Power modules for electrified transport applications need to meet the requirement for ever higher power density while maintaining optimum reliability. For use in traction applications, SEMIKRON produces not only conventional IGBT diode and thyristor modules, but also integrated power modules (IPM) and power systems for these applications.

A particular challenge for main drives and auxiliary converters in electrified vehicles is the high rate of substantial fluctuations in voltage – e.g. resulting from over-voltages from short-term interruptions caused by disconnection of the pantograph.

Whereas, in mainline trains, drives and auxiliary power supply systems are usually connected to the overhead line via a medium-voltage transformer, the converters for trams, for example, operate directly on an overhead DC-line voltage of 600V to 1500V.

Main drive converter

The output range for central and separate wheel drives is between around 100 kW and 1 MW. Owing to the high input voltage range and the need to be able to feed back to the grid during braking operations, the converter has 4-quadrant topology. This means it comprises a single-phase IGBT line power converter – which can be operated as a step-up or step-down converter – the DC bus and a 3-phase output inverter for feeding one or more three-phase traction motors. The output voltage of the medium-voltage transformer, the DC link voltage and the supply voltage of the traction motors are used to determine whether the IGBT modules used have reverse blocking voltage of 1200 V, 1700 V or higher.

Main drive converters for trams or underground trains do not have a transformer. The line power converter is connected directly to the overhead line or conductor rail and, as a DC/DC converter (step-down converter), drops the input voltage to a regulated DC link voltage of, for example, 1100V for the use with 1700V IGBTs.

Block diagram of a converter for onboard mains systems in rail vehicles

Auxiliary converter

Auxiliary converters with outputs ranging between 10 kW and 250 kW are used to supply power to auxiliary units such as ventilation, air conditioning and lighting, as well as to the battery charger. These converters can be integrated into the main converter or be a self-contained unit.

The converter depicted above is connected via an input filter directly to the 750 V overhead line voltage, which is reduced by a step-down converter to a regulated input voltage for the converter. In contrast to the main drive converter, auxiliary converters need to be electrically isolated. In order to keep the necessary transformers as small and lightweight as possible, the DC voltage is transformed with inverters using the highest possible switching rates and then rectified again. Different DC voltage consumers can be supplied via the DC busbar. AC voltages with constant or variable frequency, for ventilation or air conditioning drives for example, are generated in inverters connected downstream.

SEMIKRON Products for rail vehicles