Power Electronic Transformer-Based Railway Traction Systems: Challenges and Opportunities

In this paper, power electronic transformer (PET)-based railway traction systems are comprehensively reviewed according to the unique application features and requirements. By comparing PET and conventional line frequency transformer (LFT)-based systems, their pros and cons are summarized. By further reviewing all kinds of PET-based designs from the early concepts to the latest ones in the order of their publication dates, the developing trends are highlighted. By synthetically considering the requirements and the state of the art, the key challenges and opportunities are identified and discussed. It shows that although PET-based systems are still developing and far from mature, they are already superior to LFT-based systems in terms of system weight, efficiency, and functionalities especially for 15-kV/16.7-Hz applications. With the advancements on wide bandgap power devices, medium frequency transformers, and converters, PET systems will be even more promising and available for all types of railway tractions in the near future.

I. Introduction

Railway is the one of the most popular and widely used ways for massive public transportation. The modern developing trends toward high speed, distributed propulsion by electrical multiple units (EMU) and increased passenger comfort require traction systems with higher efficiency, lower weight, and volume. One of the major obstructs is the conventional line frequency transformer (LFT). LFTs are bulky and heavy due to the nature of low operating frequency even with its efficiency being greatly compromised to increase the power density.