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  • 1.
    Apelfröjd, Senad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bülow, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kjellin, Jon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Laboratory verification of system for grid connection of a 12 kW variable speed wind turbine with a permanent magnet synchronous generator2012In: EWEA 2012 Annual Event, Copenhagen, Denmark, 2012, 2012Conference paper (Refereed)
    Abstract [en]

    In this paper the first laboratory tests of the gridconnection system, connected to a resistiveload, for a vertical axis wind turbine (VAWT)with a permanent magnet generator arepresented. The system is based on a taptransformertopology with a voltage sourceinverter and an LCL-filter. The use of a taptransformer topology eliminates the need for aDC-DC converter to handle the variations inDC voltage. The harmonic content of thecurrents from experiments and simulationsperformed in Simulink using different taps onthe transformer are presented. The simulatedcurrents, fed to the resistive load, have a totalharmonic distortion (THD) of 0.5% to 0.9% forthe different taps. The experimental systemhas a current THD ranging from 1.8% to 2.8%.The difference is expected to be due tounbalances, delays and dead times in theexperimental set-up as the major THDcontribution is from harmonic orders below 11.The results show that an LCL filter can bedesigned to meet the demands on powerquality for grid connection of the system withall the taps of the tap transformer inaccordance with IEEE 519-1992.

  • 2.
    Apelfröjd, Senad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Evaluation of Harmonic Content from a Tap Transformer Based Grid Connection System for Wind Power2013In: Journal of Renewable Energy, Vol. 2013, p. 8-Article in journal (Refereed)
    Abstract [en]

    Simulations done in MATLAB/Simulink together with experiments conducted at the Ångströms laboratory are used to evaluate and discuss the total harmonic distortion (THD) and total demand distortion (TDD) of a tap transformer based grid connection system. The grid connection topology can be used with different turbine and generator topologies and is here applied on a vertical axis wind turbine (VAWT) with a permanent magnet synchronous generator (PMSG) and its operational scheme. The full variable-speed wind conversion system consists of a diode rectifier, DC link, IGBT inverter, LCL-filter, and tap transformer. The full variable-speed operation is enabled by the use of the different step-up ratios of the tap transformer. In the laboratory study, a full experimental setup of the system was used, a clone of the on-site PMSG driven by a motor was used, and the grid was replaced with a resistive load. With a resistive load, grid harmonics and possible unbalances are removed. The results show a TDD and THD below 5% for the full operating range and harmonic values within the limits set up by IEEE-519. Furthermore, a change in tap, going to a lower step-up ratio, results in a reduction in both THD and TDD for the same output power.

  • 3.
    Apelfröjd, Senad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    System Efficiency of a Tap Transformer Based Grid Connection Topology Applied on a Direct Driven Generator for Wind Power2014In: Scientific World Journal, E-ISSN 1537-744X, p. 784295-Article in journal (Refereed)
    Abstract [en]

    Results from experiments on a tap transformer based grid connection system for a variable speed vertical axis wind turbine are presented. The tap transformer based system topology consists of a passive diode rectifier, DC-link, IGBT inverter, LCL-filter, and tap transformer. Full range variable speed operation is enabled by using the different step-up ratios of a tap transformer. Simulations using MATLAB/Simulink have been performed in order to study the behavior of the system. A full experimental set up of the system has been used in the laboratory study, where a clone of the on-site generator was driven by an induction motor and the system was connected to a resistive load to better evaluate the performance. Furthermore, the system is run and evaluated for realistic wind speeds and variable speed operation. For a more complete picture of the system performance, a case study using real site Weibull parameters is done, comparing different tap selection options. The results show high system efficiency at nominal power and an increase in overall power output for full tap operation in comparison with the base case, a standard transformer. In addition, the loss distribution at different wind speeds is shown, which highlights the dominant losses at low and high wind speeds. Finally, means for further increasing the overall system efficiency are proposed.

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  • 4.
    Bolund, Björn
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Segergren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Solum, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Perers, Richard
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Lundström, Ludvig
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Lindblom, Adam
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Thorburn, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Ericsson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Nilsson, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Ivanova, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Danielsson, O
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Bengtsson, H
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Sjöstedt, E
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Sundberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Karlsson, K-E
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Wolfbrandt, Ane
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Ågren, Olov
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rotating and Linear Syncronous Generators for Renewable Electric Energy Conversion: an Update of the Ongoing Research Projects at Uppsala University2004Conference paper (Other academic)
  • 5.
    Bülow, Fredrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    No-load core loss prediction of PM generator at low electrical frequency2012In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 43, p. 389-392Article in journal (Refereed)
    Abstract [en]

    A method for measurement of frequency dependent electromagnetic core loss of a permanent magnet generator is presented. Core loss of a PM generator is measured at electrical frequencies ranging from 4 to 14 Hz. Core loss in the same interval is simulated using the finite element method and frequency domain loss separation. The specific loss is both extrapolated from specific loss at 50 Hz and measured directly at 4, 8, 12 and 16 Hz. Core loss simulations based on extrapolated specific loss are 38–53% smaller than measured loss. Core loss simulations based on specific loss measured at 4, 8, 12 and 16 Hz are 19–23% smaller than measured loss.

