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    New Configuration of Traction Converter WithMedium-Frequency Transformer Using

    Matrix ConvertersPavel Drbek, Member, IEEE, Zdenek Peroutka, Member, IEEE, Martin Pittermann, and Marek Cdl

    AbstractThis paper presents a new configuration of a maintraction converter with a medium-frequency transformer (MFT)using matrix converters intended for locomotives and partic-ularly for suburban units supplied by a 25-kV/50-Hz and/or15-kV/16.7-Hz ac electrification system. Single-phase matrix con-verters are employed in the primary medium-voltage converterwhich is directly connected to the ac trolley line. The output of theprimary ac/ac converter supplies the primary side of the MFT. Theproposed MFT-based topology of the traction converter replacesthe bulky main line transformer found on board railway vehicles.Particularly in countries with a catenary of 15 kV/16.7 Hz, verylow catenary frequency results in huge and heavy traction trans-formers. The developed topology is a power electronics solutionthat considerably reduces weight and losses in a traction propul-sion system. The proposed converter configuration with cascadedmatrix converters on the primary side of the MFT presents a newresearch direction in the field of traction converters with MFTs.This paper describes in detail the proposed power circuit andthe control of the traction converter. The behavior of the tractionconverter configuration has been analyzed using simulations andexperimental tests carried out on a developed low-voltage labora-tory prototype of a traction converter with a rated power of 4 kVA.Based on extensive simulation and experimental study, this paperreviews the benefits, drawbacks, and constraints of the developedtraction converter configuration.

    Index TermsACAC converters, locomotive, matrix con-verters, medium-voltage converters, power conversion, railtransportation.


    THIS RESEARCH has been motivated by the industrialdemand for a design of a traction converter with amedium-frequency transformer (MFT) using matrix convertersto replace the bulky main line transformer found on boardrailway vehicles.

    Manuscript received December 6, 2010; revised March 1, 2011; acceptedMarch 15, 2011. Date of publication April 5, 2011; date of current versionSeptember 7, 2011. This work was supported by the European RegionalDevelopment Fund and Ministry of Education, Youth and Sports of the CzechRepublic, under Project CZ.1.05/2.1.00/03.0094: Regional Innovation Centrefor Electrical Engineering, and in part by the Czech Science Foundation underProject GACR 102/09/1164.

    P. Drbek, M. Pittermann, and M. Cdl are with the Department of Electro-mechanics and Power Electronics, University of West Bohemia, 306 14 Pilsen,Czech Republic (e-mail:;;

    Z. Peroutka is with the Regional Innovation Centre for Electrical Engi-neering, University of West Bohemia, 306 14 Pilsen, Czech Republic (

    Color versions of one or more of the figures in this paper are available onlineat

    Digital Object Identifier 10.1109/TIE.2011.2138114

    The recent trend in the research of new traction convertertopologies for multisystem locomotives, trains, suburban units,and vehicles supplied by ac electrification systems is stronglyoriented toward the reduction of the weight and dimensions ofa new generation of electrical equipment used in these vehicles[1][11]. The investigated traction converter configurations areoften inspired by known topologies from switching powersupplies, which are however operated at dramatically differentpower levels. One of the perspective configurations of the newtraction converters is a topology employing an MFT. The ben-efits of medium- or high-frequency transformers in comparisonwith conventional transformers are well known, e.g., in theaerospace industry [12][14].

    The use of an MFT in the main traction converter requires acomplex reworking of its configuration. The input part of a newtraction converter is composed of a primary medium-voltagefrequency converter which is directly connected to the actrolley line (without an input transformer) and supplies theprimary winding of the MFT at a frequency significantly higherthan the frequency of a catenary. The primary medium-voltageconverter is, in general, a major research challenge. Theexisting solutions published in the literature mostly use indirectfrequency converters at the primary side of the MFT [3],[10], [11]. A further interesting configuration of the primaryconverter represents the ac/ac modular multilevel converter(M2LC) topology introduced, e.g., in [4], [9], and [15][18].

