PURPOSE: To convert three-phase AC into single-phase AC simply and easily by synthesizing a secondary-side output from a three-phase connection using three single-phase transformers in succession through the single-phase transformers.

CONSTITUTION: The primary sides of three single-phase transformers are star- connected or delta-connected, and other two are wound counterclockwise (clockwise winding) when one winding among three secondary connections is wound clockwise (counterclockwise winding) on the secondary sides. Reverse currents on the primary sides of outputs from the secondary sides are prevented by a semiconductor element inserted on the secondary sides. The AC of outputs on two secondary sides are synthesized by No.1 transformer (d), and reverse currents are prevented by the semiconductor element inserted on the secondary side of No.1 transformer (d). AC synthesized by No.1 transformer (d) and AC not synthesized are synthesized by No.2 transformer (e), and converted into singl-phase AC.