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On Design of a Compact Primary Switched Conversion System for Electric Railway Propulsion
KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, a compact and light primary switched conversion system for AC-fed railway propulsion is investigated. It is characterized by soft switching of all converter stages and a source commutated primary converter comprising series connected valves. Both weight and volume of the conversion system are reduced significantly compared to a conventional system with a low frequency transformer.

The conversion system is made up of N isolated AC/DC conversion cells, each comprising a cycloconverter and a voltage source converter (VSC) coupled by a medium frequency transformer. The cells are series connected on the AC side and connected to a common DC-link. Thus, 2N+1 voltage levels can be synthesized at the AC terminal and the voltage stress on the transformer and line filter is reduced compared to a one cell solution. Series connection of semiconductor valves allows independent choice of blocking voltage and number of converter cells. Choosing two converter cells is an attractive compromise. Five level output reduces the harmonic distortion and simplify transformer and line filter design while keeping the complexity of the conversion system low.

The mutually commutated converter (MCC) allows a transformer frequency in the range of 4 to 8 kHz without derating the line side converter due to zero voltage switching of the VSC. Modern magnetic materials, like high silicon steel, amorphous and noncrystalline materials allow design of the transformer with high efficiency at elevated frequencies.

In a 15 kV system, the peak voltage at the catenary is typically beyond 32 kV which is far beyond the voltage capability of currently available semiconductors. Therefore, several semiconductors are connected in series. Favourable commutation conditions and a new gate drive arrangement allow snubberless commutation of the primary converter stage. Thus, the primary converter can be highly integrated, reducing both weight and volume. The conversion system can be placed on the roof or in the underframe without compromising efficiency or vehicle performance.

The feasibility of the conversion concept has been demonstrated by means of a down-scaled prototype. Snubberless commutation of series connected valves is demonstrated.

Place, publisher, year, edition, pages
Stockholm: KTH , 2009. , viii, 75 p.
Series
Trita-EE, ISSN 1653-5146 ; 2009 : 29
Keyword [en]
Isolated AC/DC converter, Mutual commutation, Soft Switching, Cyclo converter, Medium-Frequency Transformer, Electric Railway Propulsion
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-10428ISBN: 978-91-7415-327-9 (print)OAI: oai:DiVA.org:kth-10428DiVA: diva2:217187
Public defence
2009-06-05, D3, Lindstedtvägen 5, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100723Available from: 2009-05-18 Created: 2009-05-13 Last updated: 2010-07-23Bibliographically approved
List of papers
1. Design Considerations for a Medium Frequency Transformer in a Line Side Power Conversion System
Open this publication in new window or tab >>Design Considerations for a Medium Frequency Transformer in a Line Side Power Conversion System
2004 (English)In: Proceedings of the 35th Annual IEEE Power Electronics Specialist Conference, PESC 2004, IEEE , 2004, 704-710 p.Conference paper, Published paper (Refereed)
Abstract [en]

Design considerations are presented for a medium frequency transformer in a line side power conversion system for electric railway traction. The system employs soft commutation in order to reduce switching losses and allow for high operating frequency of the transformer. Two different designs are evaluated; The first one is dry insulated and the second one is liquid-immersed. Calculations indicate that a 1 MVA transformer operating at 4 kHz could be realized with an active weight of below 150 kg for both dry and liquid-immersed transformer concepts. The transformers are modeled magnetically, electrically and thermally, and a geometric optimization procedure based on a cost function is applied to achieve an optimum design.

Place, publisher, year, edition, pages
IEEE, 2004
Series
IEEE power electronics specialists conference records, ISSN 0275-9306
Keyword
Boundary layers; Dielectric materials; Electric commutation; Electric insulation; Electric railroads; Electric traction; Gravitational effects; Heat flux; Heat transfer coefficients; Power converters; Switching
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Järnvägsgruppen - Elsystem
Identifiers
urn:nbn:se:kth:diva-10422 (URN)10.1109/PESC.2004.1355834 (DOI)000224587600113 ()2-s2.0-8744291981 (Scopus ID)0-7803-8399-0 (ISBN)
Note
QC 20100723Available from: 2009-05-13 Created: 2009-05-13 Last updated: 2010-12-06Bibliographically approved
2. Switching Frequency Limit for Soft-Switching MF Transformer System for AC-fed Traction
Open this publication in new window or tab >>Switching Frequency Limit for Soft-Switching MF Transformer System for AC-fed Traction
2005 (English)In: Proceesings of the 36th Annual IEEE Power Electronics Specialist Conference, PESC 2005, IEEE , 2005, 1678-1684 p.Conference paper, Published paper (Refereed)
Abstract [en]

The migration to line side power conversion topologies comprising a medium frequency transformer in AC-fed propulsion systems may reduce size and weight of the conversion system. The switching frequency is a crucial factor affecting the viability of such a conversion system. An increased switching frequency of a mutually commutated conversion system comprising a medium frequency transformer employing soft switching is verified by single pulse measurements. A test bench to characterize standard IGBT modules under soft switching has been build and loss measurements on a 3.3 kV IGBT module are presented for hard and soft switching. A loss model of the investigated topology is developed and the maximum switching frequency for a converter equipped with the investigated module is estimated for hard and soft switching.

