Current Distortion Evaluation in Traction 4Q Constant Switching Frequency Converters

The paper deals with the power quality analysis of interlaced four quadrant (4Q) converters with constant switching frequency. These are in fact the input stages of the locomotives and high speed trains supplied by 25 kV, 50 Hz and 15 kV, 16.7 Hz lines. Due to the high power needed for the trains circulation, the 4Q converter can absorb distorted currents, whose harmonic content can affect the signaling systems and communication devices. The presence of more converters gives the opportunity, using dedicated commutation strategy, to interlace them in order to reduce the harmonic content in the absorbed current. In the paper a suitable model of more 4Q converters is developed. The control logic implemented in the model allows the evaluation of the harmonic contribution of both single converter and the interlaced configuration. The analysis is carried out through electromagnetic transient simulations.