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Felicetti, R., Abrahamsson, C. J. & Lundin, U. (2019). Experimentally validated model of a fast switched salient pole rotor winding. In: Experimentally validated model of a fast switched salient pole rotor winding: . Paper presented at 2019 IEEE International Workshop on Electrical Machines Design, Control, and Diagnosis (WEMDCD 2019), Athens, Greece, 22–23 April 2019.
Open this publication in new window or tab >>Experimentally validated model of a fast switched salient pole rotor winding
2019 (English)In: Experimentally validated model of a fast switched salient pole rotor winding, 2019Conference paper, Published paper (Refereed)
Abstract [en]

The article proposes a model of a salient pole synchronous machine field winding based on a single transmission line model. An experimental method to derive the parameters is also presented and validated. Finally, the measured voltage distribution in the winding is compared to the model voltage distribution and the results match, demonstrating the model capabilities. The model describes the intrinsic resonance phenomena and accurately determines the voltage amplification factor.

Keywords
Distributed parameter circuits, eddy currents, parasitic capacitance, resonance, skin effect, stray inductance
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity; Engineering Science; Electrical Engineering with specialization in Systems Analysis
Identifiers
urn:nbn:se:uu:diva-386188 (URN)
Conference
2019 IEEE International Workshop on Electrical Machines Design, Control, and Diagnosis (WEMDCD 2019), Athens, Greece, 22–23 April 2019
Projects
This research has been carried out within the HydroFlex project, which has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 764011.
Funder
EU, Horizon 2020, 764011
Available from: 2019-06-19 Created: 2019-06-19 Last updated: 2019-06-25
Nøland, J. K., Evestedt, F. & Lundin, U. (2019). Failure Modes Demonstration and Redundant Postfault Operation of Rotating Thyristor Rectifiers on Brushless Dual-Star Exciters. IEEE transactions on industrial electronics (1982. Print), 66(2), 842-851
Open this publication in new window or tab >>Failure Modes Demonstration and Redundant Postfault Operation of Rotating Thyristor Rectifiers on Brushless Dual-Star Exciters
2019 (English)In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 66, no 2, p. 842-851Article in journal (Refereed) Published
Abstract [en]

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

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

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

Available from: 2017-11-15 Created: 2017-11-15 Last updated: 2019-05-13Bibliographically approved
Nøland, J. K., Evestedt, F. & Lundin, U. (2018). Active Current Sharing Control Method for Rotating Thyristor Rectifiers on Brushless Dual-Star Exciters. IEEE transactions on energy conversion, 33(2), 893-896
Open this publication in new window or tab >>Active Current Sharing Control Method for Rotating Thyristor Rectifiers on Brushless Dual-Star Exciters
2018 (English)In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 33, no 2, p. 893-896Article in journal (Refereed) Published
Abstract [en]

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

Keywords
AC generator excitation, asymmetrical firing, hybrid-mode 12-pulse thyristor rectifier, brushless exciters
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-333568 (URN)10.1109/TEC.2018.2813664 (DOI)000432993800044 ()
Available from: 2017-11-15 Created: 2017-11-15 Last updated: 2018-08-20Bibliographically approved
Saarinen, L., Norrlund, P., Yang, W. & Lundin, U. (2018). Allocation of Frequency Control Reserves and its Impact on Wear and Tear on a Hydropower Fleet. IEEE Transactions on Power Systems, 33(1), 430-439
Open this publication in new window or tab >>Allocation of Frequency Control Reserves and its Impact on Wear and Tear on a Hydropower Fleet
2018 (English)In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 33, no 1, p. 430-439Article in journal (Refereed) Published
Abstract [en]

Power systems are making a transition from purely technical, centrally planned systems to market based, decentralized systems. The need for balancing power and frequency control reserves are increasing, partially due to variable renewable production, which gives an opportunity for new incomes but also a challenge in terms of changed modes of operation with risk for reduced lifetime for controllable power plants. This paper investigates how the allocation of a sold volume of frequency control reserves within a large hydropower production fleet can affect the costs of providing primary and secondary reserves, in terms of its impact on wear and fatigue, production losses, and the quality of the delivered frequency control. The results show that for primary control, low static gain in the governors results in poor quality and a large amount of load cycles of the units. High static gain, on the other hand, increases the production losses. The control work of the fleet can be reduced by using a proper balance of primary and secondary control gain on each unit, although the intuitive results from linear models exaggerate this effect. Automatic secondary control improves the system frequency quality but also increases the wear.

