I. Introduction
During the last decades, factors such as changes in the power grid structure, the increase of penetration levels of renewables, the implementation of dc grids, and the need to offer premium power quality to customers have motivated utilities to implement new power electronic interfaces (PEIs) to modernize the conventional power distribution system. One of the most helpful and promising PEI in the future power grids is the so-called solid-state transformer (SST), which has been proposed to replace the bulky fundamental-frequency transformers for several applications [1]–[7]. In addition to the functionalities of conventional transformers (e.g., galvanic isolation between networks and voltage matching between two voltage levels), the SST is capable of controlling the power flow between networks, limiting fault currents, integrating energy storage units, compensating for reactive power, improving power quality, and many others. These assets make the SST a promising technology in future smart grids at any voltage and power level [3]–[5].