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A New Paradigm for Large Brushless Hydrogenerators: Advantages Beyond the Static System
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Hydropower)
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 [en]
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: urn:nbn:se:uu:diva-317780ISBN: 978-91-554-9859-7 (print)OAI: oai:DiVA.org:uu-317780DiVA, id: diva2:1082796
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
List of papers
1. Design and Characterization of a Rotating Brushless Outer Pole PM Exciter for a Synchronous Generator
Open this publication in new window or tab >>Design and Characterization of a Rotating Brushless Outer Pole PM Exciter for a Synchronous Generator
Show others...
2017 (English)In: IEEE transactions on industry applications, ISSN 0093-9994, E-ISSN 1939-9367, Vol. 53, no 3, p. 2016-2027Article in journal (Refereed) Published
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.

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-315594 (URN)10.1109/TIA.2017.2669890 (DOI)000402062600031 ()
Available from: 2017-02-15 Created: 2017-02-15 Last updated: 2018-09-17Bibliographically approved
2. Comparison of Thyristor-Controlled Rectification Topologies for a Six-Phase Rotating Brushless Permanent Magnet Exciter
Open this publication in new window or tab >>Comparison of Thyristor-Controlled Rectification Topologies for a Six-Phase Rotating Brushless Permanent Magnet Exciter
2016 (English)In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 31, no 1, p. 314-322Article in journal (Refereed) Published
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.

Keywords
brushless exciters, rotating exciters, controlled excitation, permanent magnet machines, synchronous generators, voltage stabiliy
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-269214 (URN)10.1109/TEC.2015.2480884 (DOI)000372024100030 ()
Available from: 2015-12-15 Created: 2015-12-15 Last updated: 2017-12-01Bibliographically approved
3. Testing of Active Rectification Topologies on a Six-Phase Rotating Brushless Outer Pole PM Exciter
Open this publication in new window or tab >>Testing of Active Rectification Topologies on a Six-Phase Rotating Brushless Outer Pole PM Exciter
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2018 (English)In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 33, no 1, p. 59-67Article in journal (Refereed) Published
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.

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-328396 (URN)10.1109/TEC.2017.2746559 (DOI)000425623700007 ()
Available from: 2017-08-22 Created: 2017-08-22 Last updated: 2018-04-25Bibliographically approved
4. Comparison of Thyristor Rectifier Configurations for a Six-Phase Rotating Brushless Outer Pole PM Exciter
Open this publication in new window or tab >>Comparison of Thyristor Rectifier Configurations for a Six-Phase Rotating Brushless Outer Pole PM Exciter
Show others...
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
5. Failure-Modes Identification and Redundant Postfault Operation of Rotating Thyristor Rectifiers on Brushless Dual-Star Exciters
Open this publication in new window or tab >>Failure-Modes Identification and Redundant Postfault Operation of Rotating Thyristor Rectifiers on Brushless Dual-Star Exciters
2018 (English)In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. PP, no 99, p. 1-10Article in journal (Refereed) Epub ahead of print
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.

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-317775 (URN)10.1109/TIE.2018.2833044 (DOI)
Available from: 2017-03-17 Created: 2017-03-17 Last updated: 2018-05-04
6. Design and characterization of a rotating brushless PM exciter for a synchronous generator test setup
Open this publication in new window or tab >>Design and characterization of a rotating brushless PM exciter for a synchronous generator test setup
Show others...
2016 (English)In: Design and characterization of a rotating brushless PM exciter for a synchronous generator test setup / [ed] IEEE Xplore, 2016, p. 259-265Conference paper, Published 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.

Keywords
Brushless exciters, rotating exciters, permanent magnet machines, machine design, voltage measurement
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-292798 (URN)10.1109/ICELMACH.2016.7732536 (DOI)000390884900037 ()9781509025381 (ISBN)
Conference
International Conference on Electrical Machines 2016 (ICEM'16), Lausanne, SWITZERLAND, SEP 04-07, 2016
Available from: 2016-05-09 Created: 2016-05-09 Last updated: 2017-11-20Bibliographically approved
7. Evaluation of different power electronic interfaces for control of a rotating brushless PM exciter
Open this publication in new window or tab >>Evaluation of different power electronic interfaces for control of a rotating brushless PM exciter
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2016 (English)In: Evaluation of different power electronic interfaces for control of a rotating brushless PM exciter / [ed] IEEE Xplore, 2016Conference paper, Published paper (Refereed)
Abstract [en]

This 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 in 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.

