A solid-state transformer (SST), power electronic transformer (PET), or electronic power transformer is actually an AC-to-AC converter, a type of

electric power converter In all fields of electrical engineering, power conversion is the process of converting electric energy from one form to another. A power converter is an electrical or electro-mechanical device for converting electrical energy. A power converter c ...

that replaces a conventional

transformer A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...

used in AC

electric power distribution Electric power distribution is the final stage in the delivery of electric power; it carries electricity from the transmission system to individual consumers. Distribution substations connect to the transmission system and lower the transmissi ...

. It is more complex than a conventional transformer operating at

utility frequency The utility frequency, (power) line frequency (American English) or mains frequency (British English) is the nominal frequency of the oscillations of alternating current (AC) in a wide area synchronous grid transmitted from a power station to th ...

, but it can be smaller and more efficient than a conventional transformer because it operates at high frequency. The main types are "true" AC-to-AC converter (with no DC stages) and AC-to-DC-to-DC-to-AC converter (in which an active

rectifier A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The reverse operation (converting DC to AC) is performed by an Power ...

supplies power to a

DC-to-DC converter A DC-to-DC converter is an electronic circuit or electromechanical device that converts a source of direct current (DC) from one voltage level to another. It is a type of electric power converter. Power levels range from very low (small batteries) ...

, which supplies power to a

power inverter A power inverter, inverter or invertor is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC). The resulting AC frequency obtained depends on the particular device employed. Inverters do the opp ...

). A solid-state transformer usually contains a transformer, inside the AC-to-AC converter or DC-to-DC converter, which provides electrical isolation and carries the full power. This transformer is smaller due to smaller DC-DC inverting stages between transformer coils, which consequently mean smaller transformer coils required to step up or step down voltages. A solid-state transformer can actively regulate voltage and current. Some can convert single-phase power to three-phase power and vice versa. Variations can input or output DC power to reduce the number of conversions, for greater end-to-end efficiency. A Modular Solid-state transformer consists of several high-frequency transformers and is similar to a

Multi-level converter A multi-level converter (MLC) is a method of generating high-voltage wave-forms from lower-voltage components. MLC origins go back over a hundred years, when in the 1880s, the advantages of DC long-distance transmission became evident. Modular mul ...

. As a complex electronic circuit, it must be designed to withstand lightning and other surges. Solid-state transformer is an emerging technology.

References

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