In AC electric trains, power electronic traction transformers (PETT) are multilevel single phase AC/DC converters connected to the AC medium voltage overhead line. For indirect topologies, DC/DC isolated converters are key elements of PETTs. This paper shows a method to design such DC/DC converters, and several variants are considered. Finally, the comparison results, in the case of a 25 kV / 50 Hz power supply and 3.3 kV SiC MOSFETs, show that the variant with a resonant AC link, with only one controlled bridge and a switching frequency lower than the resonant frequency, offers the best efficiency at rated power for a given volume.

Fail-to-short packages, which can still carry current after the failure of their semiconductor devices, are required for HVDC applications. However, all existing solutions are dedicated to silicon components. Here, a fail-to-short package is proposed for SiC devices. Its manufacturing process is described. 4 modules are built and submitted to intense short circuit currents (up to 2000 A). It is found that they offer a stable short-circuit failure mode, providing that the modules are mechanically clamped to prevent separation during the surge current test.

This paper studies the role of DC-DC converters in the protection of HVDC grids acting as firewalls to stop the propagation of faults. The effects of blocking the converter or actively controlling its operation during faults are presented.The results demonstrate the capabilities of DC-DC converters beyond DC voltage transformation.

Why are ceramic materials (when compared to organic materials) necessary for the purpose of electric isolation in power modules, especially for medium voltage applications...

This paper presents a methodology for the modelling of a 25 kV-50 Hz railway infrastructure, for frequencies from 0 to 5 kHz. It aims to quantify the amplifications of current and voltage harmonics generated by on-board converters into the infrastructure. A circuit is developed to model the skin effect in the overhead line for time-domain simulations. A new approach, based on state space representation and transfer functions, is also proposed to analyse the interactions between trains.