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  • 1.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kinetic Energy Storage and Magnetic Bearings, for vehicular applications2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    One of the main challenges in order to make electric cars competitive with gaspowered cars is in the improvement of the electric power system. Although many of the energy sources currently used in electric vehicles have sufficiently high specific energy, their applicability is limited due to low specific power. It would therefore be advantageous to create a driveline with the main energy storage separated from a smaller energy buffer, designed to have high power capabilities and to withstand frequent and deep discharge cycles. It has been found that rotating kinetic energy storage in flywheels is very well suited for this type of application. The work presented in this thesis and the included papers span a number of topcis Introductory overview - This section explains the concept of the modern flywheel, and investigates some of its properties. It illustrates the concepts with a number of examples, relevant for the usage of flywheels in vehicular applications. Experimental set-up - The construction of a complete electric driveline is ongoing within the division for Electricity at Uppsala University. An optimized electric machine has been constructed and connected with a programmable load, as well as with a DC power source through power electronics controlled by PWM. As a part of this system, an experimental set-up of an active magnetic bearing for two degrees-of-freedom has been constructed. The work with this device is described in detail and some preliminary results are presented. Self-bearing machine - The electric machine developed for the existing driveline is coreless, double wound and with a double rotor. In order to achieve magnetic bearing functionality in this device for all DOF, a novel Lorentz force self-bearing machine is suggested. The design is analyzed analytically and numerically.

  • 2.
    Ahmad, Noor Azlinda
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Broadband and HF radiation from cloud flashes and narrow bipolar pulses2010Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Remote measurement of electric field generated by lightning has played a major role in understanding the lightning phenomenon. Even though other measurements such as optical, photographic, channel base current and thunder signatures have contributed in this regards, due to practical reasons remote measurements of electric field is considered as the most useful tool in lightning research. This thesis discussed about the remotely measured radiation field component of electric field generated by cloud flashes (ICs) and narrow bipolar pulses (NBPs). The associated HF radiation of these events at 3 MHz and 30 MHz were also discussed. To understand the initiation process of these discharges, a comparative study of the initial pulse of cloud flashes with the initial pulse of cloud to ground flashes was conducted. The result suggests that both discharges might have been initiated by similar physical process inside the thunderclouds. Comparing the features of initial pulse of cloud and ground flashes with that of pulses appeared in the later stages of cloud flashes suggests that the initiation process involved in both flashes are not very much differ from the initiation of cloud flashes at the later stage. The average spectral amplitudes of electric field for first 120 ms of cloud flashes showed f-1 frequency dependence within the interval of 100 kHz to about 2 MHz and does not follow the standard f-2 decrease (or even more) at high frequency region. It was suggested that small pulses which repeatedly appeared at the later stage of cloud flashes might have contribute to enhance the spectral amplitude at higher frequencies. Electric fields generated by Narrow Bipolar Pulses (NBPs), which are considered as one of the strongest source of HF radiation were measured in Malaysia in the tropic and their features were also studied. Result shows a good agreement with previously published observations of NBPs in other geographical regions. The pulse duration of NBPs is varied within 20 – 30μs with the normalized peak amplitude is of the order of 10 V/m, averagely 2– 3 times larger than the peak amplitude of ordinary return strokes. They were observed to emit intense burst of HF radiation at 30 MHz. Thorough analyses and observation of these pulses found previously unreported sharp, fine peaks embedded at the rising and decaying edge of the electric field change of NBPs. Therefore it was suggested that these fine peaks were most probably to be responsible for the intense HF radiation at 30 MHz.

  • 3.
    Apelfröjd, Senad
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Electrical System for a Variable Speed Vertical Axis Wind Turbine2013Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The wind has been used as a source of energy for a long time. Wind power in power production has had a upswing in the last decade due to its renewable and clean nature. This thesis contributes to the wind power research done at the division of Electricity at Uppsala University. The research is aimed towards increasing the understanding of vertical axis wind turbines. The thesis focuses on vertical axis wind turbines of the H-rotor type with a directly driven permanent magnet synchronous generator. In this thesis a full-scale variable speed electrical grid connection system is developed and evaluated for a 12 kW prototype turbine. The proposed electrical system consists of a diode rectifier, IGBT inverter, LCL-filter and tap transformer. The full variable speed operation is achieved by adjusting transformer taps and adjusting the modulation of the inverter. The system has been assembled in a lab environment where efficiency and harmonic content have been evaluated for the operational scheme and site specifics of the 12 kW turbine. The work also looks into transformer magnetization losses, permanent magnet generator air cooling and control system design for a similar system. The results from simulations and experiments show that the tap transformer system has a high efficiency at nominal power and that the system efficiency at nominal power is increased by going up in tap. The study also shows that the total demand distortion for the system is well below 5% for full operating range of the 12 kW turbine.

    Keywords: VAWT, H-rotor, tap transformer, stall control, renewable energy, variable speed operation, transformer magnetization losses

