Methods and apparatus for three-phase motor control with error compensation

1. A method comprising:

operating a three-phase motor having a magnet with a number of pole-pairs and detecting zero crossings from a magnetic field sensing element proximate the magnet, wherein the zero crossings correspond to pole transitions for the pole-pairs;

determining drive angles corresponding to each of the zero crossings;

determining a reference angle from the drive angles;

sequentially positioning the motor to correspond to each one of the pole transitions and setting a drive angle to the reference angle;

examining a differential output signal generated from the magnetic field sensing element for each of the pole transitions;

adjusting a compensation level for the magnetic field sensing element for each of the pole transitions based on the differential output signal generated from the magnetic field sensing element for the respective pole transitions;

operating the motor and applying the compensation level for each of the pole transitions as the corresponding pole transition is proximate the magnetic field sensing element; and

further including providing the magnetic field sensing element as a Hall element.

2. The method according to claim 1 , further including examining the signal from the magnetic field sensing element using a three state comparator.

3. The method according to claim 1 , wherein compensation level for each of the pole transitions corresponds to an error in positioning of the magnetic field sensing element.

4. The method according to claim 1 , further including rotating the motor in clockwise and counterclockwise directions to reduce hysteresis error.

5. The method according to claim 1 , wherein the zero crossings correspond to S to N pole transitions.

6. The method according to claim 1 , further including taking an average of the driving angles to determine the reference angle.

7. The method according to claim 1 , further including using coarse and fine searching to determine the reference angle.

8. The method according to claim 1 , further including storing for each pole-pair transition a zero crossing angle, the reference angle, an error value, and a compensation value.

9. A system, comprising:

a motor controller for a three phase motor comprising:

a means for error compensation to operate the three-phase motor having a magnet with a number of pole-pairs and detecting zero crossings from a magnetic field sensing element proximate the magnet, wherein the zero crossings correspond to pole transitions for of the pole-pairs, to determine drive angles corresponding to each of the zero crossings, to determine the reference angle from the drive angles, to sequentially position the motor to correspond to each one of the pole transitions and setting a drive angle to the reference angle, to examining a differential output signal generated from the magnetic field sensing element for each of the pole transitions; to adjust a compensation level for the magnetic field sensing element for each of the pole transitions based on the differential output signal generated from the magnetic field sensing element for the respective pole transitions; and to operate the motor and applying the compensation level for each of the pole transitions as the corresponding pole transition is proximate the magnetic field sensing element, wherein the magnetic field sensing element comprises a Hall element.

10. The system according to claim 9 , wherein the means for error compensation is further configured to examine the signal from the magnetic field sensing element using a three state comparator.

11. The system according to claim 9 , wherein compensation level for each of the pole transitions corresponds to an error in positioning of the magnetic field sensing element.

12. The system according to claim 9 , wherein the means for error compensation is further configured to rotate the motor in clockwise and counterclockwise directions to reduce hysteresis error.

13. The system according to claim 9 , wherein the zero crossings correspond to S to N pole transitions.

14. The system according to claim 9 , wherein the means for error compensation is further configured to take an average of the driving angles to determine the reference angle.

15. The system according to claim 9 , wherein the means for error compensation is further configured to use coarse and fine searching to determine the reference angle.

16. An article, comprising:

a non-transitory storage medium having stored instructions that enable a machine to:

operate a three-phase motor having a magnet with a number of pole-pairs and detecting zero crossings from a magnetic field sensing element proximate the magnet, wherein the zero crossings correspond to pole transitions for of the pole-pairs;

determine drive angles corresponding to each of the zero crossings;

determine a reference angle from the drive angles;

sequentially position the motor to correspond to each one of the pole transitions and setting a drive angle to the reference angle;

examine a differential output signal generated from the magnetic field sensing element for each of the pole transitions;

adjust a compensation level for the magnetic field sensing element for each of the pole transitions based on the differential output signal generated from the magnetic field sensing element for the respective pole transitions; and

operate the motor and applying the compensation level for each of the pole transitions as the corresponding pole transition is proximate the magnetic field sensing element, wherein the magnetic field sensing element comprises a Hall element.

17. The article according to claim 16 , further including instructions to examine the signal from the magnetic field sensing element using a three state comparator.

18. The article according to claim 16 , wherein compensation level for each of the pole transitions corresponds to an error in positioning of the magnetic field sensing element.

19. The article according to claim 16 , further including instructions to use coarse and fine searching to determine the reference angle.