Y10. Solid State Transformer


As a core center technology, the SST is the heart of the FREEDM System. It provides the control and physical interfaces that support three of the system’s major functions: plug-and-play, intelligent power management, and intelligent fault management. The overall research objective has always been to develop a reliable, efficient, cost-effective, compact device with bidirectional power flow operating between 7200 VAC and 400 VDC/240 VAC. Achieving these research objectives has required creativity and compromise.

The Principal Investigator for this project is Dr. Srdjan Lukic.


Previous generations of the SST design advanced understanding of the performance trade-offs but did not meet the overall objectives. Generations 1 and 2 suffered from reduced efficiency, reduced high-voltage capability and poor controllability. Generation 3 overcame some of these issues but required higher cost components and lacked certain functionality.

SST Generation 1


In year 10, researchers developed a new topology for Generation 4 that includes direct AC-AC conversion in parallel with an active filter. A modular approach allows the use of commercially available high-voltage power semiconductors embedded in custom packaging that provides robust short-circuit protection. Other advances include design of a high-voltage isolation transformer and a novel active harmonic filter with enhanced control bandwidth.