Design of Capacitors in SST

This paper deals with the design of all “power” capacitors in two variants of a solid-state transformer (SST) described in this work. SSTs are nowadays at the center of attention mainly due to reducing the size and weight of traction transformers in railway vehicles and in power transfer, where it should be part of an energy router that could replace the distributional transformer. In the case of three-stage SST, there are three types of capacitors: in submodules of a modular multilevel converter (MMC), in the MV-DC link, and on outputs of the galvanic insulation modules (DAB). In the case of two-stage SST, there are two types of capacitors: one type is in the DC link, and another type is on the outputs of the galvanic insulation modules, similarly as in the previous case. If we choose the same voltage levels for the DAB, we will get different numbers of DAB needed for the two variants of SSTs with different capacitors and medium frequency transformers (MF Tr).