Impedance-based Stability Analysis of Cascaded Dual-Active-Bridge Converters in Smart Transformer Microgrids

The recent advances in energy production and consumption have reshaped the electrical grid scenario. The trend is showing how power electronics converters are becoming increasingly important for the electrical energy transmission and distribution. In this framework, Smart Transformers (ST) can be adopted as interface between medium- and low-voltage grids, with the benefits of additional controllability and services. The dc-dc stage of ST provides the galvanic isolation and availability of DC links of MVDC and LVDC sides. This paper deals with the stability analysis of the cascaded connection case containing the dc-dc converter in ST and the one at the LVDC side, where the dual-active-bridge converters are selected as the dc-dc converters for investigation. The results of the impedance-based analysis show how the system stability can be challenged by the tuning of the voltage controllers.