Bi-stable, sub-commutated, direct-drive, sinusoidal motor controller for precision position control
An electric motor controller system for modulating requested motor torque via oscillating the instantaneous torque, including a bi-stable torque controller; a proportional-integral (PI) velocity controller a proportional-integral-differential (PID) position controller; and sinusoidal zero-velocity table mapping.
1. A method comprising:
modulating a requested motor torque via oscillating a requested instantaneous torque;
generating, by a bi-stable torque controller comprising a sinusoidal drive table having at least three phases, the requested instantaneous torque, wherein the requested instantaneous torque is based on the sinusoidal drive table; and
communicating, via a brushless electric motor, with a torque drive oscillating circuit;
wherein the brushless electric motor comprises: a rotor having three or more multi-turn coils, each multi-turn coil disposed about an associated armature of the rotor; and a stator having circumferentially distributed magnetic elements.
2. The method of claim 1 , further comprising:
drawing from a sinusoidal zero-velocity table mapping to energize a brushless motor phase through the stator of the brushless motor;
detecting a static condition; and
yielding a symmetrical three-phase sinusoidal drive table for the brushless motor.
3. A method comprising:
achieving sub-degree pointing accuracy of a brushless direct current (DC) motor;
communicating, via a proportional-integral (PI) velocity controller, with a proportional-integral-differential (PID) position controller;
communicating, via a bi-stable torque controller, with the PI velocity controller; and
reducing torque ripple via sinusoidal zero-velocity table mapping in communication with the bi-stable torque controller.
4. The method of claim 3 , wherein the brushless DC motor is sub-commutated greater than one hundred times within one electrical commutation cycle.
5. The method of claim 3 , further comprising:
outputting, via the proportional-integral (PI) velocity controller, a result based on a velocity bias and a feedback of the brushless DC motor velocity.
6. The method of claim 3 , further comprising:
outputting, via the proportional-integral-differential (PID) position controller, a result based on a pointing routine and an angle measurement feedback.
7. The method of claim 3 , further comprising:
adjusting, via the sinusoidal zero-velocity table mapping, θ AR electrical degrees to yield a consistent torque curve over all positions within the brushless DC motor.
8. The method of claim 4 , further comprising:
oscillating, by the bi-stable torque controller, about a request to yield a modulated torque value to average a total torque requested of the brushless DC motor.
9. The method of claim 5 , further comprising:
outputting, via the proportional-integral (PI) velocity controller, the result to the bi-stable torque controller.
10. The method of claim 5 , further comprising:
receiving, via the proportional-integral (PI) velocity controller, an input frequency of 5 kHz.
11. The method of claim 6 , further comprising:
sampling, via the proportional-integral-differential (PID) position controller, directly from an encoder.
12. The method of claim 6 , further comprising:
outputting, via the proportional-integral-differential (PID) position controller, the result to the proportional-integral (PI) velocity controller.
13. The method of claim 8 , further comprising:
detecting, via a current sensor, a current through the brushless DC motor.
14. The method of claim 8 , further comprising:
restricting, via the bi-stable torque controller, a change in torque to a small fraction of torque change per second.
15. The method of claim 8 , further comprising:
adjusting, via the bi-stable torque controller, a delta torque more positive than negative to achieve a gradually modulated torque value when a forward position is requested.
16. The method of claim 8 , further comprising:
drawing, via the bi-stable torque controller, values from the sinusoidal zero-velocity table mapping.
17. The method of claim 13 , further comprising:
receiving, via the bi-stable torque controller, feedback input through a slow varying filter measured from an input of the current sensor.
18. The method of claim 16 , further comprising:
using, via the sinusoidal zero-velocity table mapping, three phases simultaneously to reduce torque ripple.
19. The method of claim 16 , further comprising:
using, via the sinusoidal zero-velocity table mapping, at least four phases simultaneously to reduce torque ripple.