Solid-State Transformers in Modern Distribution Grids: A Comprehensive Review of Principles, Topologies, Key Technologies, Applications, and Challenges

With the increasing complexity of distribution networks, higher demands have been placed on systems for efficient power conversion. The solid-state transformer (SST), which integrates power electronic converters with a high-frequency transformer (HFT), has become a major research focus in end-user power supply applications. This paper first compares the technical advantages of SSTs over conventional transformers and systematically explains their operating principles. It then reviews the development trajectory of SSTs in terms of topological evolution, prototype-based engineering validation, and the application of emerging materials. Next, it classifies and summarizes the current mainstream topologies and identifies core devices and key control technologies, including SiC devices and advanced soft magnetic materials. Finally, it introduces representative SST applications in data centers, smart grids, and charging stations and summarizes and discusses future research directions and challenges. This paper clarifies the technological evolution and existing bottlenecks of SSTs, provides a useful reference for the high-quality and highly flexible operation of distribution networks, and offers clear guidance and directions for the subsequent engineering deployment of SSTs.