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.