The power electronic traction transformer (PETT) topology is composed of n cells connected in input in series and in output in parallel. The input is supplied by an AC catenary and the output supplies a traction inverter. Each cell consists in :
- An AC-DC converter (H-bridge). The n front end converters are called AFEC (Active Front End Converter) ;
- An intermediate DC bus ;
- An isolated DC-DC converter with a medium frequency transformer.
This PETT topology can be used with a MVDC catenary, configuring the AFEC switches in the right state. However, this may result in rather high losses. The idea proposed here consists in adding some switchgear on the intermediate buses to supply it with a MVDC catenary, reducing the losses.
In the improved PETT topology, the switchgear is added between the intermediate DC buses, between the pantograph and the intermediate
bus of the first cell and between the earth and the intermediate bus of the last cell. To connect PETT to a MVDC catenary, the switches are configured after having turned off the power. Thus, the intermediate buses are connected in series/parallel and the pantograph supplies directly the intermediate buses.