Patent ID: 8327670

Claim:
A motor controller, comprising: a vector controller that controls a permanent magnet motor including a rotor being provided with a permanent magnet having a coercivity low enough to allow modification in amount of magnetization and that executes a vector control by detecting current flowing at the permanent magnet motor; a speed/position detector that detects a rotational speed and a rotational position of the permanent magnet motor; a magnetization controller that increases or decreases the magnetization of the permanent magnet depending on the rotational position of the permanent magnet motor through adjustment in status of the magnetization of the permanent magnet by way of armature counteraction; a demagnetization detector that detects a decrease in the magnetization of the permanent magnet magnetized by the magnetization controller during operation of the permanent magnet motor; an induced voltage command determiner that determines an induced voltage command that is optimal for operational status of the permanent magnet motor; and an induced voltage detector that detects an induced voltage occurring at the permanent magnet motor by calculation; wherein the demagnetization detector detects the decrease in the magnetization of the permanent magnet by comparing the induced voltage command and the detected induced voltage and judging that the detected induced voltage is reduced by a predetermined percentage or predetermined value relative to the induced voltage command.