  • 6.
    Bülow, Fredrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kjellin, Jon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bergkvist, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ström, P
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Adapting a VAWT with PM generator to telecom applications2010In: European Wind Energy Conference & Exhibition, Warsaw, Poland, 2010Conference paper (Refereed)
  • 7.
    D. Silva, Marcelo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    On the Mitigation of Leakage Flux in Spoke Type Permanent Magnet Synchronous Machines2022In: 2022 International Conference on Electrical Machines (ICEM), IEEE, 2022, p. 302-308Conference paper (Refereed)
    Abstract [en]

    The use of rare-earth elements in permanent magnets rises economic, environmental and supply-chain related concerns. Instead, ferrite magnets have been researched as an alternative. The magnetic flux concentration capacity of the Spoke Type Permanent Magnet Synchronous Motor (PMSM) and the low magnetic remanence of the ferrite magnet make them complementary strategies towards the desirable performance. However, if restricted to conventional manufacturing processes and materials, the mechanical design is a challenging step of the development of these machines. This paper explores how mechanical constraints impact electromagnetic performance. To access the interdependency of the performance and the mechanical constraints, finite element analyses are done both in the mechanical and electromagnetic domain. The results show that the mechanical constraints have an impact on the performance, although it is possible to reduce it by adapting the design to the electromagnetic and mechanical properties of the electrical steel.

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  • 8.
    de Santiago, Juan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ekergård, Boel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ferhatovic, Senad
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Electrical Motor Drivelines in Commercial All Electric Vehicles: a Review2012In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 61, no 2, p. 475-484Article in journal (Refereed)
    Abstract [en]

    This paper presents a critical review of the drivelines in all Electric Vehicles (EVs). The motor topologies that are the best candidates to be used in EVs are presented. The advantages and disadvantages of each electric motor type are discussed from a system perspective. A survey of the electric motors used in commercial EVs is presented. The survey shows that car manufacturers are very conservative when it comes to introducing new technologies. Most of the EV’s in the market mount a single induction or permanent magnet motor with a traditional mechanic driveline with a differential. The study illustrates that comparisons between the different motors are made difficult by the large number of parameters and the lack of a recommended test scheme. The authors propose that a standardized drive cycle is used to test and compare motors.

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  • 9.
    Deglaire, Paul
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kjellin, Jon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Experimental results from a 12 kW vertical axis wind turbine with a direct driven PM synchronous generator2007Conference paper (Other academic)
    Abstract [en]

    Experimental results from a three bladed vertical axis wind turbine with a direct driven PM synchronous generatorare presented. The H-rotor turbine, independent of wind direction, does not require any yaw mechanism.Furthermore, the variable speed, stall regulated turbine does not require pitch mechanism. The specifically designeddirectly driven generator eliminates the need for a gearbox. All electrical equipment, including generator, are placedon the ground. This reduces the weight that has to be supported by the structure and simplifies maintenance. Thus, theoverall strength of this concept is simplicity.The H-rotor has five meter long blades that are tapered at the tips. The aerodynamic torque is transferred to thegenerator via a 5.4 meter long drive shaft supported by a tower. A universal joint connects the drive shaft to thegenerator shaft, cancelling any transverse bending moments from the turbine on the generator. The generator acts as amotor to start up the turbine using a separate auxiliary winding. The turbine has a swept area of 30 m2 and is rated at12 kW in 12 m/s winds for 127 rpm.The turbine has been placed on a site where the wind resources have been extensively documented. The wind datarecord is more then ten years and includes data from various heights giving an accurate wind mapping of the area.The experimental aerodynamic power curve in turbulent wind conditions is presented. Considering the highlyturbulent wind conditions and the small size of the wind turbine these results are encouraging.

  • 10.
    Eklund, Petter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Air Gap Magnetic Flux Density Variations due to Manufacturing Tolerances in a Permanent Magnet Synchronous Generator2016In: 2016 XXII INTERNATIONAL CONFERENCE ON ELECTRICAL MACHINES (ICEM), IEEE, 2016, p. 93-99Conference 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.

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  • 11.
    Eklund, Petter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    The influence of permanent magnet material properties on generator rotor design2019In: Energies, E-ISSN 1996-1073, Vol. 12, no 7, article id 1314Article in journal (Refereed)
    Abstract [en]

    Due to the price and supply insecurities for rare earth metal-based permanent magnet (PM) materials, a search for new PM materials is ongoing. The properties of a new PM material are not known yet, but a span of likely parameters can be studied. This paper presents an investigation on how the remanence and recoil permeability of a PM material affect its usefulness in a low speed, multi-pole, and PM synchronous generator. Demagnetisation is also considered. The investigation is carried out by constrained optimisation of three different rotor topologies for maximum torque production for different PM material parameters and a fixed PM maximum energy. The rotor topologies used are surface mounted PM rotor, spoke type PM rotor and an interior PM rotor with radially magnetised PMs. The three different rotor topologies have their best performance for different kinds of materials. The spoke type PM rotor is the best at utilising low remanence materials as long as they are sufficiently resistant to demagnetisation. The surface mounted PM rotor works best with very demagnetisation resistant PM materials with a high remanence, while the radial interior PM rotor is preferable for high remanence materials with low demagnetisation resistance.

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  • 12.
    Eklund, Petter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    The Influence of PM Material Properties on Choice of Generator Magnetic Circuit Topology2016Manuscript (preprint) (Other academic)
  • 13.
    Eklund, Petter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Winding Design Independent Calculation Method for Short Circuit Currents in Permanent Magnet Synchronous Machines2018In: 2018 XIII International Conference on Electrical Machines (ICEM), 2018, p. 1021-1027Conference paper (Refereed)
    Abstract [en]

    When designing permanent magnet (PM) synchronous machines the demagnetizing effect of short circuit currents on the PMs needs to be considered. In some cases there can be a need to estimate the demagnetizing field from the winding without knowing the winding scheme. To do this a lumped parameter model of the dynamics of the magnetic field and armature current density distribution is proposed. Validation of the model using two different machines shows acceptable agreement. The proposed model is found to be useful for its particular purpose of determining the approximate short circuit current distribution in the armature without knowing the winding design.

