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  • 1.
    Bladh, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wallin, Mattias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Saarinen, Linn
    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.
    Standstill Frequency Response Test on a Synchronous Machine Extended With Damper Bar Measurements2016In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 31, no 1, p. 46-56Article in journal (Refereed)
    Abstract [en]

    Standstill Frequency Response (SSFR) test data from a salient-pole synchronous machine with reconfigurable damper winding is presented. In addition to the regular measurements, the damper bar currents are measured and used to obtain the stator-to-damper transfer functions. The test is performed three times with physically different damper winding configurations. An extension to the standard SSFR test analysis scheme is suggested where the stator-to-damper transfer functions are included. The validity of the identified models is substantiated by comparison of the simulated and measured machine response to a drive torque step disturbance. It is found that the damper winding measurements can be incorporated in the analysis scheme to isolate the effect of the damper circuits. However, for a machine of the type studied, also the standard SSFR test produce yields models that are accurate enough for power system studies.

  • 2.
    Dahlborg, Elin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering.
    Norrlund, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity. Vattenfall AB, Älvkarleby Laboratory, Älvkarleby, SE, Sweden.
    Saarinen, Linn
    Vattenfall Hydropower AB, Uppsalavägen 3, Älvkarleby, SE, Sweden.
    Kaplan turbine model validation for large grid frequency disturbances2021In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 36, no 2, p. 611-618Article in journal (Refereed)
    Abstract [en]

    The grid frequency stability is decreasing in many AC grids due to less inertia in these systems, and their stability is commonly evaluated through simulation. Hydropower often delivers frequency control, yet research on hydropower model validation for large grid frequency disturbances is scarce. We performed frequency control tests on a Kaplan unit and evaluated three models (called the standard grey-box, Kaplan grey-box, and white-box models) against validation data. The grey-box model parameters were identified with grey-box system identification, whereas the white-box model used index test data to relate guide vane opening and runner blade angle to net head, flow, and efficiency. All models accounted for steering mechanism backlash. The results showed that the white-box model was overall more reliable than the two grey-box models. However, all models had difficulties in simulating the output power the first few seconds after a large change in frequency. Moreover, backlash sizes had considerable performance impacts on all models. The uncertainties in hydropower model response during the first few seconds after a disturbance emphasize the importance of sufficient stability margins in grid frequency stability simulations. 

  • 3.
    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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  • 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.
    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)
  • 6.
    Laban, Danilo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity. Fortum Sverige AB, SE-16968 Solna, Sweden..
    Norrlund, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis. Vattenfall AB, Alvkarleby Lab, SE-81426 Alvkarleby, Sweden..
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Storage System Design for Improved Primary Frequency Control From Hydropower Units2023In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 38, no 3, p. 1836-1844Article in journal (Refereed)
    Abstract [en]

    The upcoming modifications to the criteria for providing Frequency Containment Reserves (FCR) in the Nordic synchronous area present severe challenges for some hydropower units. By quantifying the difference between the required FCR power response and the actual response provided by the unit, an additional power response from an energy storage system can be specified to augment the hydropower unit, thus securing its participation in FCR in the future. A practical method to control the storage system, by applying a band-pass filter on the negative frequency deviation, is presented in this paper. The method is verified using a set of field measurements from Swedish hydropower units currently providing FCR. It is found that all tested units are able to satisfy the upcoming criteria with the specified storage systems. The optimality of the method is discussed by comparing the storage system power and energy ratings to the theoretical minimum. Obtained power ratings between 3% and 24% of the FCR power, combined with a short storage system duration of up to 2.5 minutes, indicate that the method presents a possible application for high-power and low-energy storage technologies.

  • 7. Lidenholm, Johan
    et al.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Estimation of Hydropower Generator Parameters Through Field Simulations of Standard Tests2010In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 25, no 4, p. 931-939Article in journal (Refereed)
    Abstract [en]

    Four standard test procedures-the three phase short-circuit test, the field decrement test, the slip test, and the applied voltage test-for estimation of synchronous generator parameters have been implemented in a time-stepping finite-element software. In this paper, the main features of the implementation and the post-processing of data are described. The validity of the application is demonstrated by comparison with test results from the commissioning of a large hydropower generator. The method is shown to be effective in estimating most parameters. Better representation of the exciter and the interpole connections of the damper circuit is believed to enhance the compliance even further.

