Single-Stage MVAC-LVDC SST with Reduced Current Stress and Switch Count

Conventional high-power DC applications requiring medium voltage (MV) grid integration such as renewable, electric vehicle fast-charging use Line Frequency Transformers (LFT) to step down MV to low voltage (LV) before connecting to a AC-DC converter. LFTs are quite heavy and bulky which reduces the overall power density and therefore solid state transformers have the potential to replace them in such applications. Cascaded multi level configuration with input series output parallel combination per phase has emerged as a promising solution among different MVAC to LVDC solutions. The power density and reliability can be further improved by having single stage solution by eliminating the requirement of large DC link capacitors required per phase. However, large device count and high-frequency current stress is still a challenge in these solutions which needs to be solved. This paper introduces a novel single-stage dual-active-bridge-derived solid-state transformer designed to minimize device count, current stress, switching losses, and enhance improve overall efficiency and power density. Validation using simulation software and experimental verification is presented with a scaled down laboratory-scale prototype.