Solid-State Transformers: A Review—Part II: Modularity and Applications

The Solid-State Transformer (SST) is a complex conversion device that intends to replace the Low-Frequency Transformers (LFTs) used in various power applications with Medium- or High-Frequency Transformers (MFTs/HFTs) that integrate modular converter structures as their input and output stages. The purpose is to obtain additional capabilities, such as power factor correction, voltage control, and interconnection of distributed supplies, among others, while reducing the overall volume. Given the expansive research conducted in this area in the past years, the volume of information available is large, so the main contribution of this paper is a new method of classification based on the modular construction of the SST derived from its applications and available constructive degrees of freedom. This paper can be considered the second part of a broader review in which the first part presented the fundamental converter roles and topologies. As a continuation, this paper aims to expand the definition of modularity to the entire SST structure and analyze how the converters can be combined in order to achieve the desired SST functionality. Three areas of interest are chosen: partitioning of power, phase modularity, and port configuration. The partitioning of power analyzes the fundamental switching cells and the arrangement of the converters across stages. Phase modularity details the construction of multiphase-system SSTs. Finally, the types of input/output ports, their placements, and roles are discussed. These characteristics are presented together with the applications in which they were suggested to give a broader context.