Motor controller and drum washing machine

1. 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.

2. The motor controller according to claim 1 , wherein the magnetization controller, when the decrease in the magnetization of the permanent magnet is detected by the demagnetization detector, increases the magnetization of the permanent magnet when a q-axis current of the permanent magnet motor is reduced below a predetermined value after having exceeded the predetermined value.

3. The motor controller according to claim 1 , wherein the magnetization controller, when the decrease in the magnetization of the permanent magnet is detected by the demagnetization detector, increases the magnetization of the permanent magnet when a variation percentage or a variation range of a q-axis current amplitude of the permanent magnet motor is equal to or less than a predetermined value.

4. The motor controller according to claim 1 , wherein the magnetization controller, when the decrease in the magnetization of the permanent magnet is detected by the demagnetization detector, increases the magnetization of the permanent magnet when an average of a q-axis current amplitude within a predetermined time period is equal to or less than a predetermined value.

5. A drum washing machine, comprising:

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

a motor controller including:

a vector controller that controls the permanent magnet motor 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; and

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;

wherein a washing operation is executed by rotating a drum containing laundry by a rotational drive force generated by the permanent magnet motor, and

wherein the demagnetization detector detects the decrease in the magnetization of the permanent magnet when a maximum value of a q-axis current at activation of the permanent magnet motor for starting a wash or a rinse step exceeds a predetermined value.

6. The drum washing machine according to claim 5 , wherein the magnetization controller, when the decrease in the magnetization of the permanent magnet is detected by the demagnetization detector, increases the magnetization of the permanent magnet when the rotational speed of the permanent magnet motor is constant during a wash or a rinse step.

7. The drum washing machine according to claim 5 , wherein the magnetization controller, when the decrease in the magnetization of the permanent magnet is detected by the demagnetization detector, increases the magnetization of the permanent magnet when the permanent magnet motor is rotated in one direction for a predetermined time period or more during a wash or a rinse step.

8. The drum washing machine according to claim 5 , wherein the magnetization controller, when the decrease in the magnetization of the permanent magnet is detected by the demagnetization detector, increases the magnetization of the permanent magnet when a q-axis current of the permanent magnet is reduced below a predetermined value after having exceeded the predetermined value.

9. The drum washing machine according to claim 8 , wherein the magnetization controller, when the decrease in the magnetization of the permanent magnet is detected by the demagnetization detector, increases the magnetization of the permanent magnet when the rotational speed of the permanent magnet motor is constant during a wash or a rinse step.

10. The drum washing machine according to claim 8 , wherein the magnetization controller, when the decrease in the magnetization of the permanent magnet is detected by the demagnetization detector, increases the magnetization of the permanent magnet when the permanent magnet motor is rotated in one direction for a predetermined time period or more during a wash or a rinse step.

11. The drum washing machine according to claim 5 , wherein the magnetization controller, when the decrease in the magnetization of the permanent magnet is detected by the demagnetization detector, increases the magnetization of the permanent magnet when a variation percentage or a variation range of a q-axis current amplitude of the permanent magnet motor is equal to or less than a predetermined value.

12. The drum washing machine according to claim 11 , wherein the magnetization controller, when the decrease in the magnetization of the permanent magnet is detected by the demagnetization detector, increases the magnetization of the permanent magnet when the rotational speed of the permanent magnet motor is constant during a wash or a rinse step.

13. The drum washing machine according to claim 11 , wherein the magnetization controller, when the decrease in the magnetization of the permanent magnet is detected by the demagnetization detector, increases the magnetization of the permanent magnet when the permanent magnet motor is rotated in one direction for a predetermined time period or more during a wash or a rinse step.

14. The drum washing machine according to claim 5 , wherein the magnetization controller, when the decrease in the magnetization of the permanent magnet is detected by the demagnetization detector, increases the magnetization of the permanent magnet when an average of a q-axis current amplitude within a predetermined time period is equal to or less than a predetermined value.

15. The drum washing machine according to claim 14 , wherein the magnetization controller, when the decrease in the magnetization of the permanent magnet is detected by the demagnetization detector, increases the magnetization of the permanent magnet when the rotational speed of the permanent magnet motor is constant during a wash or a rinse step.

16. The drum washing machine according to claim 14 , wherein the magnetization controller, when the decrease in the magnetization of the permanent magnet is detected by the demagnetization detector, increases the magnetization of the permanent magnet when the permanent magnet motor is rotated in one direction for a predetermined time period or more during a wash or a rinse step.

17. A motor controller, comprising:

a vector controller that controls a permanent magnet motor 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; and

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;

wherein the demagnetization detector detects the decrease in the magnetization of the permanent magnet when a maximum value of a q-axis current at activation of the permanent magnet motor exceeds a predetermined value.

18. The motor controller according to claim 17 , wherein the magnetization controller, when the decrease in the magnetization of the permanent magnet is detected by the demagnetization detector, increases the magnetization of the permanent magnet when a q-axis current of the permanent magnet motor is reduced below a predetermined value after having exceeded the predetermined value.

19. The motor controller according to claim 17 , wherein the magnetization controller, when the decrease in the magnetization of the permanent magnet is detected by the demagnetization detector, increases the magnetization of the permanent magnet when a variation percentage or a variation range of a q-axis current amplitude of the permanent magnet motor is equal to or less than a predetermined value.

20. The motor controller according to claim 17 , wherein the magnetization controller, when the decrease in the magnetization of the permanent magnet is detected by the demagnetization detector, increases the magnetization of the permanent magnet when an average of a q-axis current amplitude within a predetermined time period is equal to or less than a predetermine value.