A solid state transformer uses power electronics instead of a line-frequency copper/iron core to convert medium-voltage AC toward a DC bus. Design goals include bidirectional flow and grid-interface control.
In the Joule Junction platform, SST is a DC BUS component: MV AC in, 800V DC out, with PCS handling bidirectional AC↔DC duties at the edge. Maturity is design-target.
Specify SST when the project story needs MV interface density and DC distribution; conventional transformers remain valid where AC distribution is the architecture choice.