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Design Considerations for a Medium Frequency Transformer in a Line Side Power Conversion System
KTH, Superseded Departments, Electrical Systems. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
KTH, Superseded Departments, Electrical Systems.ORCID iD: 0000-0002-8565-4753
KTH, Superseded Departments, Electrical Systems. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.ORCID iD: 0000-0001-7330-146X
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. 704-710 p.
Series
IEEE power electronics specialists conference records, ISSN 0275-9306
Keyword [en]
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: urn:nbn:se:kth:diva-10422DOI: 10.1109/PESC.2004.1355834ISI: 000224587600113Scopus ID: 2-s2.0-8744291981ISBN: 0-7803-8399-0 (print)OAI: oai:DiVA.org:kth-10422DiVA: diva2:217092
Note
QC 20100723Available from: 2009-05-13 Created: 2009-05-13 Last updated: 2010-12-06Bibliographically approved
In thesis
1. On Design of a Compact Primary Switched Conversion System for Electric Railway Propulsion
Open this publication in new window or tab >>On Design of a Compact Primary Switched Conversion System for Electric Railway Propulsion
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
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:nbn:se:kth:diva-10428 (URN)978-91-7415-327-9 (ISBN)
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

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Norrga, StaffanÖstlund, Stefan

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