Several companies are working on technologies that could replace large traditional power transformers with power semiconductors and smaller transformers mounted on circuit boards. Although they are called solid-state transformers, they are really power converters.
The figure below is a conceptual circuit for a “solid-state transformer” that accepts a three-phase 60 Hz high-voltage input and provides a 60 Hz lower-voltage output. The transistors could be SiC or GaN types with the appropriate specifications. The input circuit converts 60 Hz high voltage ac input to a dc voltage. Then, the dc produces an ac voltage of 10 to 20 kHz that is applied to a step-down transformer. The transformer output is converted to dc and applied to an inverter to produce a lower voltage 60 Hz ac output. The transformer is necessary to provide isolation between the input and output. An advantage of this approach is reduction in size and weight of the transformer because it can operate at a much higher frequency than a 60Hz power transformer.
There may be more to this than meets the eye. Michael Kanellos in his March 2011 article Next for the Grid: Solid State Transformer, published by Greentech Media, wrote, “This process could begin to pave the way for a number of improvements in the way that power gets delivered. Integrating and managing renewable power and electrical storage could become easier. Microgrids could be deployed much more rapidly. Grid efficiency could conceivably be increased by up to 8% to 10% because of lower conversion and transmission losses.”
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