DC motor control over wide dynamic range
Various examples are provided for brushless direct current (DC) motor control over a wide dynamic range. In one example, among others, a system including a power drive coupled to a DC motor and a MCU configured to control commutation of the DC motor based upon shaft speed of the DC motor, where the MCU transitions between a motion-based commutation mode and a time-based commutation mode in response to a comparison of the shaft speed with a predefined threshold. In another example, a method includes commutating a DC motor in response to a transition in rotor position of the DC motor and transitioning from a motion-based commutation mode to a time-based commutation mode in response to a comparison of shaft speed of the DC motor to a predefined threshold.
1. A system for control of direct current (DC) motors, comprising:
a power drive coupled to a brushless DC motor; and
a micro control unit (MCU) configured to control commutation of the brushless DC motor based upon shaft speed of the brushless DC motor, where the MCU transitions between a motion-based commutation mode and a time-based commutation mode in response to a comparison of the shaft speed with a predefined threshold, where in the time-based commutation mode a rotor position is determined in response to expiration of a timer having a period corresponding to a desired shaft speed and current supplied to the brushless DC motor is adjusted based upon the rotor position of the brushless DC motor determined at the expiration of the timer.
2. The system of claim 1 , wherein the time-based commutation mode commutates the brushless DC motor in response to expiration of the timer having the period corresponding to the desired shaft speed.
3. The system of claim 1 , wherein the rotor position is based upon signals from Hall Effect sensors of the brushless DC motor.
4. The system of claim 3 , further comprising an input isolation boundary configured to isolate outputs of the Hall Effect sensors from the MCU.
5. The system of claim 1 , wherein the current supplied to the brushless DC motor is increased in response to an insufficient change in the rotor position.
6. The system of claim 1 , further comprising an output isolation boundary configured to isolate outputs of the MCU from gate drive circuitry of the power drive.
7. The system of claim 1 , further comprising a current limiter configured to provide an indication to the MCU that load current exceeds a predefined limit.
8. The system of claim 7 , wherein the current limiter comprises a selectable voltage divider to set the predefined limit.
9. The system of claim 1 , wherein the motion-based commutation mode commutates the brushless DC motor in response to a predefined change in rotor position of the brushless DC motor.
10. The system of claim 9 , wherein the commutation of the brushless DC motor is in response to a transition in a signal from a Hall Effect sensor of the brushless DC motor.
11. The system of claim 1 , wherein the system is further configured to control commutation of a brushed DC motor when coupled to the power drive.
12. A system for control of direct current (DC) motors, comprising:
a power drive coupled to a brushless DC motor;
a micro control unit (MCU) configured to control commutation of the brushless DC motor based upon shaft speed of the brushless DC motor, where the MCU transitions between a motion-based commutation mode and a time-based commutation mode in response to a comparison of the shaft speed with a predefined threshold; and
a watchdog timer configured to initiate a motor stall protocol if the watchdog timer expires before a next Hall Effect signal transition occurs, where the watchdog timer is reset at a Hall Effect signal transition preceding the next Hall Effect signal transition, the Hall Effect signals from at least one Hall Effect sensor of the brushless DC motor.
13. The system of claim 12 , wherein the time-based commutation mode commutates the brushless DC motor in response to expiration of a commutation timer having a period corresponding to a desired shaft speed.
14. The system of claim 12 , wherein the motion-based commutation mode commutates the brushless DC motor in response to a predefined change in rotor position of the brushless DC motor, wherein the predefined change in rotor position is based upon signals from the at least one Hall Effect sensor of the brushless DC motor.
15. A method, comprising:
commutating, in a motion-based commutation mode, a brushless DC motor by switching a power drive coupled to the brushless DC motor in response to a transition in rotor position of the brushless DC motor;
comparing a shaft speed of the brushless DC motor to a predefined threshold;
transitioning to a time-based commutation mode in response to the comparison;
determining a rotor position in response to expiration of a commutation timer having a timeout period corresponding to a desired shaft speed; and
adjusting current supplied to the DC motor during commutation based upon the rotor position of the brushless DC motor.
16. The method of claim 15 , further comprising determining the shaft speed based upon signals from Hall Effect sensors of the brushless DC motor.
17. The method of claim 15 , further comprising initiating the commutation timer in response to the transition to the time-based commutation mode.
18. The method of claim 15 , further comprising commutating the brushless DC motor by switching the power drive in response to timeout of the commutation timer.
19. The method of claim 15 , further comprising transitioning from the time-based commutation mode to the motion-based commutation mode in response to a subsequent comparison of shaft speed to the predefined threshold.
20. The method of claim 15 , further comprising transitioning from the time-based commutation mode to the motion-based commutation mode in response to a subsequent comparison of shaft speed to a second predefined threshold.