Control device for alternating current motor

A control device for alternating current motors configured to perform a power supply control of an alternating current motor comprising permanent magnets, the control device comprising a computer system including a central processing unit, the computer system being configured to provide:

• a voltage instruction calculation part calculating voltage instruction values on the basis of an output torque instruction to be supplied to the alternating current motor;
• an electric power conversion unit converting a direct current power to an alternating current power on the basis of the voltage instruction values, and supplying the alternating current power to the alternating current motor;
• a magnetic flux change amount estimation part calculating a magnetic flux change amount estimation value which is a deviation of a real magnetic flux amount of the permanent magnets of the alternating current motor from a standard magnetic flux amount, where the standard magnetic flux amount of the permanent magnets is an amount when no demagnetization has occurred in the permanent magnets;
• and
• a demagnetization detection part detecting occurrence of demagnetization of the permanent magnets when the magnetic flux change amount estimation value calculated by the magnetic flux change amount estimation part is lower than a detection threshold value, wherein
• the magnetic flux change amount estimation part comprises:
• a real voltage estimation part estimating a d axis real voltage and a q axis real voltage to be supplied to the alternating current motor, or obtaining voltage detection values as the d axis real voltage and the q axis real voltage, correlated with the voltage instruction values;
• a standard voltage calculation part calculating a d axis standard voltage and a q axis standard voltage to be supplied to the alternating current motor in a standard state of the alternating current motor on the basis of an electrical angular speed and a current of the alternating current motor;
• a magnetic flux change amount estimation value calculation part calculating a basic magnetic flux change amount estimation value on the basis of a deviation of a specific value from the q axis standard voltage, where the specific value is obtained by multiplying a q axis real voltage with a ratio of the d axis standard voltage and the d axis real voltage;
• and
• a magnetic flux change amount estimation value correction part calculating the magnetic flux change amount estimation value by correcting the basic magnetic flux change amount estimation value relatively to the detection threshold value on the basis of characteristic change of the alternating current motor in a demagnetization state of the permanent magnets of the alternating current motor.