  • 4.
    Arévalo Gonzalez, Liliana
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Numerical simulations of long spark gaps – lightning attachment and its application2010Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The Licenciate Thesis presented here is a research work on numerical simulations of two different electrical phenomena: Long gap discharges under switching impulses and the lightning attachment process of positive upward leaders. The development of a positive upward leader and the process of progress of a discharge in long gaps are composed of two intertwined physical phenomena, namely the leader channel and the corona zone. The physical description and the proposed calculations of above mentioned phenomena are based on experimental tests on long gaps. In the methodology proposed here, a geometrical approximation for the representation of the corona zone is used. Furthermore, two different approaches are applied and compared to represent the leader channel. The used methodologies for the computation of the leader channel are an engineering approximation and a physics equation that takes into account the thermoequilibrium process. In order to introduce a more realistic behavior of the discharge, statistical delays for the inception and for the tortuous characteristic of the channel were brought in. A comparison between a model with or without tortuous channel was implemented. A very good agreement was found between the physical model and the test laboratory results. In addition, based on previous works related to the physics of lightning and the lightning attachment process, a new methodology is developed and tested here. The new approach refines previous calculations; the background electric field and the ionized region considered for the advance of the leader segment are computed within an alternative approach. The proposed methodology was employed to test two engineering methods that are accepted international standards, the mesh method and the electro – geometrical method. The results demonstrated that the engineering approximations are consistent with the physical approach. Besides the electrical phenomena mentioned above, one should keep in mind that there are real effects of the lightning attachment process that are not included or are avoided to simplify the calculation. In fact, when a structure is subjected to a strong electric field, it is possible to generate multiple upward leaders from the structure. This effect has not been taken into account in the different numerical models available until now. The published models consider every upward leader as an individual case. And therefore; a first approximation to the process of generation of multiple upward leaders incepted over a structure is presented here. The preliminary results have shown that it is possible to observe an influence on the background electric field when one leader develops simultaneously with other leaders.

  • 5.
    Baudoin, Antoine
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Thermal Study of a Submerged Substation for Wave Power2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    At the Division of Electricity of Uppsala University, a wave power concept is being developed.It relies on wave energy converters, one buoy and one linear generator placed on the seabed, connected together to a submerged substation. The mechanical design is kept as simple as possible to ensure reliability. The submerged substation includes power electronics and different types of electric components. High reliability requirements on such subsea devices make thermal management a keyaspect in the design. Besides, no fans are used and the cooling strategy is fully-passive. The overall approach for thermal modelling of the substation is based on a thermal network atthe system level, and both analytic- and CFD- modelling at the component level. This work is focusing on the second prototype of substation developed at Uppsala University. In this thesis, this overall strategy is presented as well as a comprehensive temperature study for the inverterinstalled in the substation.In the present configuration, the inverters are limited to about 35 kW. The seawater temperature,the choice of material for the heat-sink, and the spacing of the component, were identified tohave an influence on this value. The importance of a good thermal contact between the heat-sink and the hull was also illustrated.

  • 6.
    Becerra, Marley
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    On The Initiation of Upward Positive Leader Discharges During Lightning Strikes2007Licentiate thesis, monograph (Other scientific)
  • 7.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Electrical System of a Wave Power Plant2009Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Wave energy is a renewable energy source with a large potential to contribute to the world's electricity production. There exist several techniques to convert the energy in the ocean waves into electric energy. The wave energy converter presented in this thesis is based on a linear synchronous generator. The generator is placed on the seabed and driven by a point absorbing buoy on the ocean surface. Instead of having one large unit, several smaller units are interconnected to increase the total installed power. By keeping the generator as simple as possible and minimizing the number of mechanical parts, the lifetime of the generator is believed to increase. To convert and interconnect the power from the generators, marine substations are used. The marine substation will be placed on the seabed and it will convert the AC with variable amplitude and variable frequency from the generators into an AC suitable for grid connection. The work presented in the thesis focuses on the first steps in the conversion, the rectification and filtering. The purpose with the study was to investigate how the generator will operate when it is connected to a non-linear load and to obtain guidelines on how larger systems could be designed. Another aim with the experiment was to see to which extent the voltage and power out from the generator can be smoothened. Offshore experiments and simulations have been done on a full scale generator connected to a diode rectifier and filter. The results show that a smooth DC output voltage after the rectifier has small ripple content. The kind of load and value of load will have an impact on the generators ability to absorb and produce power. The highest amount of absorbed power is achieved at the highest damping of the system. However, the highest damping function does not necessarily coincide with the maximum produced power. In connection to the installation of two new wave energy converters on the Swedish west coast, a marine substation will be launched at the site. Laboratory tests have been done on the marine substation and it worked as expected and the experimental data had a good agreement with the simulated data.

  • 8.
    Bülow, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Extreme Load Conditions for Wind Powered Direct Drive PM Generators2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Wind energy is a rapidly growing energy source with vast potential. Vertical axis wind turbines could be more cost-effective than the three bladed horizontal axis turbines that dominate today. A concept based on the straight bladed Darrieus turbine together with a PMgenerator operating in direct drive is studied at Uppsala University; this thesis is a part of that project. This thesis contains a study of stator core loss at low electrical frequencies. The purpose of the study was to test the reliability of core loss simulations where the specific loss at low frequency is extrapolated using specific loss at 50Hz. The simulated loss was compared to the measured loss. Passive rectifiers can be used to connect all wind energy converters in a wind farm to a mutual DC load. This principle has been demonstrated using two PM generators with very different properties. This thesis also contains two studies of a full vertical axis wind turbine prototype. The first study concerns the power coefficient of the turbine. The power coefficient was measured at several wind speeds and turbine rotational speeds. The power coefficient attains its maximum value of 29% when the tip speed ratio is 3.3. In a second study, the armature currents of the generator were used to map the harmonic content of the turbine torque. The third harmonic of the turbine torque was found to be the strongest harmonic. This thesis also presents a wind energy converter that has been tailored for a telecom tower. Several aspects of the design are unique.

  • 9.
    Carpman, Nicole
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Marine Current Resource Assessment: Measurements and Characterization2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The increasing interest in converting energy from renewable resources into electricity has led to an increase in research covering the field of marine current energy, mainly concerning tidal currents and in-stream tidal turbines. Tides have the advantage of being predictable decades ahead. However, the tidal resource is intermittent and experiences local variations that affect the power output from a conversion system. The variability is mainly due to four aspects: the tidal regime, the tidal cycle, bathymetry at the site and weather effects. Each potential site is unique, the velocity flow field at tidal sites is highly influenced by local bathymetry and turbulence. Hence, characterizing the resource requires careful investigations and providing high quality velocity data from measurement surveys is of great importance. In this thesis, measurements of flow velocities have been performed at three kinds of sites.

