Patent ID: 8080954

Claim:
An inverter apparatus wherein a plurality of element sets each comprising a pair of switching elements connected to each other in series are connected in parallel to each other relative to a DC power source to form an inverter circuit which converts a DC voltage of said DC power source into pseudo AC voltages with a plurality of pulse row-like phases and outputs said pseudo AC voltages, an output control circuit including a PWM generator capable of adjusting each phase of said pseudo AC voltages by pulse modulation is connected to said inverter circuit, and output voltages from said inverter circuit are applied to a power supplied load, characterized in that an average voltage of respective phases of said output voltages applied to said power supplied load is detected as a virtual neutral voltage corresponding to a neutral voltage of said power supplied load by detecting a voltage at a common node where respective phases of a voltage detecting circuit provided between said inverter circuit and said power supplied load are connected, and by feeding back said detected virtual neutral voltage for controlling an output duty of each phase by said PWM generator, said output voltage of each phase from said inverter circuit is controlled so as to become a target output voltage, wherein a high voltage value of said virtual neutral voltage is detected during a period of time when voltage values of respective phases of said output voltages from said inverter circuit are all high, and said output duty of each phase is variably controlled by calculation based on the following equation: output duty =target output voltage/high voltage value of detected virtual neutral voltage, in which a state of said high voltage value of said output voltage means a state in which said pulse row-like pseudo AC voltage indicates a maximum voltage value.