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  • 14.
    Eklund, Petter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Halmstad Univ, Halmstad, Sweden.
    Sjolund, Jonathan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Berg, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Chalmers Univ Technol, Div Elect Machines & Power Elect, S-41296 Gothenburg, Sweden.
    Experimental Evaluation of a Rare Earth-Free Permanent Magnet Generator2021In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 36, no 1, p. 3-10Article in journal (Refereed)
    Abstract [en]

    Low speed, high torque machines are used in wind turbines where the turbine rotor is directly connected to the generator. A permanent magnet synchronous generator using high-energy rare-earth permanent magnets (PMs) is one common choice for this application, but rare-earth PMs have supply insecurities and cost risks. A rare-earth free PM generator, using ferrite PMs in a spoke-type rotor, for use in a 12 kW experimental wind turbine is built and tested. Voltages and currents at load and no load are measured, as well as the magnetic field in the end regions of the machine.The measurements are compared to two-dimensional finite element design calculations. Simulations of the three-dimensional magnetic field in the end regions are also made. The generator can deliver the required power at nominal speed and has low harmonic content in the output. The measured voltage is lower than expected, requiring a higher current than calculated for the rated power. Three-dimensional magnetic field simulations show that there are leakage flux paths in the end-regions that the two-dimensional design calculations overlook, explaining the discrepancy between simulations and measurements.

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  • 15.
    Eklund, Petter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Sjolund, Jonathan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Magnetic End LeakageFlux in a Spoke Type Rotor Permanent Magnet SynchronousGenerator2017Conference paper (Other academic)
    Abstract [en]

    The spoke type rotor can be used to obtain magnetic flux concentration in permanent magnet machines. This allows the air gap magnetic flux density to exceed the remanent flux density of the permanent magnets but gives problems with leakage fluxes in the magnetic circuit. The end leakage flux of one spoke type permanent magnet rotor design is studied through measurements and finite element simulations. The measurements are performed in the end regions of a 12 kW prototype generator for a vertical axis wind turbine. The simulations are made using three dimensional finite elements to calculate the magnetic field distribution in the end regions of the machine. Also two dimensional finite element simulations are performed and the impact of the two dimensional approximation is studied. It is found that the magnetic leakage flux in the end regions of the machine is equal to about 20 % of the flux in the permanent magnets. The overestimation of the performance by the two dimensional approximation is quantified and a curve-fitted expression for its behavior is suggested.

  • 16.
    Eklund, Petter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Sjökvist, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Mats, Leijon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A Complete Design of a Rare Earth Metal-Free Permanent Magnet Generator2014In: Machines, E-ISSN 2075-1702Article in journal (Refereed)
    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.

  • 17.
    Elamalayil Soman, Deepak
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Loncarski, Jelena
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Gerdin, Lisa
    Eklund, Petter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Development of Power Electronics Based Test Platform for Characterization and Testing of Magnetocaloric Materials2015In: Advances in Electrical Engineering, ISSN 2356-6655, Vol. 2015, no 670624, p. 7-Article in journal (Refereed)
    Abstract [en]

    Magnetocaloric effects of various materials are getting more and more interesting for the future, as they can significantly contribute towards improving the efficiency of many energy intensive applications such as refrigeration, heating, and air conditioning. Accurate characterization of magnetocaloric effects, exhibited by various materials, is an important process for further studies and development of the suitable magnetocaloric heating and cooling solutions. The conventional test facilities have plenty of limitations, as they focus only on the thermodynamic side and use magnetic machines with moving bed of magnetocaloric material or magnet. In this work an entirely new approach for characterization of the magnetocaloric materials is presented, with the main focus on a flexible and efficient power electronic based excitation and a completely static test platform. It can generate a periodically varying magnetic field using superposition of an ac and a dc magnetic field. The scale down prototype uses a customized single phase H-bridge inverter with essential protections and an electromagnet load as actuator. The preliminary simulation and experimental results show good agreement and support the usage of the power electronic test platform for characterizing magnetocaloric materials.

  • 18.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Design of Permanent-Magnet Linear Generators with Constant-Torque-Angle Control for Wave Power2019In: Energies, E-ISSN 1996-1073, Vol. 12, no 7, article id 1312Article in journal (Refereed)
    Abstract [en]

    This paper presents a simulation method for direct-drive permanent-magnet linear generators designed for wave power. Analytical derivations of power and maximum damping force are performed based on Faraday's law of induction and circuit equations for constant-torque-angle control. Knowledge of the machine reactance or the load angle is not needed. An aim of the simulation method is to simplify comparison of the maximum damping force, losses, and cost between different generator designs at an early design stage. A parameter study in MATLAB based on the derived equations is performed and the effect of changing different generator parameters is studied. The analytical calculations are verified with finite element method (FEM) simulations and experiments. An important conclusion is that the copper losses and the maximum damping force are mainly dependent on the rated current density and end winding length. The copper losses are inherently large in a slow-moving machine so special consideration should be taken to decrease the end winding length. It is concluded that the design of the generator becomes a trade-off between material cost versus high efficiency and high maximum damping force.

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  • 19.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Inherent Difference in Saliency for Generators with Different PM Materials2014In: Journal of Renewable Energy, ISSN 2314-4386, E-ISSN 2314-4394, Vol. 2014, p. 567896,-Article in journal (Refereed)
    Abstract [en]

    The inherent differences between salient and nonsalient electrical machines are evaluated for two permanent magnet generators with different configurations. The neodymium based (NdFeB) permanent magnets (PMs) in a generator are substituted with ferrite magnets and the characteristics of the NdFeB generator and the ferrite generator are compared through FEM simulations. The NdFeB generator is a nonsalient generator, whereas the ferrite machine is a salient-pole generator, with small saliency. The two generators have almost identical properties at rated load operation. However, at overload the behaviour differs between the two generators. The salient-pole, ferrite generator has lower maximum torque than the NdFeB generator and a larger voltage drop at high current. It is concluded that, for applications where overload capability is important, saliency must be considered and the generator design adapted according to the behaviour at overload operation. Furthermore, if the maximum torque is the design criteria, additional PM mass will be required for the salient-pole machine.