    A tidal site has been investigated for its resource potential in one of all of the numerous fjords in Norway. Measurements have been performed to map the spatial and temporal variability of the resource. Results show that currents in the order of 2 m/s are present in the center of the channel. Furthermore, the flow is highly bi-directional between ebb and flood flows. The site thus have potential for in-stream energy conversion. A model is proposed that predicts peak current speed from information on tidal range at the site. A corresponding model can be set up and implemented at other similar sites affected by tides, i.e. fjord inlets connecting the ocean to a fjord or a basin.

    A river site serves as an experimental site for a marine current energy converter that has been designed at Uppsala University and deployed in Dalälven, Söderfors. The flow rate at the site is regulated by an upstream hydrokinetic power plant nearby, making the site suitable for experiments on the performance of the vertical axis turbine in its natural environment. The turbine has been run in uniform flow and measurements have been performed to characterize the extent of the wake.

    An ocean current site was a target of investigation for its potential for providing utilizable renewable energy. A measurement campaign was conducted, mapping the flow both spatially and temporally. However, the site was shown to not be suitable for energy conversion using present technique.

    List of papers
    1. Measurements of tidal current velocities in the Folda fjord, Norway, with the use of a vessel mounted ADCP
    Open this publication in new window or tab >>Measurements of tidal current velocities in the Folda fjord, Norway, with the use of a vessel mounted ADCP
    2014 (English)In: 33Rd International Conference On Ocean, Offshore And Arctic Engineering, 2014, Vol 8A: Ocean Engineering, 2014Conference paper, Oral presentation only (Refereed)
    Abstract [en]

    Measurements of tidal current water velocities is an important first step in evaluating the potential for a tidal site to be used as a renewable energy resource. For this reason, on site measurements are performed at the inlet of a fjord situated at the coast of Norway. The site has an average width of 580 m and adepth of 10-15 m which is narrow and shallow enough to give rise to water velocities that can be of use for energy conversion. With the use of an Acoustic Doppler Current Profiler (ADCP) cross-section measurements are conducted along four transects. The measurements covered flood and ebb currents around one tide and the data give a first approximation of the magnitude and distribution of the flow field. Depth averaged mean current velocities are calculated along the transects for horizontal bins with sizes in the order of 50 x 50 m. Maximum mean velocity for the flood currents were 1.31 m/s and 1.46 m/s for the ebb currents. The measurements show that even a small amount of data can give an indication of the potential and characteristics ofthe site.

    Keywords
    Acoustic Doppler Current Profiler (ADCP), tidal energy resource
    National Category
    Marine Engineering Ocean and River Engineering Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-230659 (URN)000363498500053 ()978-0-7918-4550-9 (ISBN)
    Conference
    33rd International Conference on Ocean, Offshore and Arctic Engineering (OMAE2014), San Francisco, California, USA, June 8-13, 2014
    Available from: 2014-08-27 Created: 2014-08-27 Last updated: 2017-04-04Bibliographically approved
    2. Tidal resource characterization in the Folda Fjord, Norway
    Open this publication in new window or tab >>Tidal resource characterization in the Folda Fjord, Norway
    2016 (English)In: International Journal of Marine Energy, ISSN 2214-1669, Vol. 13, p. 27-44Article in journal (Refereed) Published
    Abstract [en]

    For tidal-stream energy industry to be fully realized, lower velocity sites and fjords should be developed. Finding new prospective sites for in-stream energy extraction from tidal currents is an area of ongoing research. In this paper, the tidal flow at a fjord inlet has been characterized using acoustic Doppler current profiler (ADCP) measurements. This work is based on two survey measurement techniques: transect measurements to map the spatial variability, and seabed measurements to map the temporal variability. The data was analyzed in terms of characterizing metrics, to ensure they are comparable with other resource assessments. Results show that currents exceed 1 m/s for 38% of the time with peak currents of 2.06 m/s at hub height (middle of the water column) and the directional asymmetry is less than 1° between ebb and flood, indicating a truly bi-directional flow. A simple prediction model is proposed which allows peak current speeds to be accurately predicted in the channel center from tidal range data using a linear relationship. The relationship is shown to be strong, with a correlation coefficient of 0.98 at hub height, and a standard variation typically less than 10 cm/s. Furthermore, it is show that a minimum of 9 days of measurements are required to set up the model, although it takes 29 days to reduce the error in peak speed to less than 1%. However, the error is expected to vary depending on where in the monthly tidal cycle the survey begins, it is thus recommended to measure around spring tide if the measurement period is short.

    Keywords
    Tidal resource assessment, ADCP, Characterizing metrics
    National Category
    Engineering and Technology Ocean and River Engineering Oceanography, Hydrology and Water Resources
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-266674 (URN)10.1016/j.ijome.2016.01.001 (DOI)000381687600003 ()
    Funder
    StandUpCarl Tryggers foundation
    Available from: 2015-11-10 Created: 2015-11-10 Last updated: 2018-01-10Bibliographically approved
    3. The Söderfors Project: Experimental Hydrokinetic Power Station Deployment and First Results
    Open this publication in new window or tab >>The Söderfors Project: Experimental Hydrokinetic Power Station Deployment and First Results
    Show others...
    2013 (English)Conference paper, Published paper (Refereed)
    Abstract [en]

    The Division of Electricity at Uppsala University recently deployed an experimental hydrokinetic power station for in-stream experiments at a site in a river. This paper briefly describes the deployment process and reports some initial results from measurements made at the test site.

