FUNDRES (FUture UNified DC Railway Electrification System) is a €0.75 million project led by LAPLACE (Laboratory on Plasma and Conversion of Energy, University of Toulouse, France) in collaboration with three other European partners from Italy, Switzerland and France, namely: the Polytechnic University of Milan (Politecnico di Milano – POLIMI), the Swiss Federal Institute of Technology in Lausanne (École Polytechnique Fédérale de Lausanne – EPFL) and the International Union of Railways (UIC). The two-year project ended in November 2021.
The webinar was attended by 40 participants representing infrastructure managers, railway undertakings, industry and academia.
All of the presentations delivered during the webinar can be downloaded here.
Project achievements
The project examined the interface between the future 9 kV DC power system and the public grid. This work was carried out on a research platform dedicated to the modular multilevel converter (MMC). A real-time Hardware in the Loop (RT-HIL) system was developed for both the MMC and the railway system so that several different scenarios could be studied. The RT-HIL system was implemented on real-time simulation equipment (RT-Box) designed by PLEXIM for power electronics applications. Relevant electrical waveforms were recorded in real time, taking into account the movement of the train. In particular, the study demonstrated the possibility of restoring braking energy to the public grid. In parallel with this work, two MMC prototypes (5 kV/250 kVA - 48 cells) were built, with one expected to be finished in January 2022. Due to the global semi-conductor shortage, this outstanding test platform will be used to set up an experimental demonstration at the future DC railway electrification system’s actual voltage level in January 2022, when both MMCs will be complete.
A digital twin (DT) for the future 9 kV DC power system was proposed as part of the project. The DT was implemented in MATLAB/Simulink software. It includes the traction substations, the railway traction circuit (contact line and locomotives), renewable energy sources (wind farms and solar plants), the energy storage system and the electrical vehicle charging infrastructure. An energy management system considering various scenarios was also proposed. The DT made it possible to demonstrate that renewable sources can feasibly be integrated into a railway traction system, taking into account various power flows due to rail traffic and the natural variability of renewable energy sources.
Experimental tests on one elementary module of a solid state transformer (SST) were carried out, achieving outstanding results in terms of energy efficiency. An electrical model of a three-wire DC power supply, including SSTs, was proposed to prepare for a transition between 1.5 kV and 9 kV electrification systems. A full 3D design of a 9 kV/1.5 kV SST in a container configuration was completed. The integration of the SST into a 1.5 kV electrification system was studied using a model implemented in PLECS simulation software, with the simulation results demonstrating full compatibility.
Despite its short duration and thanks to the academic work carried out, FUNDRES has demonstrated the relevance of developing a new DC railway electrification system. In the long term, it will pave the way toward a new European standard for DC voltage levels, which in turn will improve rolling stock interoperability.
Outlook
Although electric power suppliers are increasingly considering the prospect of developing DC networks, introducing a new MVDC electrification system in the railway domain will not be easy. It will take time and must be considered over a period of several decades.
Several obstacles remain to be overcome, such as:
- development of traction chains capable of operating under 9 kV DC,
- development of circuit breakers for interrupting short-circuit currents under 9 kV DC,
- drafting of standards to define the characteristics of this new system and management rules for energy flows.
The work carried out at laboratory scale in the context of the FUNDRES project has demonstrated feasibility; experiments on pilot sites must now be considered. Proof of concept is essential for rail operators. Beyond the desire to innovate, this requires access to the appropriate financial means.
For more information, please visit the FUNDRES website