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  • 20.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Permanent Magnet Synchronous Machines2019In: Energies, E-ISSN 1996-1073, Vol. 12, no 14, article id 2830Article in journal (Other academic)
    Abstract [en]

    Interest in permanent magnet synchronous machines (PMSMs) is continuously increasing worldwide, especially with the increased use of renewable energy and electrification of transports. This special issue contains the successful invited submissions of fifteen papers to a Special Issue of Energies on the subject area of Permanent Magnet Synchronous Machines. The focus is on permanent magnet synchronous machines and the electrical systems they are connected to. The presented work represents a wide range of areas. Studies of control systems, both for permanent magnet synchronous machines and for brushless DC motors, are presented and experimentally verified. Design studies of generators for wind power, wave power and hydro power are presented. Finite element method simulations and analytical design methods are used. The presented studies represent several of the different research fields on permanent magnet machines and electric drives.

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  • 21.
    Eriksson, Sandra
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    Vertical Axis Wind Turbines with Direct Driven Generators2006Licentiate thesis, monograph (Other scientific)
  • 22.
    Eriksson, Sandra
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    Generator-Damped Torsional Vibrations of a Vertical Axis Wind Turbine2006In: Wind Engineering, Vol. 29, no 5Article in journal (Refereed)
  • 23.
    Eriksson, Sandra
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Loss evaluation and design optimisation for direct driven permanent magnet synchronous generators for wind power2011In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 88, no 1, p. 265-271Article in journal (Refereed)
    Abstract [en]

    When designing a generator for a wind turbine it is important to adapt the generator to the source, i.e. the wind conditions at the specific site. Furthermore, the variable speed operation of the generator needs to be considered. In this paper, electromagnetic losses in direct driven permanent magnet synchronous generators are evaluated through simulations. Six different generators are compared to each other. The simulations are performed by using an electromagnetic model, solved in a finite element environment and a control model developed in MATLAB. It is shown that when designing a generator it is important to consider the statistical wind distribution, control system, and aerodynamic efficiency in order to evaluate the performance properly. In this paper, generators with high overload capability are studied since they are of interest for this specific application. It is shown that a generator optimised for a minimum of losses will have a high overload capability.

  • 24.
    Eriksson, Sandra
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rotor design for PM generators reflecting the unstable neodymium price2012In: Electrical Machines (ICEM), 2012 XXth International Conference, 2012, p. 1419-1423Conference paper (Refereed)
    Abstract [en]

    The price of rare earth metals such as neodymium is very unstable and has in recent years increased more than 1000%. This leaves the wind power business that uses permanent magnet generators with large insecurity. In this paper, a generator design with an interchangeable rotor is presented, which gives the option of having a rotor with different material depending on the current neodymium price. Thereby, the wind turbine has the same properties with only the generator rotor changing. The suggested alternative, a ferrite rotor, is much heavier than a neodymium rotor. The heavy ferrite rotor indicates an advantage for the vertical axis wind turbine technology with the generator placed on ground level, where the weight is not as important as in the hub. Two similar generator designs are presented, magnet material differences are discussed and the neodymium price limit for when the ferrite rotor is to be preferred is calculated.

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  • 25.
    Eriksson, Sandra
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bergkvist, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Design of a unique direct driven PM generator adapted for a telecom tower wind turbine2012In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 44, p. 453-456Article in journal (Refereed)
    Abstract [en]

    A vertical axis wind turbine has been designed to electrify a novel kind of telecommunication tower. This paper presents the design of a generator for this purpose. The generator is a permanent magnet generator rated at 10 kW. It has an unusually large diameter to fit on the outside of the telecommunication tower. The generator has been designed by using a two-dimensional FEM model. Simulations show that the generator has high efficiency through the whole operational interval. Furthermore, the generator has a high overload capability enabling electric control of the turbine. The generator has been built and the design shown feasible. Preliminary experimental results show that the induced voltage is lower than expected from simulations indicating insufficient modelling of three-dimensional effects, which are particularly large in a generator with these unusual dimensions.

  • 26.
    Eriksson, Sandra
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A 225 kW Direct Driven PM Generator Adapted to a Vertical Axis Wind Turbine2011In: Advances in Power Electronics, ISSN 2090-181X, Vol. 2011, p. 239061-Article in journal (Refereed)
    Abstract [en]

    A unique direct driven permanent magnet synchronous generator has been designed and constructed. Results from simulations as well as from the first experimental tests are presented. The generator has been specifically designed to be directly driven by a vertical axis wind turbine and has an unusually low reactance. Generators for wind turbines with full variable speed should maintain a high efficiency for the whole operational regime. Furthermore, for this application, requirements are placed on high generator torque capability for the whole operational regime. These issues are elaborated in the paper and studied through simulations. It is shown that the generator fulfils the expectations. An electrical control can effectively substitute a mechanical pitch control. Furthermore, results from measurements of magnetic flux density in the airgap and no load voltage coincide with simulations. The electromagnetic simulations of the generator are performed by using an electromagnetic model solved in a finite element environment.

