Current source inverter based cascaded solid state transformer for AC to DC power conversion

There are applications like railway traction system where power converters for HVAC to MVDC or MDAC to LVDC are required with a high power/weight ratio. The conventional way is to use heavy line frequency or medium frequency transformers followed by a controlled rectifier. The availability of high voltage SiC devices has made it possible to raise the switching frequency to higher value and hence the size and weight of the transformer can be reduced. This paper proposes a cascaded current source converter based topology with high frequency isolation as a replacement of the huge line frequency transformer. The paper also presents experimental results as a validation of the functionality of the converter.