Keywords
hydropower, frequency control, primary control, reserve allocation, wear and tear
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-308437 (URN)10.1109/TPWRS.2017.2702280 (DOI)000418776400038 ()
Note

Title of this article in dissertation reference lists: Allocation of Frequency Control Reserves and its Impact on Wear on a Hydropower Fleet

Available from: 2016-11-25 Created: 2016-11-25 Last updated: 2018-02-07Bibliographically approved
Yang, W., Sundqvist, P., Saarinen, L., Witt, A., Smith, B., Yang, J. & Lundin, U. (2018). Burden on hydropower units for short-term balancing of renewable power systems. Nature Communications, 9, Article ID 2633.
Open this publication in new window or tab >>Burden on hydropower units for short-term balancing of renewable power systems
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2018 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 2633Article in journal (Refereed) Published
Abstract [en]

There is a general need to change hydropower operational regimes to balance the growing contribution of variable renewable energy sources in power systems. Quantifying the burden on generation equipment is increasingly uncertain and difficult. Here, we propose a framework combining technical and economic indicators to analyze primary frequency control (PFC) on a timescale of seconds. We develop a model integrating hydraulic, mechanical, and electrical subsystems to characterize efficiency loss, wear and fatigue, regulation mileage, and frequency quality. We evaluate burden relief strategies under three idealized remuneration schemes for PFC, inspired by those used in Sweden, the USA, and China, respectively. We show how burden and compensation vary under future scenarios of renewable power systems. Our framework can be used by producers to develop favorable operation strategies that reduce burden and increase economic value, and by transmission system operators to provide insights on the relation between incentive structures and regulating performance.

National Category
Water Engineering
Identifiers
urn:nbn:se:uu:diva-361534 (URN)10.1038/s41467-018-05060-4 (DOI)000437677800010 ()29980673 (PubMedID)
Available from: 2018-09-25 Created: 2018-09-25 Last updated: 2018-09-25Bibliographically approved
Kristiansen Nøland, J., Evestedt, F., Pérez-Loya, J. J., Abrahamsson, J. & Lundin, U. (2018). Comparison of Thyristor Rectifier Configurations for a Six-Phase Rotating Brushless Outer Pole PM Exciter. IEEE transactions on industrial electronics (1982. Print), 65(2), 968-976
Open this publication in new window or tab >>Comparison of Thyristor Rectifier Configurations for a Six-Phase Rotating Brushless Outer Pole PM Exciter
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2018 (English)In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 65, no 2, p. 968-976Article in journal (Refereed) Published
Abstract [en]

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

Keywords
Bridge circuits, Generators, Shafts, Thyristors, Topology, Torque, Windings, 12-pulse thyristor rectifiers, Fast-response exciters, active rectification, brushless exciters, hybrid-mode operation, multiphase machines, outer-pole PM machines, rotating exciters, synchronous generators
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-328391 (URN)10.1109/TIE.2017.2726963 (DOI)000418415200002 ()
Available from: 2017-08-22 Created: 2017-08-22 Last updated: 2018-01-25Bibliographically approved
Perez-Loya, J. J., Abrahamsson, J., Evestedt, F. & Lundin, U. (2018). Demonstration of Synchronous Motor Start by Rotor Polarity Inversion. IEEE transactions on industrial electronics (1982. Print), 65(10), 8271-8273
Open this publication in new window or tab >>Demonstration of Synchronous Motor Start by Rotor Polarity Inversion
2018 (English)In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 65, no 10, p. 8271-8273Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2018
Keywords
Magnetic fields, starting, synchronous motors
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-362093 (URN)10.1109/TIE.2017.2784342 (DOI)000441990000012 ()
Funder
StandUpSweGRIDS - Swedish Centre for Smart Grids and Energy Storage
Available from: 2018-10-01 Created: 2018-10-01 Last updated: 2018-10-09Bibliographically approved
Yang, W., Norrlund, P., Chung, C. Y., Yang, J. & Lundin, U. (2018). Eigen-analysis of hydraulic-mechanical-electrical coupling mechanism for small signal stability of hydropower plant. Renewable energy, 115, 1014-1025
Open this publication in new window or tab >>Eigen-analysis of hydraulic-mechanical-electrical coupling mechanism for small signal stability of hydropower plant
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2018 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 115, p. 1014-1025Article in journal (Refereed) Published
Abstract [en]

Hydropower shoulders important responsibility for regulation and control of power systems with intermittent renewable energy sources. The quality of regulation required for hydropower units has been increasing, and the interaction between hydropower plants (HPPs) and power systems is of great importance. This work aims to conduct a fundamental study on hydraulic-mechanical-electrical coupling mechanism for small signal stability of HPPs. The main focus is the impact of hydraulic-mechanical factors on the local mode oscillation in a Single-Machine-Infinite-Bus system. A twelfth-order state matrix is established for theoretical eigen-analysis as the core approach. Meanwhile, a simulation model based on Simulink/SimPowerSystems is built for validation. The influencing mechanisms of water column elasticity, governor mechanical component, and water inertia are studied under different control modes of the turbine governor. The results show considerable influence from hydraulic-mechanical factors, and the effect of turbine governor actions is no longer ignorable; also, the damping performance under power system stabilizers can be considerably affected. Insights into interactions among physical quantities in various conditions are obtained as well.