  • 27.
    Eriksson, Sandra
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Evaluation of different turbine concepts for wind power2008In: Renewable and Sustainable Energy Reviews, Vol. 12, no 5, p. 1419-1434Article in journal (Refereed)
  • 28.
    Eriksson, Sandra
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    FEM simulations and experiments of different loading conditions for a 12 kW direct driven PM synchronous generator for wind power2009In: International Journal of Emerging Electric Power Systems, ISSN 2194-5756, E-ISSN 1553-779X, Vol. 10, no 1, p. 3-Article in journal (Refereed)
    Abstract [en]

    Results from experiments on a direct driven permanent magnet synchronous generator are presented. Dynamic simulations have been performed using the finite element method in order to study the generator. The simulations are performed by using an electromagnetic model, which is described by a combined field and circuit equation model and is solved in a finite element environment. The stator winding of the generator consists of circular cables and the rotor has surface-mounted, arched, permanent magnets. A complete experimental setup has been used consisting of a motor, a frequency converter, a gearbox and electrical loads. The generator is connected to a purely resistive load. Measurements have been performed for different rotational speeds and different loads. Furthermore, the generator has been studied for the realistic wind turbine loading conditions for operation at the optimum tip speed ratio. The variable speed operation in a wind turbine is evaluated and discussed. The agreement between experimental results and simulations based on finite element calculations is high, indicating precise simulations. The measurement errors are calculated and discussed. Furthermore, other sources of error are suggested and discussed that could explain the differences between the simulations and the measured data. 2009 The Berkeley Electronic Press. All rights reserved.

  • 29.
    Eriksson, Sandra
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Eklund, P.
    Halmstad Univ, Rydberg Lab Appl Sci, POB 823, SE-30118 Halmstad, Sweden..
    Effect of magnetic properties on performance of electrical machines with ferrite magnets2021In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 54, no 5, article id 054001Article in journal (Refereed)
    Abstract [en]

    The increased focus on ferrite magnets makes it interesting to investigate their suitability in electrical machines such as generators for wind power and motors for electric cars. Efforts are currently being made to improve the magnetic properties of ferrites. A simulation method is used to investigate how different magnetic properties such as remanence, coercivity and intrinsic coercivity affect the performance of electrical machines, here quantified as output torque. It is also ensured that the magnet is not partly demagnetized during a short-circuit event. Simulations are performed through a two-dimensional finite-element-based simulation method. Not all combinations of magnetic properties will render a usable design and it is therefore investigated how high the required values are for different magnetic properties as well as how high an output torque can be achieved. It is concluded that increasing the remanence or the coercivity can be quantified as an improved energy product, whereas improvement of the intrinsic coercivity enables the magnet to have a more optimal shape and thereby have a working point where the energy product is maximized. In addition it is found that for a fixed available magnetic energy, the performance does not change significantly with increasing remanence.

  • 30.
    Eriksson, Sandra
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kjellin, Jon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Tip Speed ratio control of a 200 kW VAWT with synchronous generator and variable DC voltage2013In: Energy Science & Engineering, ISSN 2050-0505, Vol. 1, no 3, p. 135-143Article in journal (Refereed)
    Abstract [en]

    A novel control method for a fixed-pitch variable speed wind turbine is introduced and experimental results are presented. The measured absorbed power and rotational speed, together with a look-up table for the aerodynamic efficiency, are used to estimate the wind speed reaching the turbine as well as the tip speed ratio. Thereby, the control is independent on wind speed measurements and the wind turbine itself is used as an anemometer. Tip speed ratio control is implemented by comparing the estimated tip speed ratio to a reference value and adjusting the DC voltage level accordingly. Tip speed ratio control benefits from that the aerodynamic efficiency hardly varies with changing tip speed ratio when close to its optimum value. Experimental results from a 200 kW vertical axis wind turbine are presented. The voltage from the permanent magnet generator is passively rectified and the alternating DC voltage is then inverted, filtered, transformed, and grid connected. The estimated wind speed is compared with the measured wind speed. The absorbed power when tip speed ratio control has been implemented is shown. It is concluded that the presented control method works and some future improvements are discussed.

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  • 31.
    Eriksson, Sandra
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Semberg, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A 225 kW direct driven PM generator for a vertical axis wind turbine2010In: European Wind Energy Conference & Exhibition, Warsaw, Poland, 2010Conference paper (Refereed)
  • 32.
    Eriksson, Sandra
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Semberg, Tobias
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Gerador de ímãs permanentes de acionamento direto para turbina de eixo vertical2011In: Eletricidade Moderna, ISSN 0100-2104, p. 160-165Article in journal (Refereed)
  • 33.
    Eriksson, Sandra
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Silva, Marcelo D.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Comparison of Simulation Methods for Angular Dependency when Modeling Demagnetization2023In: 2023 IEEE International Magnetic Conference, INTERMAG, Institute of Electrical and Electronics Engineers (IEEE), 2023Conference paper (Refereed)
    Abstract [en]

    Rare earth element free magnets, such as ferrites, are weaker than their more common alternatives and therefore more prone to demagnetization. Additionally, in permanent magnet electrical machines they are commonly tangentially magnetized and placed in a spoke-type geometry to enhance the magnetic field. In this geometry, the magnets are subject to inclined fields, which are normally not accounted for when evaluating demagnetization risk. In this paper, different methods for demagnetization of permanent magnets are applied to two motors under two distinct loading conditions and the results are compared. It is concluded that it is more important to consider inclined fields when studying ferrite magnets than rare earth element magnets. The common, simplified method of omitting inclined fields is shown to be the most conservative method for evaluating demagnetization. However, more precise results can be reached with methods taking inclined fields into account, especially if the models are adapted for the specific magnet type. Two motors with similar performance have been designed, one with rare earth element magnets and one with ferrites. The motor with ferrites is more sensitive to demagnetization and the bulk of the magnet reaches the demagnetization limit at a lower current than for the motor with rare earth element-based magnets. Finally, demagnetization of magnets is compared for two different rotor positions, emphasizing the importance of considering rotor position when evaluating demagnetization risk.

