Voltage and current balance control for the ISOP converter-based power electronic transformer

The power electronic transformer (PET) is a key interface for both ac and dc systems in future smart grid. As a topology suitable for high power applications, the input-series output-paralleled (ISOP) converter-based PET normally consists of three-stage, the input cascaded ac/dc input stage, the high-frequency transformer dc/dc isolated stage, and the optional dc/ac output stage. For the ISOP topology, the difference of sub-module parameters may cause the unbalanced voltage and current issues. This paper firstly investigates Impact of the different module parameters on the input dc voltage and output dc current. To resolve the unbalanced voltage, a method based on single-phase dq decoupled control is proposed. In addition, a new control strategy is introduced in dual active bridge (DAB) parallel modules to realize the power balance. Finally, the proposed voltage and current control methods are verified by the simulation studies using MATLAB/Simulink.