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  • 1.
    Abrahamsson, Curt Johan David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Pérez-Loya, Jesús José
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fregelius, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bladh, Johan
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Magnetic thrust bearing for a 10 MW hydropower generator with a Kaplan turbine2018Conference paper (Refereed)
  • 2.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    MANUAL: Flywheel electronics2015Report (Other academic)
    Download full text (pdf)
    fulltext
  • 3.
    Evestedt, Fredrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Pérez-Loya, Jesús José
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Controlling airgap magnetic flux density harmonics in synchronous machines using field current injection2021In: Electrical engineering (Berlin. Print), ISSN 0948-7921, E-ISSN 1432-0487, Vol. 103, p. 195-203Article in journal (Refereed)
    Abstract [en]

    In this paper, a method to control the harmonic content of the magnetic flux density in the airgap of a synchronous machine is presented. Voltage harmonics in one phase as well as the exciting magnetic forces can be affected. Switched power electronics were used to provide the field current to a synchronous machine, the control added specific current harmonics to the DC field current in order to minimize either voltage harmonics or magnetic forces. The method is verified and compared with simulations and experiments on an existing electrical machine.

    Download full text (pdf)
    FULLTEXT01
  • 4.
    Evestedt, Fredrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Pérez-Loya, Jesús José
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Mitigation of Unbalanced Magnetic Pull in Synchronous Machines With Rotating Exciters2021In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 36, no 2, p. 812-819Article in journal (Refereed)
    Abstract [en]

    A magnetization system with active compensation of unbalanced magnetic pull for synchronous machines with rotating exciters is demonstrated. The system used switched power electronics and a digital control system to control the currents in four rotor pole groups, each consisting of 3 poles. It was mounted on the shaft of a synchronous machine, providing an interface between a permanent magnet outer-pole brushless exciter and the segmented field winding. Measurements of magnetic flux density on each pole face and current control made it possible to control the airgap magnetic flux density to balance the machine magnetically, thus removing flux density space harmonics in the airgap and also the unbalanced magnetic pull. The construction of the system is presented along with results from experiments and simulations. Tests were performed with the stator winding both in series and with two parallel circuits. Approximately 80% reduction of static forces and 60% reduction of dynamic forces between the stator and rotor were observed when the system was running.

  • 5.
    Kristiansen Nøland, Jonas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Coll Southeast Norway, Fac Technol Nat Sci & Maritime Sci, N-3184 Borre, Norway.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Pérez-Loya, Jesús José
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Comparison of Thyristor Rectifier Configurations for a Six-Phase Rotating Brushless Outer Pole PM Exciter2018In: IEEE Transactions on Industrial Electronics, ISSN 0278-0046, E-ISSN 1557-9948, Vol. 65, no 2, p. 968-976Article in journal (Refereed)
    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.

  • 6.
    Lundin, Urban
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Pérez, José
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Fregelius, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Nøland, Jonas Kristiansen
    NTNU, Norwegian University of Science and Technology.
    Start of a synchronous motor using rotor field polarity inversion and rotor back-emf sensing2020In: 2020 International Conference on Electrical Machines (ICEM), 2020, Vol. 1, p. 338-344Conference paper (Refereed)
    Abstract [en]

    Synchronous motors are hard to line start due to torque pulsations at zero rotor speed and low starting torque when started using induced current in a damper squirrel cage. By inverting the rotor pole polarity at appropriate times it is possible to, in principle, achieve uniform torque, albeit pulsating with twice the line frequency at zero initial rotor speed. This has been demonstrated in an earlier work. In this paper we demonstrate that high torque starting using the back-emf in the field winding as triggering signal for the rotor polarity inversion is possible. We further discuss the origin of the rotational energy and active and reactive power pulsations. Finally, we show that it is possible to operate a synchronous motors at continuous asynchronous speed by inverting the polarity of the rotor current and adjusting the field current accordingly, although down rated.

  • 7.
    Nøland, Jonas Kristiansen
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Active Current Sharing Control Method for Rotating Thyristor Rectifiers on Brushless Dual-Star Exciters2018In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 33, no 2, p. 893-896Article in journal (Refereed)
    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.

