Voltage Adjustable Capacitor Isolated Solid State Transformer

This article proposes a voltage-adjustable capacitor isolated solid-state transformer (ACISST) to link the medium-voltage direct current distribution and low-voltage direct current distribution. Compared with traditional isolated bidirectional dc–dc converter, the proposed ACISST does not contain high-frequency transformer in base modules (BMs). The galvanic isolation between the primary side and the secondary side of the ACISST is realized by the isolation capacitor as quasi-isolation. The elimination of the high-frequency transformer eliminates the core losses of magnetic elements, improves the conversion efficiency to a certain extent, and reduces the weight of the ACISST. The voltage-adjustable unit realizes the secondary voltage regulation of stable control when the primary-side voltage fluctuates in an acceptable range or load power varies. Bidirectional power flowing is one of the features of ACISST, which is based on the bidirectional power flowing characteristic of BM and simplified dual active bridge. Simulation and experimental results are presented to validate the theoretical analysis.