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.

To keep process-specificity while extending system boundaries hybrid techniques were developed allowing the micro structure of the important parts of a system to be revealed at the same time the entire economic system in which the system is embedded to be covered. Despite the substantial improvements bestowed by hybrid techniques some downsides still hold. Tiered hybrid LCA first does not model feedbacks whereas the relationship between the process-based system and the input-output based system is interactive and second it may suffer from double counting incidents as a process may be instigated in both the IO and LCI data. Integrated hybrid LCA overcomes those aforementioned pitfalls but only at a price of high labor and data intensity. This work aims to elaborate a new hybridisation method that avoids previously mentioned drawbacks. This technique is designed to not operate anymore at the matrix level as is the case for current hybridisation techniques but at the structural path level, per se the finest level of detail possible for the disaggregation of the Leontief inverse, and as such an ad hoc basis to carry out an hybrid analysis. It is argued that the method presented here constitutes a culmination amongst hybridization techniques. Its operability and capabilities are demonstrated before an interpretation from an input-output vantage point is carried out on a case-study not to be found in the literature, a comparison across the faculties of a university.

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.

In this study a Multi Regional Input Output model has been developed for the base year 2000, and thereafter extended and hybridized to enable a study of offshore wind power generation in Scandinavia. Foremost the per-unit environmental impact of offshore wind power generation was calculated to an average of 16.5 grams of CO2-eq. per kWh. The MRIO model offers a broad system boundary, covering a complete set of background flows and enables in this way a thorough study of the inter-regional value chains and the corresponding emissions embodied in trade. Scenarios from 2000 to 2030 for future offshore wind power were developed on the basis of GDP projections and projections for future energy demand. One baseline scenario, assuming no further offshore wind power installation, was developed, together with a Medium and a High scenario of future offshore wind power installation. The installed wind power was assumed to replace non-renewable energy sources, primarily domestically and secondly in power importing countries. The Medium and High scenario resulted in a cumulative reduction of 220 Mtons CO2-equivalents and 308 Mtons by 2030, respectively. The Norwegian offshore wind power was by a large exported, while Denmark and Sweden experienced a substantial wind power implementation into their economies, resulting in considerable increase in the percentage share of renewable energy in their electricity mix. This shows that offshore wind power could have a vital role in reaching the European Union’s target of a 20% share of renewable energy by 2020, under the assumption that a substantial capacity of wind power is installed. The results from this study provide important guidance and a broad overview of the effect a large wind power implementation will have on the Scandinavian economy.

The environmental impact of a final product can be regarded as the sum of the impacts of all processes needed to obtain it. The impacts of these processes in all individual layers of production can be quantified using contribution analysis methods. SPA is an advanced method used to identify the chain of production processes linking the most highly emitting process with the final product. This analysis was performed in Matlab, using a specialized algorithm developed by Peters and Hertwich in 1996. In this thesis we test an interdisciplinary approach combining LCA and operational research methods for doing a SPA. A mixed integer program was developed and implemented in Gams. The performance of this generalized algorithm was benchmarked against the specialized algorithm for three test cases performed on three databases of increasing complexity. The results suggest the advantage of this algorithm in performing analysis on sparse data systems compared with the classic method involving Matlab. However, Matlab’s specialized algorithm performs better for dense data systems. Many of the requirements and limitations imposed by the software involved in different steps have proved manageable. This study proves that mathematical programming can be a very useful tool for contribution analysis in general and SPA in particular.

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.