LAUSR

This paper presents an implementation of control algorithms of traction converter topology with medium frequency transformer (MFT) using matrix converters intended for locomotives and particularly for suburban units supplied by a 25 kV/50 Hz and/or 15 kV/16.7 Hz AC overhead line. Traction converter consists of input medium voltage matrix converters directly connected to the overhead line and outputs supply MFTs. The proposed traction converter concept with MFT replaces classical topology based on bulky line traction transformer and significantly reduces size and weight of the traction transformer. This paper describes in detail control algorithms and their implementation of the proposed converter configuration. The converter concept with common MFT using coupled magnetic flux for balancing input capacitor voltages and modular concept with separate power cell and individual MFTs have been discussed. The paper analyses in detail the matrix converter commutation based on standard 4-step commutation with respect to knowledge of input voltage polarity or output current polarity. The control algorithms also keep in touch the minimizing of the MFT magnetic saturation at extremely low switching frequency. The behaviour of the proposed converter power circuit has been analysed by simulations and verified by experimental test on developed low-scale functional prototype with rated power up to 4 kVA.