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  • 34.
    Eriksson, Sandra
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Solum, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Simulations and experiments on a 12 kW direct driven PM synchronous generator for wind power2008In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 33, no 4, p. 674-681Article in journal (Refereed)
    Abstract [en]

    A direct driven permanent magnet (PM) synchronous generator has been designed and constructed and results from the first experimental tests are presented. The generator has been designed using the finite element method (FEM) and dynamic simulations have been performed to study the generator. The simulations are performed by using an electromagnetic model, which is described by a combined field and circuit equation model and is solved in a finite element environment. The stator winding of the generator consists of circular cables and the rotor has surface mounted, arched PMs. A complete experimental setup has been constructed consisting of a motor, a frequency converter, a gearbox and electrical loads. Oscilloscopes are used to measure the voltage and the current for each phase. Measurements have been performed for both full load and no load at rated speed. The harmonic content of the voltage is analyzed and compared to results from simulations. Furthermore, the generated electric power has been calculated from knowing the voltage and current and is compared to the simulated power. The agreement between experimental results and results from simulations based on finite element calculations is very high.. especially considering harmonics. Several sources of error are suggested that could cause the small differences between the simulated results and the measured data for the constructed generator.

  • 35.
    Frost, Anna E.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Sjölund, Jonathan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Imperfections in the air gap and the permanent magnets of linear synchronous permanent magnet generators for wave power2021In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059Article in journal (Other academic)
  • 36.
    Frost, Anna E.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Sjölund, Jonathan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Power flow in the air gap of linear electrical machines by utilization of the Poynting vector: Part 2 - Simulations2022In: The Journal of Engineering, E-ISSN 2051-3305, Vol. 2022, no 9, p. 883-891Article in journal (Refereed)
    Abstract [en]

    Different types of linear generators are simulated and their power flow in the air gap is investigated. The results are compared to the analytical expressions derived in Part 1. The simulations and the analytical expressions in Part 1 show the same general behavior, but the magnitudes are lower for the analytical expressions. One explanation for the difference in magnitude can be that the harmonics of the electric and magnetic fields contribute to the power flow, which is not accounted for in the analytical expressions. Due to results from Part 1, it is investigated if changing the number of poles can decrease the tangential power flow while the normal power flow stays the same. As was suspected, changing the number of poles affected several other factors, which lead to an increase in the normal power flow when increasing the number of poles, even though the electrical power was the same. The tangential power flow also decreased for three out of four generators. Thereby, increasing the number of poles with the same length of the machine, at the cost of reduced pole-pitch, should be done with precaution.

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  • 37.
    Frost, Anna E.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Temiz, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Power flow in the air gap of linear electrical machines by utilization of the Poynting vector: Part 1 - Analytical expressions2022In: The Journal of Engineering, E-ISSN 2051-3305, Vol. 2022, no 4, p. 377-388Article in journal (Refereed)
    Abstract [en]

    Analytical solutions and estimations for the power flow in the air gap of linear electrical machines of different geometries are derived from Poynting's theorem. The different geometries considered are flat one-sided, multi-sided, and tubular linear electrical machines. The radial power flow for all considered geometries is dependent on the area of the air gap, the electric field, the magnetic field, and the load angle. The tangential power flow for both flat one-sided and tubular linear electrical machines is dependent of the area of the air gap, number of poles, the electric field, the magnetic field, and the load angle. The number of poles could be increased to decrease the tangential power flow in flat linear electrical machines. The expression for the tangential flow in tubular linear electrical machines is so complicated that it is difficult to draw conclusions from it.

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  • 38.
    Frost, Anna E.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ulvgård, Liselotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Uppsala University.
    Sjökvist, Linnea
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Partial Stator Overlap in a Linear Generator for Wave Power: An Experimental Study2017In: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 5, no 4, article id 53Article in journal (Refereed)
    Abstract [en]

    This paper presents a study on how the power absorption and damping in a linear generator for wave energy conversion are affected by partial overlap between stator and translator. The theoretical study shows that the electrical power as well as the damping coefficient change quadratically with partial stator overlap, if inductance, friction and iron losses are assumed independent of partial stator overlap or can be neglected. Results from onshore experiments on a linear generator for wave energy conversion cannot reject the quadratic relationship. Measurements were done on the inductance of the linear generator and no dependence on partial stator overlap could be found. Simulations of the wave energy converter's operation in high waves show that entirely neglecting partial stator overlap will overestimate the energy yield and underestimate the peak forces in the line between the buoy and the generator. The difference between assuming a linear relationship instead of a quadratic relationship is visible but small in the energy yield in the simulation. Since the theoretical deduction suggests a quadratic relationship, this is advisable to use during modeling. However, a linear assumption could be seen as an acceptable simplification when modeling since other relationships can be computationally costly.

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  • 39.
    Grabbe, Mårten
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    On the Stator Slot Geometry of a Cable Wound Generator for Hydrokinetic Energy Conversion2015In: Scientific World Journal, E-ISSN 1537-744X, article id 812149Article in journal (Refereed)
    Abstract [en]

    In this paper, the stator slot geometry of a cable wound permanent magnet synchronous generator for hydro-kinetic energy conversion is evaluated. When designing generators, practical experience is of great importance to result in a realizable design. Therefore, practical experience from winding two cable wound generators is used to propose optimized dimensions of different parts in the stator slot geometry. A thorough investigation is performed through simulations of how small geometrical changes alter the generator performance. Simulations are performed by using the finite element method (FEM) to solve coupled field and circuit equations. The parameter study shows that small changes in the geometry can have large affect on the performance and the generator dimensions. Furthermore, it is concluded that the load angle is especially sensitive to small geometrical changes. A new generator design is proposed which shows improved efficiency, reduced weight and a possibility to decrease the expensive permanent magnet material by almost one fifth.

