Research on High-Performance Power Electronic Traction Transformers for the Novel Medium Voltage DC Railway Electrification System

This thesis is the product of a European Union project in collaboration with Shift2Rail and University of Birmingham (UoB), called Flexible MVDC-ERS. The PhD student from Technical University of Cluj-Napoca has been working on a major part of the 41 months project, related to the power electronic traction transformer (PETT) of the proposed novel medium voltage direct current (MVDC) smart railway electrification line.
The objectives of the thesis (and the project) were to research and develop modern PETTs suitable for a new railway electrification system. In order to demonstrate the concept of the proposed rail network, detailed literature reviews, full-scale simulation models and experimental prototypes were developed for both the substation and the traction system by UoB and TUCN. This thesis successfully achieved the research objectives and the concept validation.

Thesis originality and personal contributions

The personal contributions brought by this work are:

1. Detailed literature research and comparative analysis of railway electrification systems, power electronic traction transformers and wide-band-gap semiconductors.
2. Definition of suitable topological families for DC power electronic traction transformers in the application of a novel medium voltage DC railway electrification smart network.
3. Proposal and analysis of two converter topologies for the modular traction system, including their controllers.
4. Mathematical modeling of the two topologies, including their control loop design.
5. Comparative analysis of three different snubber circuits for high-voltage spikes reduction. The study includes their mathematical model and design procedure as well.
6. Introduction of a regenerative active clamping snubber with a novel control mechanism, including its detailed mathematical model and design procedure.
7. Development of automated design sheets in Mathcad for both converter topologies.
8. Automated design sheet in Mathcad for the PI and PID controllers of the converter modules, using the frequency domain methods.
9. The full-scale simulation model of the DC power electronic traction transformer system and its simple control. The system was implemented in Matlab/Simulink with both converter topologies proposed and designed previously.
10. Implementing and testing experimentally the converter modules. The validation process was made through comparison of experimental results with simulation results, which were also compared with the values obtained in the Mathcad design sheet, using the mathematical model of the converters. Finally, the two topologies were compared.

PhD THESIS – ABSTRACT: Click here