An Optimized Start-up Method for Modular Cascaded AC/DC Power Electronic Transformer with Minimized Input-Inrush Current in Dual Active Bridge

The modular cascaded power electronic transformers (PETs) designed for interfacing AC and DC grids are mostly composed of active front end (AFE) and dual active bridges (DABs). Due to the remarkable difference between primary side and secondary side capacitor voltages of DAB at start-up, high input-inrush current will occur if the phase-shift-control (PSC) of DAB is directly employed, which can pose damage to power devices. This paper proposes a novel soft start-up method for DABs in PET with fast pre-charge process. The duty cycle of primary bridge is dynamically adjusted to precisely limit the peak of input-inrush current, and the regulating range is also enlarged.