    The previously mentioned solutions all have various disad-vantages, e.g., indirect frequency converters demand bigger ca-pacitors in the dc bus and the M2LC topology contains a highernumber of switching devices in comparison to the indirect ordirect converter topology. One power cell at the primary trans-formers side of the M2LC topology has four arms, and eacharm includes four insulated-gate bipolar transistors (IGBTs),i.e., 16 IGBTs per cell, whereas either the direct or indirecttopology contains only eight IGBTs per primary power cell.

    Many papers are oriented toward applications with three-phase matrix converters [19][29] as a replacement for standardthree-phase indirect frequency converters. The use of matrixconverters at the primary (medium-voltage) side of the MFTis a new research direction which is discussed in this paper.

    A similar idea, i.e., the primary matrix converter, was alsopresented in [30]. Hugo et al. [30] use a separate MFT for eachconverter power cell. In contrast, our converter uses multipleprimary windings of the MFT (see Fig. 3) which secures naturalvoltage balancing of the input filters on the primary powercells. Moreover, this paper also presents new converter controlmethods.

    0278-0046/$26.00 2011 IEEE


    Fig. 1. Configuration of a conventional traction vehicle fed from the acelectrification system with a heavy low-frequency transformer at input.

    Fig. 2. Configuration of a new traction converter with the MFT.

    The aim of this paper is to examine the benefits and draw-backs of the traction converter with single-phase matrix con-verters at the primary side of the MFT.

    This paper is organized as follows. First, the proposedconfiguration of the new traction converter with the MFTemploying matrix converters at the primary (medium-voltage)side of the transformer is presented. Second, the developedcontrol of both primary and secondary converters is described.Third, the behavior of the designed small-scale prototype of thetraction converter is analyzed by simulations and experimentsunder steady-state and selected transient conditions. Finally,the benefits, drawbacks, and constraints of the proposed newconfiguration of the traction converter are presented in the finalsection of this paper.


    In the conventional topology (see Fig. 1), the traction con-verter uses a heavy low-frequency transformer at its input.There is a huge problem with the input transformer, particu-larly with the ac 15-kV/16.7-Hz electrification system, whereultralow catenary frequency results in a bulky transformer.As described in the previous section, one of the prospectivemethods of overcoming the aforementioned constraints is anew traction converter using an MFT. The configuration of thetraction converter with the MFT is shown in Fig. 2. The tractionconverter consists of an input filter [medium-voltage input filter(MVF)], a primary medium-voltage converter (MVC) supply-ing an MFT, and the main traction drive converter (TDC).

    Fig. 3. Proposed configuration of a new traction converter with an MFT usingcascaded single-phase matrix converters on the primary transformer side.

    The input converter (MVC presented in Fig. 3 and describedin Section III) regulates the input line voltage to the appropriatewaveform for the MFT (in general, it increases the frequency atthe MFT).

    The MFT secures galvanic insulation between the input andoutput and adjusts the output voltage level.

    The output traction converter (TDC) connected at the sec-ondary side of the MFT supplies the traction motors.

    In this paper, we propose a new matrix converter-basedconfiguration of the primary medium-voltage converter (MVC)which is explained in detail in Section III. The output tractiondrive converter is based on an indirect frequency converterconsisting of a voltage-source active rectifier and a voltagesource inverter.


    Fig. 3 shows the proposed configuration of a new tractionconverter with an MFT. We have used the MFT with several pri-mary windings and only one secondary winding. The primarywindings are supplied by the input medium-voltage converterwhich, in our case, is composed of cascaded cells (each cellrepresents one frequency converter). Each cell supplies oneprimary winding of the MFT. The particular cells are basedon a single-phase matrix converter. The power circuit for theproposed single-phase matrix converter must, of course, becompleted on the catenary side by an input medium-voltage fil-ter (reactor LF and capacitor CF ). The single secondary wind-ing of the MFT supplies a single-phase voltage-source activerectifier of the main traction drive converter (TDC). The filterwith a capacitor is situated at the input of the matrix converter,and the inductive load (winding of the transformer) is connectedat its output. These facts have to be taken into account bythe matrix converter control


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