used for the different cases.

This Master's thesis investigates a new application for the matrix converter: Shunt reactive power compensation. The suggested Matrix Converter-based Reactive power Compensation (MCRC) device is composed of a matrix converter, which input is connected to the grid and an electric machine at the output of the converter. The reactive power flowing in or out of the grid can be regulated with the matrix converter by controlling the magnitude and/or phase angle of the current at the input of the converter. The matrix converter has no bulky DC link capacitor like traditional AC-DC-AC converters. The thought electric machine is a Permanent Magnet (PM) synchronous machine which is compact as well, yielding an overall compact device. The main focus of the thesis is to evaluate the reactive power range that the MCRC device can offer. The reactive power range depends mainly on the modulation of the matrix converter. Two different modulation techniques are studied: the indirect virtual space vector modulation and the three-vector-scheme. The indirect space vector modulation can provide or draw reactive power at the input of the matrix converter as long as there is an active power flow through the converter that is different from zero. For pure reactive power compensation the indirect space vector modulation cannot be used and the three-vector-scheme must be used instead. Both modulation techniques are presented in details as well as their reactive power compensation range. To verify the reactive power capabilities of the device, three different simulation models are built in MATLAB Simulink. The first simulation model represents the MCRC device with the matrix converter modulated with the indirect space vector modulation. The second model represents also the MCRC device with the matrix converter modulated with the three-vector-scheme. In both model the PM machine is represented by a simple equivalent circuit. Simulations done with both models show a good accordance between the theoretical analysis of the device and the experimental results. The last simulation model features a simplified version of the MCRC system connected to a grid where a symmetrical fault occurs. The MCRC proves to be efficient in re-establishing the voltage to its pre-fault value.

In this thesis a feasibility study of a direct AC-AC converter for wind power application has been performed. Two three-phase voltages are converted to a single phase square wave for input to a high-frequency transformer and then rectified. No DC-capacitor is present in the converter and bi-directional switches consisting of two reverse blocking IGBTs allow the direct AC-AC conversion. Efficiency, silicon usage, price and output quality of the converter were to be compared with a reference case and conclusions to be drawn from the obtained results. The price comparison could not be finalized due to lack of price data. The efficiencies were found to be 97:7 % for both the converter setups while the silicon usage was 4:6 % lower for the direct AC-AC solution. A back-to-back converter was used as the reference case. The harmonic content was less in the back-to-back converter and DC-offsets in the phase currents caused power oscillations for both converters but they were higher in the direct AC-AC converter. The reference case needs more switches than the direct AC-AC solution if put in a split drivetrain configuration and DC-capacitors are also present in the former. The size is therefore expected to be lower for the AC-AC solution. The obtained results was used to conclude that the direct AC-AC solution is a feasible solution for a split drivetrain configurated wind turbine with multiple generators. The voltage of the square wave in the direct AC-AC converter needs to be two times higher than the DC-voltage in the reference case to obtain the same rated voltage in the generators when they are supplying power simultaneously. The switch voltage ratings must then be increased accordingly. Another application was proposed to better exploit the converter topology examined and to avoid the doubled voltage rating. An isolated power system with a time varying energy source such as a wind turbine needs an auxiliary power source to be able to supply the full load power when the other is unavailable. The double input converter can then control the two generators so that a constant output power is achieved. The square wave voltage amplitude can then be dimensioned from the load power only rather than for the total rated power in the two generators. It is therefore halved and the voltage stresses on the switches are similarly reduced.

Denne diplomoppgaven er skrevet i samarbeid med Statnett. Naturkraft har under bygging et gasskraftverk på Kårstø i Rogaland. Dette er et såkalt combined-cycle-kraftverk (kombinert kraftverk), som består av en gassturbin i kombinasjon med en dampturbin. Gasskraftverket vil kunne bidra med 418MW inn i sentralnettet, og det er Statnetts ansvar at kraften levert til forbrukerne har god nok kvalitet. Oppgaven tar først og fremst for seg problemstillinger knyttet til dynamisk respons og transient stabilitet i forbindelse med kraftverket. Statnett har bidratt med datamodell over nettet i Sør-Norge, og analyseverktøyet PSS/E er benyttet for å analysere kraftverkets respons ved ulike hendelser. Spesielt er det sett på regulerresponser ved frekvens- og spenningsendringer i nettet og kraftverkets egenskaper ved kortslutning. I tillegg er konsekvenser ved utfall av kraftverket analysert. Analyseresultatene er sjekket opp mot de relevante krav gitt i Veiledende systemkrav til anlegg tilknyttet regional- og sentralnettet i Norge (VtA) og Nordic Grid Code (NGC). Det er av interesse å sammenligne responsen i gasskraftverket mot den i et typisk vannkraftverk. Av den grunn er det lagt til en modell av et vannkraftverk på samme sted som gasskraftverket. Foruten at forskjellen mellom gasskraftverket og vannkraftverket er analysert er det også benyttet to forskjellige turbinregulatormodeller for gasskraftverket: en enkel modell beregnet på gassturbiner, og en mer avansert modell beregnet på nettopp kombinerte kraftverk. Det viser seg at den avanserte turbinregulatormodellen er den som egner seg best til simuleringer opp mot gasskraftverket. Skal man benytte den enkle modellen må man være obs på hvilket utgangspunkt man har, og hvilke hendelser man simulerer på. Spesielt ved fall i frekvensen kan ukritisk bruk av den enkle modellen gi et for optimistisk resultat. Gasskraftverket har problemer med fullstendig å overholde kravene gitt i VtA til drift under frekvensavvik, og simuleringer viser at responsen til magnetiseringssystemet er for kraftig. Kraftverket viser imidlertid god oppførsel ved feil i nettet, og bidrar til å gjenopprette spenningene i området etter feil. Ved normal drift tåler nettet et utfall av kraftverket godt, mens man ved svekkelser i nettet kan oppleve til dels lave spenninger etter et utfall.