Position-sensorless motor control device

1. A position-sensorless motor control device for controlling a motor, wherein

let an axis parallel to a magnetic flux produced by a permanent magnet forming a rotor of the motor be called a d axis,

let an axis estimated, for a purpose of control, to correspond to the d axis be called a γ axis, and

let an axis estimated to lead the γ axis by an electrical angle of 90 degrees be called a δ axis,

then the position-sensorless motor control device controls the motor such that an axis error between the d- and γ-axes is reduced,

the position-sensorless motor control device comprising:

a superposer that superposes, on a drive current with which the motor is driven, a superposed current having a different frequency than the drive current;

a superposed component extractor that extracts, from a motor current fed to the motor, γ-axis and δ-axis components of the superposed current; and

a controller that reduces the axis error by controlling the motor based on an arithmetic product of the γ-axis and δ-axis components of the superposed current.

2. The position-sensorless motor control device of claim 1 ,

wherein the superposer superposes the superposed current on the drive current by superposing a superposed voltage commensurate with the superposed current on a drive voltage that is applied to the motor to pass the drive current therethrough.

3. The position-sensorless motor control device of claim 2 ,

wherein a voltage vector locus of the superposed voltage on the γ-δ axes describes a figure symmetric about the γ or δ axis.

4. The position-sensorless motor control device of claim 2 ,

wherein a voltage vector locus of the superposed voltage on the γ-δ axes describes a perfect circle, or an ellipse having a minor or major axis on the γ axis, or a line segment on the γ or δ axis.

5. The position-sensorless motor control device of claim 2 , wherein

the motor is a non-salient-pole motor, and

the superposed voltage that the superposer superposes on the drive voltage is a voltage that causes a d-axis component of an inductance of the motor to vary by magnetic saturation attributable to a γ-axis component of the superposed current.

6. The position-sensorless motor control device of claim 1 ,

wherein the controller reduces the axis error by controlling the motor based on a direct-current component of the arithmetic product.

7. The position-sensorless motor control device of claim 6 ,

wherein the controller reduces the axis error by controlling the motor such that the direct-current component converges to zero.

8. A motor drive system comprising:

a motor;

an inverter for driving the motor; and

the position-sensorless motor control device of claim 1 , which controls the motor by controlling the inverter.

9. A position-sensorless motor control device for controlling a motor, wherein

let an axis parallel to a magnetic flux produced by a permanent magnet forming a rotor of the motor be called a d axis,

let an axis estimated, for a purpose of control, to correspond to the d axis be called a γ axis, and

let an axis estimated to lead the γ axis by an electrical angle of 90 degrees be called a δ axis,

then the position-sensorless motor control device controls the motor such that an axis error between the d- and γ-axes is reduced,

the position-sensorless motor control device comprising:

a superposer that superposes, on a drive current with which the motor is driven, a superposed current having a different frequency than the drive current;

a superposed component extractor that extracts γ-axis and δ-axis components of a superposed voltage that is applied to the motor to superpose the superposed current on the drive current; and

a controller that reduces the axis error by controlling the motor based on an arithmetic product of the extracted γ-axis and δ-axis components of the superposed voltage.

10. The position-sensorless motor control device of claim 9 ,

wherein the controller reduces the axis error by controlling the motor based on a direct-current component of the arithmetic product.

11. The position-sensorless motor control device of claim 10 ,

wherein the controller reduces the axis error by controlling the motor such that the direct-current component converges to zero.

12. The position-sensorless motor control device of claim 9 ,

wherein a current vector locus of the superposed current on the γ-δ axes describes a figure symmetric about the γ or δ axis.

13. The position-sensorless motor control device of claim 9 ,

wherein a current vector locus of the superposed current on the γ-δ axes describes a perfect circle, or an ellipse having a minor or major axis on the γ axis, or a line segment on the γ or δ axis.

14. The position-sensorless motor control device of claim 9 , wherein

the motor is a non-salient-pole motor, and

the superposed current that the superposer superposes on the drive current is a current that causes a d-axis component of an inductance of the motor to vary by magnetic saturation attributable to a γ-axis component of the superposed current.

15. A motor drive system comprising:

a motor;

an inverter for driving the motor; and

the position-sensorless motor control device of claim 9 , which controls the motor by controlling the inverter.