    Keywords
    Marine Current Power, Renewable energy, Söderfors, Strömkraft, Förnybar energi, Söderfors
    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-209220 (URN)
    Conference
    10th European Wave and Tidal Energy Conference (EWTEC), 2-5 september, 2013, Aalborg, Denmark
    Projects
    Marine Current Power
    Funder
    StandUpSwedish Research Council, 621-2009-4946
    Available from: 2013-10-15 Created: 2013-10-15 Last updated: 2019-01-22Bibliographically approved
    4. Studying the Wake of a Marine Current Turbine Using an Acoustic Doppler Current Profiler
    Open this publication in new window or tab >>Studying the Wake of a Marine Current Turbine Using an Acoustic Doppler Current Profiler
    2015 (English)Conference paper, Published paper (Refereed)
    Abstract [en]

    Wake characteristics of marine current turbines are of significant importance to the development of the marine current power source. Turbine wake recovery determines spacing of turbines in arrays, and environmental impact on e.g. the seabed is heavily influenced by wake behaviour. The majority of previous studies on wakes has been performed on flow-aligned (horizontal) axis turbines and mainly carried out as scale model experiments or numerical simulations.

    This paper describes the performance of wake measurements at the Söderfors test site, where an experimental marine current power station is operated in a river. The turbine is of the cross-flow (vertical) axis type, and the measurements are performed using an Acoustic Doppler Current Profiler (ADCP) towed on the surface by a boat. Positioning data is taken from a high-accuracy Global Navigation Satellite System. The paper discusses various aspects of the methodology employed and provides examples of taken measurements.

    National Category
    Energy Engineering Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-265358 (URN)
    Conference
    11th European Wave and Tidal Energy Conference, EWTEC15, 6-11 September 2015, Nantes, France
    Available from: 2015-10-27 Created: 2015-10-27 Last updated: 2017-04-04Bibliographically approved
    5. Variability Assessment and Forecasting of Renewables: A Review for Solar, Wind, Wave and Tidal Resources
    Open this publication in new window or tab >>Variability Assessment and Forecasting of Renewables: A Review for Solar, Wind, Wave and Tidal Resources
    Show others...
    2015 (English)In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 44, p. 356-375Article in journal (Refereed) Published
    National Category
    Energy Engineering Engineering and Technology
    Research subject
    Engineering Science with specialization in Science of Electricity; Engineering Science with specialization in Solid State Physics
    Identifiers
    urn:nbn:se:uu:diva-225870 (URN)10.1016/j.rser.2014.12.019 (DOI)000351324300025 ()
    Available from: 2014-06-09 Created: 2014-06-09 Last updated: 2018-08-01
  • 10.
    de Santiago Ochoa, Juan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    AFPM Motor/Generator Flywheel for Electric Power Stabilization2009Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The study of a motor/generator for flywheel energy storage, meant to smooth the power transients in a vehicular power train, is expounded in this licentiate thesis. The proposed motor/generator has two sets of windings in the stator, rated at different power and voltage levels, and a significant moment of inertia to store energy in the form of rotational kinetic energy.

    The need of a machine with such specific requirements is described in Section 1. The power drive presented has components operated at two different voltage levels and requires certain kinetic energy storage capability to smooth the operation under transients in power. The key component that linked both voltage levels in the same driveline and smoothes the operation is a flywheel energy storage system operated simultaneously by two sets of windings.

    Flywheel energy storage systems are operated at high rotational speed to obtain high energy density. The losses in electrical machines increase rapidly with the rotational speed and unconventional solutions are required to achieve high efficiency performances. Main loss mechanisms are described in Section 2. The geometry selected for the motor/generator, in the described specific application, is the Axial-Flux, Permanent-Magnet coreless topology due to the potentially high efficiency and scalability.

    Machines with two windings in the stator with different voltage and power rates but mutual induction coupling are not described in literature. Section 3 presents an equivalent circuit and the equations that describe the electric properties of the motor/generator studied.

    Section 4 presents the analysis of an electrical machine. The dispersion of the magnetic flux in coreless machines advises against the accuracy of 2-D FEM methods. Therefore a 3-D FEM method has been developed specifically for coreless machines. The mechanical analysis of the machine rotor is also presented. The mechanical limitations of high speed machines impose also power rate restrictions due to the lack of space in the stator. A study to determine the power limits in high speed coreless machines is also presented.

    The calculation method and the loss mechanism models presented have been validated in small scale prototypes. The tests performed are presented in Section 5. A scale prototype of a machine with two voltage levels in the stator has been tested as part of a full system. The low voltage side has been driven by a low voltage DC/AC power converter while the voltage induced in the high voltage side has been rectified and connected to a variable resistance load. The results show a steady deliver of energy from the low voltage side and abrupt power transients in the power delivered in the high voltage side, showing a promising response of this novel power drive system.

  • 11.
    Ekergård, Boel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Electromagnetic Energy Converters - Rotating Motors and Linear Generators2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This licentiate thesis presents a study of the electromagnetic properties of linear synchronous permanent magnet generators, utilized in wave energy converters, and a two pole permanent magnet motor for an electrical vehicle. Both machine topologies are presented, designed with a numerical simulation tool, based on a model derived from Maxwell’s equations. Full scale prototypes of both the machines are under construction. A continued study about the impact on the magnetic circuit caused by the longitudinal ends of a linear generator is performed. The results present significant core losses in the translator and an increased cogging force caused by the longitudinal ends. Further, a new electric conversion circuit based on the electric resonance phenomena is presented. Experimental results indicate that a successful electric resonance between the generator and external circuit has been achieved. Finally, detailed analytical and numerical methods are utilized to investigate the losses in the two pole permanent magnet motor over a wide frequency interval. The results indicate that the efficiency of electrical motors in electrical vehicle system can be increased relative existing designs and argue for limiting of the gearbox. The system total efficiency and mechanical stability can thereby be increased. The work concerning the wave energy converter is a part of a larger project, the so called Lysekil Wave Power Project, whereas the work concerning the electric motor so far has been carried out as an individual project. However, a future goal is to integrate the research on the electric motor for electrical vehicle with closely related ongoing research regarding a flywheel based electric driveline for an All Electric Propulsion System.

