Determining motor position with complementary drive and detect and slight move
Methods and apparatus for determining a position of a rotor in a three-phase motor by determining first and second ones of sectors in which a first one of the magnetic poles of the rotor may be positioned by respectively driving phase pairs complementary signals and examining a voltage of a floating one of the phases. Embodiments can include applying torque to the motor by driving at least one phase pair with respective signals aligned in phase and unequal duty cycles to move the rotor a given amount from the rotor position in the first or second ones of the sectors for determining the position of the rotor.
1. A method of determining a position of a rotor in a three-phase motor having phase A, phase B, and phase C, comprising:
determining first and second ones of sectors in which a first one of the magnetic poles of the rotor may be positioned, wherein the first and second ones of the sectors are oppositely located, by respectively driving phase pairs A-B, A-C, and B-C with complementary signals and examining a voltage of a floating one of the phases; and
applying torque to the motor by driving at least one phase pair with respective signals aligned in phase and unequal duty cycles to move the rotor a given amount from the rotor position in the first or second ones of the sectors for determining the position of the rotor.
2. The method according to claim 1 , further including moving the rotor the given amount by determining when the voltage of the floating one of the phases is less than a threshold.
3. The method according to claim 1 , further including driving a phase pair with complementary signals to confirm the rotor position after the rotor moves the given amount.
4. The method according to claim 1 , wherein the motor comprises a drive brushless DC (BLDC) motor.
5. The method according to claim 1 , wherein the sectors comprise twelve sectors.
6. The method according to claim 1 , wherein the first and second ones of the sectors span about thirty degrees.
7. The method according to claim 1 , further including driving phase pairs A-B, A-C, and B-C with the complementary signals having about fifty percent duty cycle.
8. The method according to claim 1 , further encoding outputs of comparisons of the respective floating voltages and a voltage threshold during the driving of phase pairs A-B, A-C, and B-C with complementary signals.
9. The method according to claim 1 , wherein the given amount corresponds to about 45 degrees.
10. The method according to claim 1 , wherein the rotor position is determined within thirty degrees.
11. The method according to claim 1 , further including moving the rotor clockwise the given amount from the rotor position in the first one of the sectors or moving the rotor counter clockwise the given amount from the rotor position in the second one of the sectors.
12. A system for determining position of a rotor of a three-phase motor, comprising:
a first module to generate drive signals for the three-phase motor;
a second module configured to determine first and second ones of sectors in which a first one of the magnetic poles of the rotor may be positioned, wherein the first and second ones of the sectors are oppositely located, by driving phase pairs A-B, A-C, and B-C with complementary signals and examining a voltage of a floating one of the phases; and
a third module configured to apply torque to the motor by driving at least one phase pair with respective signals aligned in phase and unequal duty cycles to move the rotor a given amount from the rotor position in the first or second ones of the sectors for determining the position of the rotor.
13. The system according to claim 12 , wherein the system is further configured to move the rotor the given amount by determining when the voltage of the floating one of the phases is less than a threshold.
14. The system according to claim 12 , wherein the system is further configured to drive a phase pair with complementary signals to confirm the rotor position after the rotor moves the given amount.
15. The system according to claim 12 , wherein the motor comprises a drive brushless DC (BLDC) motor.
16. The system according to claim 12 , wherein the sectors comprise twelve sectors.
17. The system according to claim 12 , wherein the first and second ones of the sectors span about thirty degrees.
18. The system according to claim 12 , wherein the system is further configured to encode outputs of comparisons of the respective floating voltages and a voltage threshold during the driving of phase pairs A-B, A-C, and B-C with complementary signals.
19. The system according to claim 12 , wherein the given amount corresponds to about 45 degrees.
20. The system according to claim 12 , wherein the rotor position is determined within thirty degrees.
21. The system according to claim 12 , wherein the system is further configured to move the rotor clockwise the given amount from the rotor position in the first one of the sectors or moving the rotor counter clockwise the given amount from the rotor position in the second one of the sectors.