Patent ID: 7499291

Claim:
A converter system comprising: an IGBT converter for converting an AC power to a DC power or the DC power to the AC power; an open Y-Y transformer and a Y-Δ transformer for stepping up or stepping down the AC power having a predetermined magnitude; a capacitor for dividing a DC voltage; and a DC auxiliary circuit comprising a normal transformer and a half-bridge for overlapping a pulse type input voltage to increase the number of pulses of an output waveform, wherein the IGBT converter comprises a first converter connected to the Y-Y transformer and a second converter connected to the Y-Δ transformer, the capacitor comprises a first DC capacitor connected between a primary side terminal of the transformer of the DC auxiliary circuit and a positive terminal of the first converter, and a second DC capacitor connected between the primary side terminal of the transformer of the DC auxiliary circuit and a negative terminal of the second converter, and the half-bridge of the DC auxiliary circuit comprises a 3-level half-bridge consisting of first through fourth switching elements connected to the first DC capacitor and the second DC capacitor in parallel and connected to secondary side terminals of the transformer.