  • 12.
    Eklund, Petter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rare Earth Metal–Free Permanent Magnet Generators2016Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Permanent magnet (PM) synchronous generators (SGs) are used in renewable energy production. The preferred PM material is neodymium-iron-boron (NdFeB), which has very high performance and, until recently, low cost. In recent years there has emerged a cost and supply insecurity in NdFeB PMs due to export restrictions imposed by China, where the majority of the raw materials are produced. In this thesis various methods of avoiding the use of PM materials based on NdFeB, or other rare earth metals, are investigated.

    One approach is the use of the cheap and abundant ferrite PM. A ferrite PM rotor intended to be interchangeable with an NdFeB PM rotor is designed and built. Some initial investigation of the performance of the new rotor, and how this relates to manufacturing tolerances, is also made.

    Another approach is to make parameter studies in anticipation of new PM materials. A study of how three different rotor topologies perform with different PM materials, described by their remanence and recoil permeability, is made. The rotor topologies are: a spoke type PM rotor, a surface mounted PM rotor and a capped PM rotor.

    It is concluded that a viable replacement rotor can be designed using ferrite PMs. The new rotor will be heavier and mechanically more complex, and give slightly lower output voltage. Losses in the machine will increase slightly. A study is made on the impact of manufacturing tolerances on the performance of the resulting rotor.

    The different rotor topologies work best with different PM material properties. The surface mounted PM and capped PM rotors require higher remanence for good performance; the spoke type PM rotor works well with larger amounts of low remanence material. The recoil permeability should be low for the surface mounted and high for the capped PM rotor.

    List of papers
    1. A Complete Design of a Rare Earth Metal-Free Permanent Magnet Generator
    Open this publication in new window or tab >>A Complete Design of a Rare Earth Metal-Free Permanent Magnet Generator
    2014 (English)In: Machines, ISSN 2075-1702Article in journal (Refereed) Published
    Abstract [en]

    The price of rare-earth metals used in neodymium-iron-boron (NdFeB) permanent magnets (PMs) has fluctuated greatly recently. Replacing the NdFeB PMs with more abundant ferrite PMs will avoid the cost insecurity and insecurity of supply. Ferrite PMs have lower performance than NdFeB PMs and for similar performance more PM material has to be used, requiring more support structure. Flux concentration is also necessary, for example, by a spoke-type rotor. In this paper the rotor of a 12 kW NdFeB PM generator was redesigned to use ferrite PMs, reusing the existing stator and experimental setup. Finite element simulations were used to calculate both electromagnetic and mechanical properties of the design. Focus was on mechanical design and feasibility of construction. The result was a design of a ferrite PM rotor to be used with the old stator with some small changes to the generator support structure. The new generator has the same output power at a slightly lower voltage level. It was concluded that it is possible to use the same stator with either a NdFeB PM rotor or a ferrite PM rotor. A ferrite PM generator might require a larger diameter than a NdFeB generator to generate the same voltage.

    Place, publisher, year, edition, pages
    Basel, Switzerland: Multidisciplinary Digital Publishing Institute, 2014
    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-236639 (URN)10.3390/machines2020120 (DOI)
    Available from: 2014-11-20 Created: 2014-11-20 Last updated: 2018-11-22
    2. Air Gap Magnetic Flux Density Variations due to Manufacturing Tolerances in a Permanent Magnet Synchronous Generator
    Open this publication in new window or tab >>Air Gap Magnetic Flux Density Variations due to Manufacturing Tolerances in a Permanent Magnet Synchronous Generator
    2016 (English)In: 2016 XXII INTERNATIONAL CONFERENCE ON ELECTRICAL MACHINES (ICEM), IEEE, 2016, p. 93-99Conference paper, Published paper (Refereed)
    Abstract [en]

    The impact of manufacturing tolerances on the performance of a permanent magnet synchronous generator is investigated. A generator with a flux concentrating spoke-type rotor, with ferrite permanent magnets, is used in the investigation. Measurements of the air gap magnetic flux density, the air gap length, as well as the magnetization and size of the permanent magnets have been performed. Correlations are calculated and causalities are discussed. It is found that the permanent magnets used are below tolerance in remanent magnetic flux density, that the air gap length is smaller than specified, and that the resulting air gap magnetic flux density is lower than specified. From the results it can be concluded that the design should be made with tolerances in mind and that quality control of parts, especially of PM magnetization, is important for machine performance.

