Direct AC–AC Solid-State Transformer Based on Hybrid DAB

This article presents a direct ac–ac solid-state transformer (SST) based on hybrid dual active bridge (DAB) converter with reduced switches. The presented SST consists of a full-bridge rectifier on the grid side and a half-bridge inverter on the load side with line-frequency, and a hybrid DAB converter with high frequency. Among them, the hybrid DAB consists of a half-bridge on the primary side and a full-bridge on the secondary side. By sharing a bridge arm between the DAB and the inverter, reduced switches and improved power density are achieved. Besides, there is no power pulsation problem with double line-frequency, and thus electrolytic capacitorless structure is adopted in the developed topology. In terms of control, the DAB adopts single-phase shift control to realize output voltage regulation. Moreover, this article analyzes the steady-state operation and the zero-voltage switching (ZVS) characteristics. As a result, the presented SST has the advantages of low components, high power density, and no double line-frequency power pulsation. Finally, experimental results from a 2 kW prototype are provided to verify the feasibility and correctness of the presented methods.