Patent ID: 7612518

Claim:
An inverter apparatus comprising: a converter portion for converting an alternating current voltage into a direct current voltage, a capacitor for smoothing the direct current voltage, an inverter portion for driving an alternating current motor by converting the direct current voltage into an alternating current, a current converting portion for generating a detecting value of a current flowing in the motor, and a PWM calculating portion for generating a signal for driving a gate of a power element, a direct current voltage detecting portion for detecting the direct current voltage; a first filter portion and a second filter portion constituting two low pass filters for filtering an output of the direct current voltage detecting portion; a speed reducing rate setting portion for setting a speed reducing time period of the motor; a speed reducing rate calculating portion for calculating a frequency of driving the motor from an output of the first filter portion and an output of the speed reducing rate setting portion; and a voltage command correcting portion for correcting a voltage command from an output of the second filter portion and a given voltage command, wherein in speed reducing, a time constant of the second filter portion is constituted by 10 through 10000 times as much as a time constant of the first filter portion.