    Place, publisher, year, edition, pages
    IEEE, 2016
    National Category
    Other Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-292962 (URN)10.1109/ICELMACH.2016.7732511 (DOI)000390884900012 ()978-1-5090-2538-1 (ISBN)
    Conference
    22nd International Conference on Electrical Machines (ICEM), SEP 04-07, 2016, Lausanne, SWITZERLAND
    Funder
    Swedish Research Council, 2012-4706ÅForsk (Ångpanneföreningen's Foundation for Research and Development), 12-295
    Available from: 2016-05-16 Created: 2016-05-11 Last updated: 2018-11-22Bibliographically approved
    3. The Influence of PM Material Properties on Choice of Generator Magnetic Circuit Topology
    Open this publication in new window or tab >>The Influence of PM Material Properties on Choice of Generator Magnetic Circuit Topology
    2016 (English)Manuscript (preprint) (Other academic)
    National Category
    Other Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-292965 (URN)
    Conference
    XXII International Conference on Electrical Machines (ICEM)
    Funder
    Swedish Research Council, 2012-4706
    Available from: 2016-05-16 Created: 2016-05-11 Last updated: 2016-12-13
  • 13.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hydrodynamic Modeling of the Energy Conversion from Ocean Waves to Electricity2009Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Research within wave energy conversion has seen a large increase during the last years. Several concepts are now taking the final steps towards commercialization. Conversion from wave energy for grid connection is a multi disciplinary task involving many challenges; one being the fact that the device has to be dimensioned for a nominal power and still be able to withstand the extreme powers in some of the harshest conditions on earth. The research and development of a concept based on a point absorber converting wave energy to a direct driven linear generator were initiated in 2002 at Uppsala University. Theoretical simulations have now been compared to offshore full scale experiments at the research test site. This thesis focuses on the hydrodynamic wave/device interaction for a Wave Energy Converter subjected to Swedish west coast wave climate. First conclusions on the Wave Energy Converters dynamics and energy absorption have been drawn based on earlier results. A thorough study of the sea state of Skagerrak and Kattegat has been made to asses the potential and get design parameters for the Wave Energy Converter. Based on that, a Wave Energy Converter model using potential linear wave theory and with the generator as a linear damper, has been developed to simulate the dynamics and power capture ratio. The model has also been used to simulate how biomass accumulated on the buoy will affect the dynamics. As a next step, the model has been further developed to simulate a two component system having optimum amplitude response at frequencies coinciding with Swedish west coast conditions. Results are presented for time series of real ocean wave data collected at the research test site as well as for empirical spectra. An enhanced amplitude response for the two component system is achieved by adding supplementary inertia by use of the added mass from a submerged body. Simulations show that the increased velocity in the two component system gives an increased power capture ratio by a factor of two compared to the regular system of a point absorber. The increased velocity also leads to a decrease in optimal damping for energy absorption with 60 %. The main weakness of the hydrodynamical modeling is thought to be the neglected viscosity that might lead to unpredicted energy losses, pointing out the direction for improvement and future work.

  • 14.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Improving the functionality of synchronous machines using power electronics2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    With the advent of modern power electronics there is reason to explore what can be achieved when it is applied to a mature technology like synchronous machines. In this text several concepts will be presented on how it is possible to control forces and how to get better performance out of synchronous machines by using power electronics. Methodologies to create radial forces by controlling the field current in a standard series connected rotor winding as well as when the winding is split in to several segments is presented. By segmenting the rotor a resulting force vector can be created to cancel forces due to unbalanced magnetic pull.

    It is also shown that inverting the field current with respect to the stator field enables line start of synchronous machines without using damper bars, frequency converters, or starting motors.

    Some first results from the installation and testing of an electromagnetic thrust bearing installed in unit U9 in the hydropower station in Porjus are presented. The benefits of the system is increased reliability and higher efficiency of the thrust bearing system.

    An evaluation of a 2-stage brushless excitation system was done, different rotating power electronics topologies were tested in the stationary frame connected to a six-phase permanent magnet brushless exciter. The rotating control and measurement system for the power electronics is presented. Potential benefits of the system is that there is no need for brushes to transfer the field current to the rotor winding, fast response time due to actively controlled electronics, independence of the station bus voltage, and reduced maintenance.

    List of papers
    1. Altering Flux Density Harmonics in the Air-gap of Synchronous Machines by Active Control of the Field Current
    Open this publication in new window or tab >>Altering Flux Density Harmonics in the Air-gap of Synchronous Machines by Active Control of the Field Current
    (English)In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948Article in journal (Refereed) Accepted
    Abstract [en]

    Flux density harmonics in the air-gap of electrical machines create distorted voltage waveforms and can induce vibrations. These problems are difficult to mitigate when the machine is already in operation and therefore a lot of effort is made during the design phase to eliminate them. Still, many in-operation machines experience problems related to harmonics and often the solution is to mechanically reinforce and change modal shapes which is expensive and inconvenient. Using a current controlled switched power supply to excite a synchronous machine and adding specific harmonics to the DC-field current it is shown that it is possible to alter the harmonic content of the flux density in the air-gap, and thus affect  voltage harmonics and the exciting magnetic forces. The method is verified and compared with simulations and experiments on an existing electrical machine. 

    Keywords
    Air-gap flux density, Finite element, Harmonic waves, Noise reduction, Power electronics, Synchronous machines
    National Category
    Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-333565 (URN)
    Available from: 2017-11-15 Created: 2017-11-15 Last updated: 2017-11-20
    2. Demonstration of synchronous motor start by rotor polarity inversion
    Open this publication in new window or tab >>Demonstration of synchronous motor start by rotor polarity inversion
    2017 (English)In: Article in journal (Refereed) Submitted
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-328081 (URN)
    Available from: 2017-08-16 Created: 2017-08-16 Last updated: 2017-11-20
    3. Magnetic thrust bearing for a hydropower unit with a Kaplan turbine
    Open this publication in new window or tab >>Magnetic thrust bearing for a hydropower unit with a Kaplan turbine
    2017 (English)Manuscript (preprint) (Other academic)
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-328082 (URN)
    Available from: 2017-08-16 Created: 2017-08-16 Last updated: 2017-11-20
    4. Design and Characterization of a Rotating Brushless Outer Pole PM Exciter for a Synchronous Generator
    Open this publication in new window or tab >>Design and Characterization of a Rotating Brushless Outer Pole PM Exciter for a Synchronous Generator
    Show others...
    2017 (English)In: IEEE transactions on industry applications, ISSN 0093-9994, E-ISSN 1939-9367, Vol. 53, no 3, p. 2016-2027Article in journal (Refereed) Published
    Abstract [en]

    Generally, PM machines are used as PMG pre-exciters in 3-stage brushless excitations systems. This paperpresents the design, characterization and prototyping of a rotatingbrushless PM exciter used in a proposed 2-stage excitation systemfor a synchronous generator. The proposed design reduces thenumber of components compared with conventional systems.A comparison with the state-of-the-art conventional excitationsystems is given. The design of a fast-response, or high initialresponse, brushless exciter requires active rectification on therotating frame, replacing the non-controllable diode bridge. Theobjective was to construct an exciter with the capability of a50 Aoutput field current as well as a high value of the available ceilingvoltage and ceiling current. The final exciter was constructed to befitted into an in-house synchronous generator test setup. A finiteelement model of the exciter was validated with experimentalmeasurements. The exciter prototype is also compared with analternative armature design with non-overlapping single-layerconcentrated windings but with the same main dimensions.The paper includes a general design procedure suitable foroptimization of PM brushless exciters that fulfill the requirementsof their synchronous generators and the grid.

