A Study on the Evolution of Solid State Transformer Technologies and Applications

The advancements in power electronics have enabled the building of solid-state transformers (SSTs) to meet the demands of smart grids. An SST is an AC/AC solid-state power conversion system. Typically these SSTs can be classified based on various parameters like series/parallel interconnection, number of power conversion stages, degree of phase modularity, etc. This paper presents a survey of the work carried out to date on SSTs with multi-stage power conversion. Furthermore, the paper highlights the SSTs that enable medium voltage grid interconnection, which is enabled by high voltage (HV) SiC power devices. The design, control, development, and testing of SST with HV SiC 10 kV MOSFETs and 15 kV SiC IGBTs are presented, and a pilot demonstration for the Navy of a medium voltage (MV) 4160 V, 100 kVA SST for “Mobile Utility Support Equipment (MUSE)” based applications enabled by SiC 10 kV MOSFETs will be discussed. A Medium-Voltage Asynchronous Microgrid Power Conditioning System (Microgrid PCS), or MV-MV SST, enabled by HV SiC series-connected power devices to connect, disconnect, and enable power flow between asynchronously connected microgrids and grids is presented. The paper addresses the developed SST prototypes and provides analysis based on the related applications. The analysis also discusses the challenges and future trends regarding the implementation of SST.