Optimal sizing of a power electronic traction transformer for railway applications

Abstract

Many works are dedicated to power electronic transformers in order to replace line frequency transformers. These new converters offer many degrees of freedom to the designer (switching frequency, magnetic material, rated voltage for switches. . . ). This paper presents a methodology to optimize the sizing of such power converters in order to compare different topologies for a given application. The proposed procedure maximises the efficiency of the converter under a limited volume. In this paper, the methodology is applied to compare different topologies of power electronic traction transformers (PETT) for railway applications. The considered case is a 2 MW converter supplied by a 25 kV-50 Hz catenary. The procedure is illustrated in simulation on a converter with 3.3 kV SiC switches. The best obtained efficiency is 98.9 % with 23 medium frequency transformers (MFT) of 28.6 L each.

SiC-Based Power Electronic Traction Transformer (PETT) for 3 kV DC Rail Traction

“…In order to obtain noiseless operation of MV drives, multi-level topologies are used with the use of low-voltage (1.2 kV or 1.7 kV) SiC transistors. Among others, power electronic traction transformers (PETTs), built with power electronic building blocks (PEBB) with built-in input/output isolation, realized by small size and high power density medium frequency transformers (MFT) are of particular interest [13][14][15][16][17][18][19].…”

“…So far, the primary purpose of SiC-based PETTs were primarily traction drives powered from the AC lines: 15 kV/16.7 Hz [13,14,18,19] and 25 kV/50 Hz [15][16][17]. AC powered locomotives and EMUs have a complex and voluminous conversion chain including a step-down transformer, rectifier, low-frequency filter and traction inverter.…”

“…Strictly speaking, the AC PETT replaces the system of an LFT and an active rectifier and the AC PETT topology does not include a propulsion inverter, which stays the same as in a classical propulsion system and is connected to DC output terminals of the PETT [3,[13][14][15][16][17][18][19].…”

“…However, the concept was verified only on a small scale test rig. The works [15] and [16] present the method of optimal sizing of 25 kV/50 Hz-type PETTs using 3.3 kV SiC MOSFETs that leads to the best efficiency at rated power in a given volume. The authors emphasize that the efficiency cannot be the only parameter to make a clear choice of an isolated DC-DC converter included in a PETT.…”

Effective Permeability of Multi Air Gap Ferrite Core 3-Phase Medium Frequency Transformer in Isolated DC-DC Converters

“…The ferrite also offers low cost in terms of material and transformer assembly. In [32], the ferrite core MFT was considered for an optimized dc-dc converter operating at a few kHz. Finally, the ferrite seems as a good candidate for the short term industrialization of the high power three-phase MFT.…”