    National Category
    Other Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-315594 (URN)10.1109/TIA.2017.2669890 (DOI)000402062600031 ()
    Available from: 2017-02-15 Created: 2017-02-15 Last updated: 2018-09-17Bibliographically approved
    5. Comparison of Thyristor Rectifier Configurations for a Six-Phase Rotating Brushless Outer Pole PM Exciter
    Open this publication in new window or tab >>Comparison of Thyristor Rectifier Configurations for a Six-Phase Rotating Brushless Outer Pole PM Exciter
    Show others...
    2018 (English)In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 65, no 2, p. 968-976Article in journal (Refereed) Published
    Abstract [en]

    Recent technological developments have caused a renewed interest in the brushless excitation system. With the application of wireless communication, the conventional diode bridge has been replaced with fully controllable thyristors on the shaft. It offers the same dynamic performance as the conventional static excitation system. The thyristor bridge of the conventional three-phase exciter needs to be controlled with a high firing angle in normal operation in order to fulfill a requirement of both a high ceiling voltage and a high ceiling current. A high firing angle causes high torque ripple to be absorbed by the exciter stator and a low power factor results in a low utilization of the designed exciter. In this contribution, we present a strategy that solves this problem by looking into combinations of thyristor configurations of a double-star six-phase connection of the exciter. Experimental results are used to verify the circuit models implemented for this investigation. A hybrid-mode 12-pulse thyristor bridge configuration seems to be a good solution for implementations in commercial apparatus. An additional switch interconnects two separate thyristor bridges from parallel- to series connection at the rectifier output, and utilizes the advantages of both topologies.

    Keywords
    Bridge circuits, Generators, Shafts, Thyristors, Topology, Torque, Windings, 12-pulse thyristor rectifiers, Fast-response exciters, active rectification, brushless exciters, hybrid-mode operation, multiphase machines, outer-pole PM machines, rotating exciters, synchronous generators
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-328391 (URN)10.1109/TIE.2017.2726963 (DOI)000418415200002 ()
    Available from: 2017-08-22 Created: 2017-08-22 Last updated: 2018-01-25Bibliographically approved
    6. Testing of Active Rectification Topologies on a Six-Phase Rotating Brushless Outer Pole PM Exciter
    Open this publication in new window or tab >>Testing of Active Rectification Topologies on a Six-Phase Rotating Brushless Outer Pole PM Exciter
    Show others...
    2018 (English)In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 33, no 1, p. 59-67Article in journal (Refereed) Published
    Abstract [en]

    The static exciter is dominating among large grid-connected generators due to the weak dynamic performance of conventional brushless exciters. In this paper, a six-phase outer pole permanent magnet rotating brushless exciter is evaluated with different active rectification topologies. Both thyristor-based and chopper-based topologies are considered. A fast-response brushless excitation system is obtained by replacing the conventional rotating diode bridge rectifier with the proposed active rectification topologies on the shaft. The given two-stage system generates its own excitation power directly from the shaft, contrary to static exciters. The selection of an appropriate rectification topology could minimize the rotor armature phase currents for a given generator field current. The objective is a high power factor and a high utilization of the exciter machine. An optimal rectification topology makes higher ceiling currents possible, improving the transient behavior of the synchronous generator. In this paper we show that six-phase topologies add complexity, but improve exciter redundancy, increase the available ceiling voltage and reduce the steady state torque ripple. Experimental results are given for validating the models implemented for the analysis.

    National Category
    Other Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-328396 (URN)10.1109/TEC.2017.2746559 (DOI)000425623700007 ()
    Available from: 2017-08-22 Created: 2017-08-22 Last updated: 2018-04-25Bibliographically approved
    7. Failure Modes Demonstration and Redundant Postfault Operation of Rotating Thyristor Rectifiers on Brushless Dual-Star Exciters
    Open this publication in new window or tab >>Failure Modes Demonstration and Redundant Postfault Operation of Rotating Thyristor Rectifiers on Brushless Dual-Star Exciters
    2019 (English)In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 66, no 2, p. 842-851Article in journal (Refereed) Published
    Abstract [en]

    The excitation system plays a critical role in the operation of synchronous generators. An equipment failure could impact the voltage quality for smaller grids. Further, it can lead to cost penalties and reduced production for the power plant owner. Recently, a new high-speed-response rotating brushless exciter was developed that employs remote control of the rotating thyristors on the generator shaft. This has led to new possibilities for improving the performance of brushless exciters. This contribution investigates the failure modes of a dual-star outer pole exciter that feeds two separate thyristor bridges connected in parallel during normal operation. The possibility of redundant postfault operation due to open-thyristor or open-phase faults are demonstrated using experimental testing. The system is compared with the fault performance of a conventional three-phase system. This work includes the implementation and validation of a fault-predicting double d-q exciter model. In addition, the dangerous effects of a shorted-thyristor fault are investigated. A "skip firing" protection technique is briefly demonstrated for the fast isolation of such faults, yielding nondestructive postfault recovery and redundant failure-mode operation. The evidence shows that the dual-star exciter is a competitive choice for the future development of fault-tolerant brushless exciters.

