Patent ID: 8106621

Claim:
A control device comprising: a pulse width modulation (PWM) inverter unit that drives an induction motor; a slip calculator that calculates a first slip frequency of the induction motor; a current detector that detects motor current that passes through the induction motor; an adder that calculates a primary frequency by adding a speed command and a second slip frequency that are given; a command voltage generation unit that generates first command voltage from the primary frequency; a voltage error observer unit that estimates a command voltage error from the first command voltage and the motor current; a slip correction unit that calculates a slip correction amount from the command voltage error; an adder that calculates the second slip frequency by adding the first slip frequency and the slip correction amount; and a voltage error correction unit that corrects the first command voltage using the command voltage error and outputs second command voltage, wherein the PWM inverter unit applies the second command voltage to the induction motor.