A new SST topology comprising boost three-level AC/DC converters for applications in electric power distribution systems

Interest in integrating distributed generation into existing power distribution systems and achieving a more efficient, modern, reliable and versatile grid is leading to more research efforts on developing grid-interfaced converters such as the solid-state transformer. As current and voltage ratings of commercially available power semiconductor devices are normally below power ratings required in distribution systems (e.g., 13.8 kV), multiple modules must be connected in cascade configuration at the high-voltage side to reach higher voltage ratings as well as in parallel on the low-voltage side of to achieve high current levels. A new SST topology consisting of modular boost-based three-level AC-DC converters, high- or medium-frequency transformers with two secondary windings and four-leg ac-dc converters is presented in this paper. This topology when compared to similar approaches has fewer power conversion stages, lower voltage applied across the semiconductor devices on the high-voltage side (which reduces the number of modules), and lower current flowing through each device on the low-voltage side, leading to fewer parallel-connected devices. The feasibility of the proposed topology is experimentally validated on a 2 kW, 120 Vpk/ 10 Vdc scaled-down prototype.