    Keywords
    Brushless exciters, double-star windings, dual-port electrical machines, 12-pulse thyristor bridges, open-phase faults, open-thyristor faults, shorted thyristors
    National Category
    Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-333567 (URN)10.1109/TIE.2018.2833044 (DOI)
    Note

    Title in thesis list of papers (Nøland): Failure-Modes of a Thyristor-Controlled Six-Phase Rotating Brushless Outer Pole PM Exciter with 12-Pulse Hybrid-Mode Operation

    Available from: 2017-11-15 Created: 2017-11-15 Last updated: 2019-12-09Bibliographically approved
    8. Design and characterization of a rotating brushless PM exciter for a synchronous generator test setup
    Open this publication in new window or tab >>Design and characterization of a rotating brushless PM exciter for a synchronous generator test setup
    Show others...
    2016 (English)In: Design and characterization of a rotating brushless PM exciter for a synchronous generator test setup / [ed] IEEE Xplore, 2016, p. 259-265Conference paper, Published paper (Refereed)
    Abstract [en]

    This paper deals with the characterization and construction of a rotating brushless PM exciter intended for synchronous generator excitation purposes. Traditionally, PM exciters are used as pre-exciters in synchronous generator excitations systems. In order to reduce the number of components and to increase the step time response of the system, a PM exciter is designed as an outer pole PM machine, with permanent magnets on the stator and armature windings on the rotor. The exciter was constructed electrically and mechanically to be fitted into an in-house synchronous generator test setup. A finite element model of the exciter was validated with no-load measurements of voltages and magnetic flux densities. The exciter was then characterized with unsaturated and saturated parameters.

    Keywords
    Brushless exciters, rotating exciters, permanent magnet machines, machine design, voltage measurement
    National Category
    Other Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-292798 (URN)10.1109/ICELMACH.2016.7732536 (DOI)000390884900037 ()9781509025381 (ISBN)
    Conference
    International Conference on Electrical Machines 2016 (ICEM'16), Lausanne, SWITZERLAND, SEP 04-07, 2016
    Available from: 2016-05-09 Created: 2016-05-09 Last updated: 2017-11-20Bibliographically approved
    9. Evaluation of different power electronic interfaces for control of a rotating brushless PM exciter
    Open this publication in new window or tab >>Evaluation of different power electronic interfaces for control of a rotating brushless PM exciter
    Show others...
    2016 (English)In: Proceedings Of The IECON 2016 - 42nd Annual Conference of the IEEE Industrial Electronics Society, IEEE, 2016, p. 1924-1929Conference paper, Published paper (Refereed)
    Abstract [en]

    his paper investigates the performance of different power electronic interfaces for a rotating brushless permanent magnet exciter, designed for a synchronous generator test setup. A passive rotating diode bridge is commonly used as the rotating interface on conventional brushless excitation systems. Those systems are known to be slow dynamically, since they cannot control the generator field voltage directly. Including active switching components on the rotating shaft, like thyristors or transistors, brushless excitation systems can be comparable to static excitation systems. Brushless excitation systems has the benefit of less regular maintenance. With permanent magnets on the stator of the designed exciter, the excitation system improves its field forcing capability. Results show that modern power electronic interfaces utilize the exciter machine optimally, increase the power factor, reduce the torque pulsations, maintain the available field winding ceiling voltage and improve the field winding controllability.

    Place, publisher, year, edition, pages
    IEEE, 2016
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-328394 (URN)000399031202033 ()978-1-5090-3474-1 (ISBN)
    Conference
    42nd annual conference of the IEEE Industrial Electronics Society, Florence, October 27-27, 2016
    Available from: 2017-08-22 Created: 2017-08-22 Last updated: 2018-04-04Bibliographically approved
    10. Active Current Sharing Control Method for Rotating Thyristor Rectifiers on Brushless Dual-Star Exciters
    Open this publication in new window or tab >>Active Current Sharing Control Method for Rotating Thyristor Rectifiers on Brushless Dual-Star Exciters
    2018 (English)In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 33, no 2, p. 893-896Article in journal (Refereed) Published
    Abstract [en]

    A new high-speed-response dual-star brushless rotating exciter has been recently proposed, which utilizes two rotating thyristor rectifiers in a hybrid-mode topology. However, dissymmetries tend to occur in large-scale apparatus, which ultimately results in an undesired unbalanced loading of the topology. Moreover, the topology provides a possibility for compensation via asymmetrical firing, which serves as a promising solution to be investigated. This letter proposes an active current sharing adjustment method between the parallel thyristor bridges. The method improves controllability and performance compared with the alternative “skip firing” approach, and it can replace the interphase reactors (IPRs) in large direct current applications.

    Keywords
    AC generator excitation, asymmetrical firing, hybrid-mode 12-pulse thyristor rectifier, brushless exciters
    National Category
    Other Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-333568 (URN)10.1109/TEC.2018.2813664 (DOI)000432993800044 ()
    Available from: 2017-11-15 Created: 2017-11-15 Last updated: 2018-08-20Bibliographically approved
    11. Initial Performance Tests of a Permanent Magnet Thrust Bearing for a Hydropower Synchronous Generator Test-Rig
    Open this publication in new window or tab >>Initial Performance Tests of a Permanent Magnet Thrust Bearing for a Hydropower Synchronous Generator Test-Rig
    2016 (English)Conference paper, Oral presentation with published abstract (Refereed)
    National Category
    Electrical Engineering, Electronic Engineering, Information Engineering
    Identifiers
    urn:nbn:se:uu:diva-284944 (URN)
    External cooperation:
    Conference
    AIM 2016