A Simple Control Method without Voltage Balance Algorithm for Modular Solid-State Transformer

In this paper, a new control method for the modular solid-state transformer (SST) is proposed. The modular structure of SST to be studied in the paper is a three-stage configuration consisting of the cascaded H-Bridge (CHB) converter, dual active bridge (DAB) converter, and inverter. In the proposed method, the CHB converter controls the grid side input current and the secondary DC-link voltage, while the DAB modules control each primary floating DC-link voltage. The proposed method does not need an additional balance control algorithm for primary DC-link voltages and reduces the complex communication requirements, so it can significantly simplify the system structure and operation. Consequently, it is advantageous to increase the number of SST modules or extend it to three-phase systems. The experimental results in a 5-kW SST prototype are provided to verify the validity of the proposed control method.