Overview of Three-Stage Power Converter Topologies for Medium Frequency-based Railway Vehicle Traction Systems

With new developments in power electronics and semiconductor devices, there has been an increasing interest in the adoption of power electronic traction transformer (PETT) topologies in railways, mainly for the purpose of mass and volume reduction against conventional topologies. Apart from traction transformers, examples include isolation circuits for on-board auxiliary power units (APU) and even 750 VD C, 110 VD C and lower voltage (e.g., 72 VD C) battery chargers. Special attention has been given to the more mature technology of three-stage (ac–dc–MFac–dc) configurations with intermediate medium frequency ac (MFac) links. In contrast to onventional architectures, it becomes difficult to select a suitable multistage topology of power electronics for the design of complex traction systems with advanced requirements. The power electronics utilized in different configurations have a significant effect on performance, efficiency, power quality (harmonics and stability), and cost indicators for the whole system, making the selection and design process more complex. The objective of this paper is to provide a clear overview of proposed topologies with special emphasis on the power electronic architectures utilized in three-stage PETT systems particularly for railway traction systems and on-board APUs. With regards to the listed range of possible architectures provided to the reader, key characteristics, such as total semiconductor (switches and diodes) count numbers per module per phase, input/output voltage levels, operating frequencies, and the most commonly used resonant networks, are summarized and discussed