Operation of a three phase solid state-Transformer under unbalanced load conditions

Solid state transformers (SSTs) have found widespread power applications in traction locomotives, distribution systems, smart grids, etc., where they are going to replace conventional transformers and associated power enhancement equipments to provide better power quality features and functionalities. An eminent structure of SST comprises of three power conversion stages: input (AC-DC), isolation (DC-DC), and output (DC-AC). Multilevel converters are incorporated in several SSTs for operating at high voltage levels. This paper presents a three phase multilevel converter based SST (MCSST) which contains Cascaded H Bridge (CHB) multilevel converters in its input stage. Most of the reported topologies of MCSST have a common low voltage DC (LVDC) bus and a common control block for the entire SST structure. The presented MCSST consists of three independent phase modules and each phase module is controlled separately. Therefore, the outputs of these modules can be applied to both three phase loads as well as three independent single phase loads. Such a configuration can also be used to operate effectively under unbalanced load conditions. The discussed analysis of the reported work is verified using PSCAD/EMTDC simulation results.