Place, publisher, year, edition, pages
IEEE, 2005
Series
IEEE POWER ELECTRONICS SPECIALISTS CONFERENCE RECORDS, ISSN 0275-9306
Keyword
Analog to digital conversion; Electric losses; Electric network topology; Electric traction; Electric transformers
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Järnvägsgruppen - Elsystem
Identifiers
urn:nbn:se:kth:diva-10423 (URN)10.1109/PESC.2005.1581856 (DOI)000237036501109 ()2-s2.0-33847758986 (Scopus ID)0-7803-9033-4 (ISBN)
Conference
36th Annual IEEE Power Electronic Specialists Conference (PESC 05). Recife, BRAZIL. JUN 12-16, 2005
Note

QC 20100723

Available from: 2009-05-13 Created: 2009-05-13 Last updated: 2016-06-20Bibliographically approved
3. Harmonic Mitigation in Single Phase Mutually Commutated Converter Systems
Open this publication in new window or tab >>Harmonic Mitigation in Single Phase Mutually Commutated Converter Systems
2006 (English)In: Proceedings of the 37th Annual IEEE Power Electronics Specialists Conference, PESC 2006, NEW YORK, NY: IEEE , 2006, 1542-1548 p.Conference paper, Published paper (Refereed)
Abstract [en]

An AC/DC converter comprising a cycloconverter and a capacitively snubbered voltage source converter (VSC), coupled by a medium frequency transformer, offers significant advantages. Bidirectional AC/DC power flow as well as voltage transformation and isolation can be achieved. By mutual commutation of the converters, soft switching can be achieved for all semiconductors, thus, link frequency can be increased, allowing smaller transformer and reduced filter components. However, the mutual commutation scheme imposed by the soft switching requirement puts constraints on the PWM pattern causing low frequency harmonics in certain operating points. It is shown that the low frequency harmonics can be eliminated for all points of operation, both in a single bridge configuration and interlaced configuration, common in AC-fed propulsion. A sub-optimal harmonic mitigation method based on a regularly sampled modulator is proposed. By proper oversampling of the reference waveforms substantial reduction of the low frequency harmonic contents can be achieved. The mitigation method is verified by circuit simulation and the feasibility to propulsion is demonstrated.

Place, publisher, year, edition, pages
NEW YORK, NY: IEEE, 2006
Series
IEEE POWER ELECTRONICS SPECIALISTS CONFERENCE RECORDS, ISSN 0275-9306
Keyword
Electric transformers; Harmonic analysis; Switching
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-10424 (URN)10.1109/PESC.2006.1712205 (DOI)000245402503017 ()2-s2.0-42449148709 (Scopus ID)0-7803-9716-9 (ISBN)
Conference
37th IEEE Power Electronics Specialist Conference (PESC 2006). Cheju Isl, SOUTH KOREA. JUN 18-22, 2006
Note
QC 20100723Available from: 2009-05-13 Created: 2009-05-13 Last updated: 2011-10-07Bibliographically approved
4. Active Snubber Circuit for Source Commutated Converters Utilizing the IGBT in the Linear Region
Open this publication in new window or tab >>Active Snubber Circuit for Source Commutated Converters Utilizing the IGBT in the Linear Region
2008 (English)In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 23, no 5, 2595-2601 p.Article in journal (Refereed) Published
Abstract [en]

This paper describes a gate control method where an IGBT is controlled in its linear region by means of closed loop control in order to regulate the voltage slope during turn-on and to clamp the voltage of an anti-parallel diode in a source commutated converter. Controlling the voltage slope may be necessary in a high voltage converter to avoid emission of EMI or to avoid triggering oscillations which may cause insulation failure. Controlling the switching trajectory without influence from the device characteristics is important where series-connection is necessary to increase the overall blocking voltage. The control method has been verified by means of a prototype.

Place, publisher, year, edition, pages
IEEE, 2008
Keyword
Ac-ac power conversion; Electromagnetic interference; Insulated gate bipolar transistors; Snubbers
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Järnvägsgruppen - Elsystem
Identifiers
urn:nbn:se:kth:diva-10425 (URN)10.1109/TPEL.2008.2002093 (DOI)000261599700038 ()2-s2.0-57349189392 (Scopus ID)
Note

QC 20150624

Available from: 2009-05-13 Created: 2009-05-13 Last updated: 2015-11-11Bibliographically approved
5. Thermal Evaluation of a Medium Frequency Transformer in a Line Sider Conversion System
Open this publication in new window or tab >>Thermal Evaluation of a Medium Frequency Transformer in a Line Sider Conversion System
2009 (English)In: Proceedings of the 13th International European Electronics Conference and Exhibition, EPE '09, IEEE , 2009, 2517-2526 p.Conference paper, Published paper (Refereed)
Abstract [en]

A central part of a medium frequency conversion system is the transformer. A medium frequency transformer for railway propulsion may be stressed beyond 30kV with voltage slopes around 50kV/mu s depending on topology while the geometric dimensions are small. A 170kVA transformer prototype operated at 4 kHz has been developed and tested.

A transient thermal model of the transformer is developed and verified experimentally. The transient thermal behavior is important in propulsion applications where the conversion system is often heavily overloaded. Simulations indicate that the overloading capability of the transformer is comparable to a conventional traction transformer. Experimental results are in good agreement with the model.

Place, publisher, year, edition, pages
IEEE, 2009
Keyword
Transformer, High frequency power converter, Thermal design, Rail vehicle
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Järnvägsgruppen - Elsystem
Identifiers
urn:nbn:se:kth:diva-10426 (URN)000275384101045 ()2-s2.0-72949091735 (Scopus ID)978-1-4244-4432-8 (ISBN)
Conference
2009 13th European Conference on Power Electronics and Applications, EPE '09; Barcelona; 8 September 2009 through 10 September 2009
Note

QC 20110304

Available from: 2009-05-13 Created: 2009-05-13 Last updated: 2014-10-09Bibliographically approved

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