Patent ID: 8076896

Claim:
An inverter controller comprising: an AC motor as a load, a rectifying circuit for converting AC power from an AC power source into DC power, a smoothing capacitor for smoothing a DC voltage from the rectifying circuit, an inverter circuit for converting DC power supplied via the smoothing capacitor into a desired frequency, a current detection circuit for detecting an output current of the inverter circuit, a voltage detection circuit for detecting a terminal voltage (Vpn) of the smoothing capacitor, a voltage command calculation circuit for calculating a voltage command to the AC motor, a speed command calculation circuit for calculating a speed command to be used when it is determined that the AC power source is in a power failure state or when the terminal voltage (Vpn) reaches a certain value, wherein the speed command calculation circuit includes: a power calculation circuit for calculating a power output value (P) based on the output current and the voltage command, and a power target calculation circuit for calculating a power output target value (Pref) based on the terminal voltage (Vpn), a previously-set target voltage (Vpnc) of the terminal voltage (Vpn) for the power failure state, and a capacity (C) of the smoothing capacitor, and wherein the speed command calculation circuit calculates the speed command based on the power output target value (Pref) and the power output value (P).