  • 8.
    Nøland, Jonas Kristiansen
    et al.
    Department of Microsystems, University of South-Eastern Norway, Borre, Norway.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Department of Microsystems, University of South-Eastern Norway, Borre, Norway.
    Failure Modes Demonstration and Redundant Postfault Operation of Rotating Thyristor Rectifiers on Brushless Dual-Star Exciters2019In: IEEE Transactions on Industrial Electronics, ISSN 0278-0046, E-ISSN 1557-9948, Vol. 66, no 2, p. 842-851Article in journal (Refereed)
    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.

  • 9.
    Nøland, Jonas Kristiansen
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Pérez-Loya, J. José
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Design and Characterization of a Rotating Brushless Outer Pole PM Exciter for a Synchronous Generator2017In: IEEE transactions on industry applications, ISSN 0093-9994, E-ISSN 1939-9367, Vol. 53, no 3, p. 2016-2027Article in journal (Refereed)
    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.

  • 10.
    Nøland, Jonas Kristiansen
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Coll Southeast Norway, Fac Technol & Maritime Sci, N-3184 Borre, Norway.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Pérez-Loya, Jesus José
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Design and characterization of a rotating brushless PM exciter for a synchronous generator test setup2016In: Design and characterization of a rotating brushless PM exciter for a synchronous generator test setup / [ed] IEEE Xplore, 2016, p. 259-265Conference 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.

  • 11.
    Nøland, Jonas Kristiansen
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Coll Southeast Norway, Dept Engn, Fac Technol & Maritime Sci, N-3184 Borre, Norway.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Pérez-Loya, Jesús José
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Evaluation of different power electronic interfaces for control of a rotating brushless PM exciter2016In: Proceedings Of The IECON 2016 - 42nd Annual Conference of the IEEE Industrial Electronics Society, IEEE, 2016, p. 1924-1929Conference 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.

  • 12.
    Nøland, Jonas Kristiansen
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Coll Southeast Norway, Fac Technol Nat Sci & Maritime Sci, N-3184 Borre, Norway.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Pérez-Loya, Jesús José
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Testing of Active Rectification Topologies on a Six-Phase Rotating Brushless Outer Pole PM Exciter2018In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 33, no 1, p. 59-67Article in journal (Refereed)
    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.

  • 13.
    Perez-Loya, J. Jose
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Initial Performance Tests of a Permanent Magnet Thrust Bearing for a Hydropower Synchronous Generator Test-Rig2016Conference paper (Refereed)
  • 14.
    Pérez-Loya, J. José
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Abrahamsson, C. Johan D.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Demonstration of Synchronous Motor Start by Rotor Polarity Inversion2018In: IEEE Transactions on Industrial Electronics, ISSN 0278-0046, E-ISSN 1557-9948, Vol. 65, no 10, p. 8271-8273Article in journal (Refereed)
    Abstract [en]

    Synchronous motors are reliable and efficient, but it is relatively difficult to start them. In some cases, a variable frequency drive is utilized. In some other, asynchronous start is achieved by virtue of induced currents in a solid rotor, or a rotor damper cage installed for this purpose. In this contribution, a method to start a synchronous machine without a damper cage is presented. The starting was achieved by inverting the polarity of the rotor field winding in a timely manner with respect to the rotating stator field. The technique was verified with experiments performed on a 200 kVA experimental test rig and also simulated on a 20 MVA machine.

  • 15.
    Pérez-Loya, Jesús José
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Performance tests of a permanent magnet thrust bearing for a hydropower synchronous generator test-rig2017In: ACES Journal, Vol. 32, no 8, p. 704-711Article in journal (Refereed)
    Abstract [en]

    Permanent magnets are an attractive material to be utilized in thrust bearings as they offer relatively low losses. If utilized properly, they have a long service lifetime and are virtually maintenance free. In this contribution, we communicate the results of the tests performed on a permanent magnet thrust bearing that was custom built and installed in a hydropower synchronous generator test-rig. Tridimensional finite element simulations were performed and compared with measurements of axial force. Spin down times and axial force ripple have also been measured. We found good correspondence between the measurements and the simulations.

1 - 15 of 15
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  • ieee
  • modern-language-association-8th-edition
  • vancouver
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