Keywords
power electronic interfaces
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-292801 (URN)10.1109/IECON.2016.7794011 (DOI)978-1-5090-3474-1 (ISBN)
Conference
Annual Conference on of the IEEE Industrial Electronics Society 2016 (IECON'16)
Available from: 2016-05-09 Created: 2016-05-09 Last updated: 2017-03-17
8. Step time response evaluation of different synchronous generator excitation systems
Open this publication in new window or tab >>Step time response evaluation of different synchronous generator excitation systems
2016 (English)In: Step time response evaluation of different synchronous generator excitation systems, IEEE Xplore, 2016Conference paper, Published paper (Refereed)
Abstract [en]

A fast step response of an excitation system is critical for a synchronous generator in order to maintain stability under disturbances in the interconnected power grid. This is the main reason that the static excitation system has been preferred for large synchronous generators. Some transmission system operators even have requirements that the excitation system should be static for synchronous generators above a certain size. The requirement is set in order to fulfill a certain goal for the step time response. As technology progresses forward, the static excitation system will not any longer be the only option for a fast controllable excitation system. New brushless rotating excitation systems, with wireless control interfaces, can be even faster than the static excitation system. They also reduce the need of maintenance of the synchronous generator. With permanent magnet exciters, the excitation system can be independent from the grid, maintaining the excitation response under voltage dips in the power grid. This paper evaluates the dynamic performance of the static excitation system compared with different types of brushless rotating excitation systems.

Place, publisher, year, edition, pages
IEEE Xplore: , 2016
Keywords
synchronous generator modelling
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-292792 (URN)10.1109/ENERGYCON.2016.7513956 (DOI)000390822900086 ()9781467384636 (ISBN)
Conference
IEEE International Energy Conference 2016 (ENERGYCON'16)
Available from: 2016-05-09 Created: 2016-05-09 Last updated: 2017-03-17Bibliographically approved
9. Børsteløs magnetisering gir bedre nettstabilitet
Open this publication in new window or tab >>Børsteløs magnetisering gir bedre nettstabilitet
2016 (Norwegian)In: Energiteknikk : fagbladet for energibransjen, no 6, p. 50-51Article in journal (Other (popular science, discussion, etc.)) Published
Abstract [no]

Børsteløse magne seringsutrustninger kom på 1950-tallet etter er utviklingen av kompakte høyeffekts silisium- dioder. I prinsippet bygde man en forvrengt synkronmaskin og puttet den på samme akslingen som synkrongeneratoren. Feltviklingen på denne maskinen lå i stator, mens den trefasede armaturviklingen ble satt i rotor. En roterende diodebro paå akslingen knyttet magnetiseringsmaskinen sammen med generatorens feltvikling.Den trege responsen l den børsteløse magnetiseringsutrustningen er hovedårsaken l at den ikke slo igjennom tross redusert vedlikehold av magnetiseringssystemet. Paå 1980-tallet forsøkte man å bygge en magnetiseringsmaskin med lave induktanser for å gjøre responsen like rask som statiske magnetiseringsutrustninger. Denne artikkelen viser til at den roterende diodebroen kan byttes ut med en thyristorbro på akslingen, og dermed forbedre stegresponsen. I tillegg har systemet fordeler i forhold til magnetiserinssystemets evne til å motstå spenningsdipper på nett, derav FRT-kapabilitet. En sammenligning med statisk system blir gjort.

Place, publisher, year, edition, pages
ElektoMedia AS, 2016
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-317779 (URN)
Available from: 2017-03-17 Created: 2017-03-17 Last updated: 2017-03-23Bibliographically approved

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Nøland, Jonas Kristiansen

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