PURPOSE: To reduce the rated capacity of inverter remarkably without increasing the total number of electrolytic capacitors so much by connecting a second DC capacitor, when DC input voltage to the inverter drops below a predetermined level due to instantaneous voltage drop compensation, thereby adding voltages from first and second DC capacitors in series and applying thus added voltage on the inverter.
CONSTITUTION: A DC filter capacitor 3 is charged with DC rated input voltage VDC1 of an inverter 4 and a DC filter capacitor 13 is charged with a voltage VDC2 lower than VDC1. The DC filter capacitor 13 is normally isolated from the inverter 4 and when the DC input voltage VDC of the inverter 4 drops below a predetermined level due to discharge of the DC filter capacitor 3 for the purpose of instantaneous voltage drop compensation, the DC filter capacitor 13 is connected and the voltages of the DC filter capacitors 3, 13 are added in series then applied on the inverter 4.
MIZUKI KATSUFUSA
KURIO NOBUHIRO
