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Comparison of Thyristor Rectifier Configurations for a Six-Phase Rotating Brushless Outer Pole PM Exciter
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.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.ORCID iD: 0000-0003-4265-6545
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
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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.

Place, publisher, year, edition, pages
2018. Vol. 65, no 2, p. 968-976
Keywords [en]
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: urn:nbn:se:uu:diva-328391DOI: 10.1109/TIE.2017.2726963ISI: 000418415200002OAI: oai:DiVA.org:uu-328391DiVA, id: diva2:1135278
Available from: 2017-08-22 Created: 2017-08-22 Last updated: 2018-01-25Bibliographically approved
In thesis
1. Analysis and control of magnetic forces in synchronous machines
Open this publication in new window or tab >>Analysis and control of magnetic forces in synchronous machines
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In a synchronous machine, radial, tangential, and axial forces are generated. In this thesis, three different technologies to control them are proposed. The first one, involves the utilization of the radial forces that arise between the rotor and the stator. This is achieved by segmenting the rotor field winding into groups of poles and controlling their corresponding magnetization individually. This technology is particularly useful to achieve magnetic balance and to create controllable radial forces. The second technology, involves the control of the rotor field in order to influence the tangential forces that produce torque. This is achieved by inverting the rotor field winding polarity with respect to the stator field. With this technique, breaking and accelerating torques can be created. It is particularly useful to start a synchronous machine. Finally, the application of axial forces with a magnetic thrust bearing is discussed. The main benefits of this technology are higher efficiency and increased reliability.

The work presented in this thesis was carried out within the Division of Electricity in the Department of Engineering Sciences at Uppsala University. It is based on original research supported by analytical calculations, computational simulations and extensive experimental work.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. p. 84
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1542
Keywords
eccentricity, electromagnetics, electromagnetic forces, excitation, magnetic fields, magnetic forces, magnetic thrust bearing, rotor drive, split rotor, starting, synchronous generators, synchronous machines, synchronous motors, unbalanced magnetic pull
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-328086 (URN)978-91-513-0036-8 (ISBN)
Public defence
2017-10-06, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2017-09-13 Created: 2017-08-16 Last updated: 2017-10-17
2. Improving the functionality of synchronous machines using power electronics
Open this publication in new window or tab >>Improving the functionality of synchronous machines using power electronics
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

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

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

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

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

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017
Series
UURIE / Uppsala University, Department of Engineering Sciences, ISSN 0349-8352 ; 352-17L
Keywords
Power electronics, Synchronous machines, Excitation systems, Magnetic thrust bearing, Starting synchronous machines, Split rotor, Rotating electronics, Magnetic fields, Measurement systems, Unbalanced magnetic pull, Harmonics
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-333940 (URN)
Presentation
2017-12-18, Häggsalen (Å10132), Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2018-01-08 Created: 2017-11-20 Last updated: 2018-01-08Bibliographically approved
3. A New Paradigm for Large Brushless Hydrogenerators: Advantages Beyond the Static System
Open this publication in new window or tab >>A New Paradigm for Large Brushless Hydrogenerators: Advantages Beyond the Static System
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The grid code, FIKS, from the Norwegian transmission system operator (TSO), Statnett, states that synchronous generators > 25MVA, must have a static excitation system. However, an improved brushless excitation system is in operation on some commercial power plants (36MVA, 93.75rpm & 52MVA, 166.67rpm) with grid-assisting performance beyond the conventional static system. The convenional diode bridge is replaced with a remote-controlled thyristor bridge on the shaft. If wireless communication is not allowed, a control signal through brushes should be employed instead. The thesis explores the expected new era for large brushless hydrogenerators. The proposed brushless system have benefits of reduced regular maintenance due to elimination of brushes and reduced unscheduled maintenance due to redundancy; causing a redused cost-of-energy. A six-phase exciter design with a hybrid-mode thyristor bridge interface leads to improved fault-tolerance, better controllability, minimized torque pulsations and reduced armature currents of the exciter. Excitation boosting (EB) capability is included in the brushless system without additional components or circuitry, contrary to the static excitation system. The brushless excitation system is made insensitive to voltage dips in the interconnected grid, causing improved fault ride-through (FRT) capability and power system stabilizer (PSS) actions. 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. p. 93
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1491
Keywords
Brushless exciters, Rotating exciters, Permanent Magnet Machines, Synchronous Generator Excitation, Thyristor Rectifiers, Chopper Rectifiers
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-317780 (URN)978-91-554-9859-7 (ISBN)
Public defence
2017-05-10, Häggsalen, Ångströmlaboratoriet, Polacksbacken, Lägerhyddsvägen 2, Uppsala, 13:00 (English)
Opponent
Supervisors
Available from: 2017-04-19 Created: 2017-03-17 Last updated: 2018-02-15

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Kristiansen Nøland, JonasEvestedt, FredrikPérez-Loya, Jesús JoséAbrahamsson, JohanLundin, Urban

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