Comparative Evaluation of Three-Phase-Unfolder-Based MVAC-LVDC Solid-State Transformers

Abstract:
Solid-state transformers (SSTs) for MVac-LVdc conversion, e.g., in future high-power EV charging stations, should feature low conversion losses and low complexity. Therefore, topologies based on a three-phase unfolder, i.e., a six-pulse rectifier, which thus eliminate PFC rectifier input stages and instead rely on modular dc-dc isolation stages for sinusoidal input current shaping, are of high interest. This paper discusses state-of-the-art and new topologies in this category, explains the operating principles of the systems, and, finally, provides a comparative evaluation of the SST topologies concerning realization effort, component stresses, and general complexity.