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  • 40.
    Ibrayeva, Anar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Dynamic Modeling of a Generator With Anisotropic Nonlinear Permanent Magnets in Finite Element Method Software2023In: IEEE Transactions on Magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 59, no 9, article id 7401308Article in journal (Refereed)
    Abstract [en]

    In this article, a method of dynamic modeling of nonlinear permanent magnets (PMs) with recoil lines in 2-D finite element analysis (FEA) software was presented. COMSOL Multiphysics 6.0 FEA software was used in this study. The method is implemented through the variable utilities. The simulation results of a spoke-type synchronous generator for a wind turbine with anisotropic aluminum-nickel-cobalt (Alnico) 5, 8B, and 9 grades were used to exemplify the model and compared. The proposed methodology can be used for the simulation of nonlinear PMs with recoil lines and includes reversible and irreversible losses of magnetization of nonlinear PMs. The effect of the magnetic field from the stator winding on nonlinear PMs during normal operation and short circuits was studied. The modeling results were compared to the model without any demagnetization and a previous study with recoil lines and averaged minimum magnetic flux points. The no-load (NL) voltages were compared before and after a demagnetization. The dynamic model showed considerable demagnetization of Alnico magnets during normal operational and three-phase short circuits. Alnico 5 and 9 showed higher sensitivity to short-circuit currents and the short-circuit currents caused remagnetization of the upper part of the magnet in the opposite direction. The anisotropy of the PM implemented in the model improved the magnetic field simulation inside the magnet and partially protected the magnet from demagnetization by inclined fields. At last, the method was experimentally verified by tests on an iron core.

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    FULLTEXT01
  • 41.
    Ibrayeva, Anar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Lind, Emil
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Silva, Marcelo D.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Ghorai, Sagar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Measurement and Modelling of Hysteresis Curves for Nonlinear Permanent Magnets at Different Inclination Angles2023In: 2023 IEEE International Magnetic Conference (INTERMAG), Institute of Electrical and Electronics Engineers (IEEE), 2023Conference paper (Refereed)
    Abstract [en]

    This paper presents the measurement results of the BH/MH curves of the Alnico 8 (LNGT40) with recoil loops and a mathematical model for the calculation of the average magnetic flux density in a cubic permanent magnet. The measurements were performed with a Vibrating Sample Magnetometer (VSM). The magnet samples have a cubic shape with 3 mm sides. BH curves in preferred (easy) and transverse directions and recoil loops were measured and compared to Alnico 9 (LNGT72) as well as to the data from the supplier. The load line of the cubic magnet in 0 A/m applied magnetic field was found. A mathematical model was developed which can approximate the MH a curve for an applied field with an arbitrarily chosen angle between the field and easy axis, given MH a curves for 0o and 90o. Also, a simplified general model of a cubic permanent magnet in the air and calculation results of stored energy and hysteresis losses were presented.

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    INTERMAG2023
  • 42.
    Ibrayeva, Anar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Lopez, Fausto
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Modelling of Permanent Magnet Synchronous Generator with Non-linear Magnets2021In: 2021 22nd IEEE International Conference on Industrial Technology (ICIT), IEEE Institute of Electrical and Electronics Engineers (IEEE), 2021, p. 209-214Conference paper (Refereed)
    Abstract [en]

    In this paper simulation results of a spoke-type synchronous generator for a wind turbine with three different grades of Alnico magnets were presented. COMSOL Multiphysics 5.4 finite element analysis (FEA) based software was used. The proposed model was used for simulation of a synchronous generator with non-linear Alnico magnets with recoil-lines with some approximations and can be used for modelling electrical machines with other non-linear permanent magnets. The geometry of the machines was kept fixed for all scenarios. The model takes into account the irreversible loss of magnetization of non-linear permanent magnets due to the magnetic field from the stator winding during normal operation and short circuit. Modelling results show that Alnico 5 (ArKomax800) magnets have the lowest output power, but they are the least sensitive to change of the load. The generator with Alnico 8 permanent magnets have the highest output power, is good at handling the nominal load but the most sensitive to short circuits. Alnico 9 magnets could be an option if the risk for short circuits is accounted for.

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  • 43.
    Kjellin, Jon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bülow, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Deglaire, Paul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Power coefficient measurement on a 12 kW straight bladed vertical axis wind turbine2011In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 36, no 11, p. 3050-3053Article in journal (Refereed)
    Abstract [en]

    A 12 kW vertical axis H-rotor type wind turbine has been designed and constructed at Uppsala University. A measurement campaign has been performed to collect data to calculate the power coefficient using the method of bins. The measurement was performed at different constant rotational speeds on the turbine during varying wind speeds to observe the power coefficients dependence on tip speed ratio. The power coefficient peaked at 0.29 for a tip speed ratio equal to 3.3.

  • 44.
    Kjellin, Jon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Electric Control Substituting Pitch Control for Large Wind Turbines2013In: Journal of Wind Energy, Vol. 2013, p. 4-Article in journal (Refereed)
    Abstract [en]

    A completely electrical control of a variable speed wind turbine is experimentally verified. A vertical axis wind turbine with a direct driven generator and an electrical system with diode rectification and full inverter connected to the electric grid is presented. This is the first paper that presents this novel 200 kW wind power plant erected at the west coast of Sweden. The turbine has fixed pitch and is only controlled electrically accommodated by passive stall of the blades. By electrically controlling the generator rotational speed with the inverter, passive stall regulation is enabled. The first results on experimental verification of stall regulation in gusty wind speeds are presented. The experiments show that the control system can keep the turbine rotational speed constant even at very gusty winds. It is concluded that electrical control accommodated by passive stall is sufficient as control of the wind turbine even at high wind speeds and can substitute mechanical control such as blade pitch.

