Control strategy for dual active bridge based DC solid state transformer

Dual active bridge (DAB) with input-series output-parallel (ISOP) structure is capable to interconnect low voltage DC micro grid with medium/high voltage DC distribution grid, named as DC solid state transformer (DCSST). This paper presents a combined decoupling control strategy for the DCSST, which aims to achieve input voltage sharing among sub-modules and enhance voltage control of the parallel output. By deriving small signal model and transfer function of DCSST, the decoupling conditions between the output voltage control and the input voltage sharing are identified, and the loop gains are well-tuned as well. Simulation and experimental results are provided for verification of the controller design.