  • 8.
    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.

  • 9.
    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.

  • 10.
    Nøland, Jonas Kristiansen
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hjelmervik, Karina Bakkeløkken
    Buskerud and Vestfold University College.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Comparison of Thyristor-Controlled Rectification Topologies for a Six-Phase Rotating Brushless Permanent Magnet Exciter2016In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 31, no 1, p. 314-322Article in journal (Refereed)
    Abstract [en]

    The thyristor bridge rectifier has proven to be a reliable solution regarding control of excitation equipment for synchronous generators. However, in rotating brushless exciters, the diode rectifier is the dominant topology on the shaft. In order to improve the step response of rotating exciters, one could put a thyristor bridge rectifier on the rotating part and control the firing angle remotely from a stationary controller. This paper compares different multiphase configurations of permanent magnet synchronous machines as a rotating exciter and discusses the possibility to reduce the torque ripple by selecting the appropriate rectification topology. The paper also explains the implications of the self and mutual inductances of the armature windings for the performance of the exciter.

  • 11.
    Ranlöf, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Perers, Richard
    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.
    On Permeance Modeling of Large Hydrogenerators With Application to Voltage Harmonics Prediction2010In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 25, no 4, p. 1179-1186Article in journal (Refereed)
    Abstract [en]

    In this paper, a permeance model that can be employed to estimate the no-load damper current loss and voltage waveform harmonics in large hydrogenerators is presented. The importance of modeling the damper magnetomotive force and inductances correctly is emphasized, and detailed descriptions are presented. The computed harmonics are compared with values obtained from time-stepped finite-element calculations and measured data. The results are in good agreement. The influence of pole-to-pole damper bar connections, and of the number of damper bars on the voltage waveform, is explained.

  • 12.
    Rossander, Morgan
    et al.
    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.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Mechanical torque ripple from a passive diode rectifier in a 12 kW vertical axis wind turbine2017In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 32, no 1, p. 164-171Article in journal (Refereed)
    Abstract [en]

    The influence of passive rectification on the mechanical torque of a permanent magnet generator for a directly driven vertical axis wind turbine has been studied. Passive diode rectification introduce electromagnetic torque ripple from the generator. The conversion of electromagnetic torque ripple into mechanical torque ripple and rotational speed ripple has been modeled, analytically evaluated, and simulated. The simulations have been compared to measurements on an open site 12 kW prototype. A parameter study with the model illustrates the impact of shaft torsional spring constant, generator rotor inertia, generator inductance, and dc-link capacitance. The results show that the shaft and generator rotor can be an effective filter of electromagnetic torque ripple from diode rectification. The measured mechanical torque ripple amplitude on the prototype is less than +/- 0.9% of nominal turbine torque. The measurements compare well with the simulations.

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  • 13.
    Saarinen, Linn
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Norrlund, Per
    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.
    Field Measurements and System Identification of Three Frequency Controlling Hydropower Plants2015In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 30, no 3, p. 1061-1068Article in journal (Refereed)
    Abstract [en]

    The dynamic behaviour of hydropower plants participating in primary frequency control is investigated in this paper through frequency response, step response and setpoint change tests on three Swedish hydropower plants. Grey-box system identification is used to estimate the parameters of simple linear models suitable for power system analysis and the major shortcomings of the linear models are discussed. It is found that frequency response tests with sinusoidal input signals give more reliable information about the dynamics of the plants than step response tests. It is also shown that backlash in the runner and guide vane regulating mechanisms are of great importance for the dynamic behaviour of the plants, and that the incremental gain from guide vane opening to power varies considerably with the operation point.

  • 14.
    Yang, Weijia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Norrlund, Per
    Bladh, Johan
    Yang, Jiandong
    Lundin, Urban
    Hydraulic damping on rotor angle oscillations: quantification using a numerical hydropower plant modelIn: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059Article in journal (Refereed)
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