  • 45.
    Kjellin, Jon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Deglaire, Paul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bülow, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Progress of control system and measurement techniques for a 12 kW vertical axis wind turbine2008Conference paper (Refereed)
  • 46.
    Kontos, Sofia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Ibrayeva, Anar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Leijon, Jennifer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Mörée, Gustav
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Frost, Anna E.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Schönström, Linus
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity. Division of Electrical Machines and Power Electronics, Chalmers University of Technology, 412 96 Göteborg, Sweden.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    An Overview of MnAl Permanent Magnets with a Study on Their Potential in Electrical Machines2020In: Energies, E-ISSN 1996-1073, Vol. 13, no 21, article id 5549Article in journal (Refereed)
    Abstract [en]

    In this paper, hard magnetic materials for future use in electrical machines are discussed. Commercialized permanent magnets used today are presented and new magnets are reviewed shortly. Specifically, the magnetic MnAl compound is investigated as a potential material for future generator designs. Experimental results of synthesized MnAl, carbon-doped MnAl and calculated values for MnAl are compared regarding their energy products. The results show that the experimental energy products are far from the theoretically calculated values with ideal conditions due to microstructure-related reasons. The performance of MnAl in a future permanent magnet (PM) generator is investigated with COMSOL, assuming ideal conditions. Simplifications, such as using an ideal hysteresis loop based on measured and calculated saturation magnetization values were done for the COMSOL simulation. The results are compared to those for a ferrite magnet and an NdFeB magnet. For an ideal MnAl hysteresis loop, it would be possible to replace ferrite with MnAl, with a reduced weight compared to ferrite. In conclusion, future work for simulations with assumptions and results closer to reality is suggested.

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  • 47.
    Leijon, Jennifer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Sjölund, Jonathan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ekergard, Boel
    Seabased Ind AB, Verkstadsgatan 4, S-45330 Lysekil, Sweden..
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Temiz, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Study of an Altered Magnetic Circuit of a Permanent Magnet Linear Generator for Wave Power2018In: Energies, E-ISSN 1996-1073, Vol. 11, no 1, article id 84Article in journal (Refereed)
    Abstract [en]

    The wave energy converter (WEC) studied and developed at Uppsala University in Sweden is a point absorbing buoy connected to a linear generator (LG) on the seabed. Previous studies have improved the sustainability of the generator, changing its magnets from Nd2Fe14B-magnets to ferrites. In this paper, the magnetic circuit of the linear generator is further studied. Ferrite magnets of two different types (Y30 and Y40) are studied along with different shapes of pole shoes for the system. The finite element method (FEM) simulations in a program called Ace are performed. The results show that a linear generator including both Y30 and Y40 magnets and shortened T-shaped pole shoes can generate a similar magnetic energy in the airgap as a linear generator only containing Y40 magnets and rectangular pole shoes. This shows that the magnetic circuit can be altered, opening up sizes and strengths of magnets for different retailers, and thereby possibly lowering magnet cost and transportation. This work was previously presented as a conference at the European Wave and Tidal Energy Conference (EWTEC) 2017 in Cork, Ireland; this manuscript has been carefully revised and some discussions, on magnet costs for example, have been added to this paper.

  • 48.
    Leijon, Mats
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ekergård, Boel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Apelfröjd, Senad
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    de Santiago, Juan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    On a Two Pole Motor for Electric Propulsion System2013In: International Journal of Engineering Science and Innovative Technology, ISSN 2319 - 5967, Vol. 2, no 1, p. 99-111Article in journal (Refereed)
  • 49.
    Lind, Emil
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Bergman, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Effect of Drive Cycle Quantification on Electric Motor Efficiency2023In: 12th International Conference on Power Electronics, Machines and Drives (PEMD 2023), Institution of Engineering and Technology, 2023, Vol. 12, p. 96-104Conference paper (Refereed)
    Abstract [en]

    One way to evaluate real life electric vehicle performance is through drive cycle analysis. However, performing Finite Element Method (FEM) analysis is computationally heavy and optimisation of motor efficiency across all operating points using FEM is time demanding. One way to solve this is by changing the resolution of the drive cycle. The objective of this study is to investigate how different resolutions affect the results, specifically in terms of energy, losses and overall drive cycle efficiency. This study shows, through both analytical calculations and FEM simulations, that it is possible to greatly decrease the number of operating points with only a minimal impact on the overall drive cycle efficiency. There does not seem to exist a universal rule to this which span different drive cycles. However, the quantifications of all drive cycles exhibit a similar pattern, with increased efficiency instability for lower resolutions. For the Worldwide Harmonised Light Vehicles Test Procedure drive cycle, a decrease of 6.4 times in operating points only affects the maximum efficiency deviation by 0.036 percentage points. At this resolution, over half of the energy is distributed along only 25 points, making these a good starting point for electric motor design and optimisation.

  • 50.
    Möllerström, Erik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Department of Construction and Energy Engineering, Halmstad University, PO Box 823, SE-301 18 Halmstad, Sweden.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ottermo, Fredric
    Department of Construction and Energy Engineering, Halmstad University, PO Box 823, SE-301 18 Halmstad, Sweden.
    Hylander, Jonny
    Department of Construction and Energy Engineering, Halmstad University, PO Box 823, SE-301 18 Halmstad, Sweden.
    Turbulence influence on optimum tip speed ratio for a 200 kW vertical axis wind turbine2016In: Science Of Making Torque From Wind (Torque 2016) / [ed] IOP, 2016, Vol. 753, article id 032048Conference paper (Refereed)
    Abstract [en]

    The influence of turbulence intensity (TI) on the tip speed ratio for maximum power coefficient, here called λCp-max, is studied for a 200 kW VAWT H-rotor using logged data from a 14 month period with the H-rotor operating in wind speeds up to 9 m/s. The TI - λCp-max relation is examined by dividing 10 min mean values in different turbulence intensity ranges and producing multiple CP(λ) curves. A clear positive relation between TI and λCp-max is shown and is further strengthened as possible secondary effects are examined and deemed non-essential. The established relation makes it possible to tune the control strategy to enhance the total efficiency of the turbine.

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