Keywords
Small signal stability, Hydropower plant, Turbine governor, Eigenvalue, Power system stabilizer
National Category
Energy Engineering
Identifiers
urn:nbn:se:uu:diva-340668 (URN)10.1016/j.renene.2017.08.005 (DOI)000413615500092 ()
Available from: 2018-02-05 Created: 2018-02-05 Last updated: 2018-02-05Bibliographically approved
Pérez-Loya, J. J., Abrahamsson, J. & Lundin, U. (2018). Electromagnetic losses in synchronous machines during active compensation of unbalanced magnetic pull. IEEE transactions on industrial electronics (1982. Print), 66(1), 124-131
Open this publication in new window or tab >>Electromagnetic losses in synchronous machines during active compensation of unbalanced magnetic pull
2018 (English)In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 66, no 1, p. 124-131Article in journal (Refereed) Published
Abstract [en]

Unbalanced magnetic pull (UMP) is typically caused by rotor or stator shape defects, electrical short circuits, eccentric rotor/stator bores, as well as unreasonable pole-slot combinations. It leads to vibration and increases noise and energy losses of the machine. By actively controlling the magnetic fields and forces that arise between the rotor and stator by regulating the rotor field current of separated pole groups, it is possible to cancel it. In this paper, we measure and calculate the currents induced in the damper bars for a synchronous machine test rig under 20% static eccentricity with and without active compensation of UMP. This is done to validate our finite-element calculations. Afterward, we perform loss calculations for a 74-MVA synchronous generator with and without stator parallel circuits. We find that, with active compensation of UMP for an eccentric machine, the damper bar currents and stator parallel circuit circulating currents can be eliminated and the electromagnetic efficiency of the machine that has a static eccentricity fault increases.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-328080 (URN)10.1109/TIE.2018.2827991 (DOI)000443894700012 ()
Funder
StandUp
Note

Title in dissertation reference list: Electromagnetic losses in synchronous machines during active compensation of unbalanced magnetic pull due to static eccentricity

Available from: 2017-08-16 Created: 2017-08-16 Last updated: 2018-11-13Bibliographically approved
Yang, W., Sundqvist, P., Lidenholm, J., Yang, J. & Lundin, U. (2018). Hydraulic damping mechanism of low frequency oscillations in power systems: Quantitative analysis using a nonlinear model of hydropower plants. Applied Energy, 212, 1138-1152
Open this publication in new window or tab >>Hydraulic damping mechanism of low frequency oscillations in power systems: Quantitative analysis using a nonlinear model of hydropower plants
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2018 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 212, p. 1138-1152Article in journal (Refereed) Published
Abstract [en]

As power systems grow reliant on an increasing mix of intermittent renewables, hydropower units are being called upon to provide more aggressive power-frequency control. This dynamic is enlarging the significance of interaction between hydraulic and electrical subsystems in hydropower plants (HPPs). The influence from HPPs on power system stability is of great importance, especially for hydro-dominant power systems like the Nordic power system and the China Southern Power Grid. This paper aims to quantify and reveal the influencing mechanism of the hydraulic damping of low frequency oscillations in power systems. An equivalent hydraulic turbine damping coefficient is introduced, and a nonlinear HPP model that combines electrical subsystems with a refined hydraulic-mechanical subsystem is established and verified. A novel quantifying methodology is proposed through simulations by two different models based on case studies on a Swedish HPP. Then, the quantification results of the damping coefficient are presented and the influencing mechanism behind is revealed, by studying three representative factors from the hydraulic-mechanical system: the delay in turbine governor systems, governor parameter and penstock length. Observations and discussions of on-site measurements are included to support the analysis. The results show that the damping effect from hydraulic turbines can be considerable. Based on the limited cases in the HPP, the damping coefficient can vary from + 3.0 to -2.3, while previously the contribution has been unclear and normally assumed to be positive. The phase shift in the mechanical power response with respect to the rotational speed deviation is an important reason for the different damping performance. Furthermore, the effect and significance of implementing the damping coefficient on cases with power system stabilizer (PSS) are demonstrated.

Place, publisher, year, edition, pages
ELSEVIER SCI LTD, 2018
Keywords
Hydraulic damping, Hydro-dominant power systems, Rotor angle stability, Low frequency oscillation, Nonlinear model, Numerical simulation
National Category
Environmental Engineering
Identifiers
urn:nbn:se:uu:diva-348101 (URN)10.1016/j.apenergy.2018.01.002 (DOI)000425200700085 ()
Available from: 2018-04-11 Created: 2018-04-11 Last updated: 2018-04-11Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-9412-4383

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