PWM control of motor driver

• US 5,869,946 A
• Filed: 02/27/1997
• Issued: 02/09/1999
• Est. Priority Date: 02/27/1997
• Status: Expired due to Term

• Current Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Inventors: Carobolante, Francesco
• Primary Examiner(s): Shoop, Jr., William M.
• Assistant Examiner(s): Leykin, Rita
• Application Number:
  US08/814,932
• Time in Patent Office: 712 Days
• Field of Search: 318/254, 318/41, 318/597, 318/811, 363/41
• US Class Current: 318/811
• CPC Class Codes: H02P 2209/07 Trapezoidal waveform
• CPC Class Codes: H02P 6/085 in a bridge configuration
• CPC Class Codes: H02P 6/10 Arrangements for controlling torque ripple, e.g. providing reduced torque ripple

Abstract

Methods and apparatuses are provided for use in driving a multiple-phase brushless motor. The methods and apparatuses include generating a slewed phase control signal for each phase of the motor. The slewed phase control signals are substantially proportional to a speed control signal during non-transitioning periods, and are slewed from one state to the next state over time during transitioning periods. The transitioning periods being associated with a commutation point. The slewed phase control signals are used to generate pulse width modulated (PWM) driving signals, for each phase of the motor. Thus, the shape of the resulting PWM driving signal will include additional PWM pulses during the transitioning period that provide for a trapezoidal shaping of the current supplied to each of the phase coils in the motor. The result is that torque ripple is reduced because the overall current applied to the motor and the torque resulting therefrom will tend to be more constant during commutation.

Claims

1. A method for driving a multiple-phase motor, the method comprising:

generating a pair of slewed phase control signals that are opposite in polarity, the slewed phase control signals representing at least two operating states, wherein a first one of the operating states is directly proportional to a speed control signal, wherein the phase control signals switch between the operating states in response to a commutation event, the commutation event having a transitioning period associated therewith, wherein the phase control signals are slewed between the operating states during the transition period;

generating a pulse width modulated (PWM) phase driving signal for each of the slewed phase control signals; and

supplying the PWM phase driving signals to the motor.

2. The method as recited in claim 1 wherein the transitioning period begins prior to the commutation event and ends after the commutation event.

3. The method as recited in claim 2 wherein the transitioning period begins no sooner than about 30 electrical degrees prior to the commutation event, and ends no later than about 30 electrical degrees after the commutation event.

4. The method as recited in claim 1 wherein the transitioning period begins with the commutation event and ends after the commutation event.

5. The method as recited in claim 4 wherein the transitioning period ends no later than about 30 electrical degrees after the commutation event.

6. The method as recited in claim 1 wherein the transitioning period begins prior to the commutation event and ends with the commutation event.

7. The method as recited in claim 6 wherein the transitioning period begins no sooner than about 60°

prior to the commutation event.

8. The method as recited in claim 1 wherein the slewed phase control signals are substantially trapezoidal in shape.

9. The method as recited in claim 1 wherein the PWM phase driving signals are substantially trapezoidal in shape.

10. An apparatus for driving a multiple-phase motor, the apparatus comprising:

a slewing transitioner that generates a pair of pulse width modulated (PWM) phase driving signals, each PWM phase driving signal representing at least two operating states, wherein a first one of the operating states is directly proportional to a speed control signal, wherein the slewing transitioner gradually switches between the operating states during a transitioning period, and supplies the pair of PWM phase driving signals to the motor.

11. The apparatus as recited in claim 10 wherein the transitioning period begins prior to a commutation event and ends after the commutation event.

12. The apparatus as recited in claim 10 wherein the transitioning period begins with a commutation event and ends after the commutation event.

13. The apparatus as recited in claim 10 wherein the transitioning period begins prior to a commutation event and ends with the commutation event.

14. A driver circuit for use in a motor controller having a control circuit that outputs a speed control signal and a commutation control signal the driver circuit comprising:

a buffer stage coupled to the control circuit for receiving the speed control signal, the buffer stage generating at least one phase control signal that is proportional the received speed control signal;

a current switcher stage coupled to the buffer stage for receiving the phase control signal(s), and to the control circuit for receiving the commutation control signal, the current switcher stage generating a slewed phase control signal that is a function of the received phase control signal(s) and the received commutation control signal, wherein the current switcher stage comprises;

(a) a first current source coupled to the control circuit for receiving a first commutation control signal, the first current source generating a first current signal that is a function of the first commutation control signal, the first current signal being supplied to a compensation node within the current switcher stage;

(b) a second current source coupled to the control circuit for receiving a second commutation control signal, the second current source generating a second current signal that is a function of the second commutation control signal, the second current signal being supplied to the compensation node, wherein the second current is opposite in polarity to the first current with respect to the compensation node; and

(c) a slewing capacitor coupled to the compensation node and to a ground node;

a comparator stage coupled to the current switcher stage for receiving the slewed phase control signal, the comparator stage generating a pulse width modulated (PWM) phase control signal that is proportional to the slewed phase control signal; and

a driving stage coupled to the comparator stage for receiving the PWM phase control signal, the driving stage generating a driving signal that is proportional to the PWM phase control signal that is suitable for driving a motor.

15. The driver circuit as recited in claim 14, wherein the slewed phase control signal represents at least two operating states, wherein a first one of the operating states is directly proportional to a speed control signal, and is switched between the operating states in response to a commutation event, the commutation event having a transitioning period associated therewith wherein the phase control signal is slewed between the operating states during the transition period.

16. The driver circuit as recited in claim 14, wherein the comparator stage comprises a triangular waveform generator and a comparator, wherein the comparator is coupled to the triangular waveform generator for receiving a triangular waveform signal therefrom, and to the current switcher stage for receiving the slewed phase control signal, the comparator outputting the PWM phase control signal as a function of the triangular waveform signal and the slewed phase control signal.

17. The driver circuit as recited in claim 14, wherein the buffer stage comprises a decoupling device having an input node and an output node, wherein the input node is coupled to the control circuit for receiving the speed control signal, the output node is coupled to a compensation node in the current switcher stage for providing the phase control signal thereon, and the decoupling device provides a high impedance on the compensation node.

18. The driver circuit as recited in claim 17, wherein the decoupling device is a transistor having a control terminal as the input node and a second terminal as the output node.

19. A driver circuit for use in a motor controller having a control circuit that outputs a speed control signal and a commutation control signal, the driver circuit comprising:

a buffer stage coupled to the control circuit for receiving the speed control signal, the buffer stage generating at least one phase control signal that is proportional the received speed control signal and including;

(a) a first buffer coupled to the control circuit for receiving the speed control signal, the first buffer generating a first phase control signal, the first phase control signal being proportional to the speed control signal and

(b) a second buffer coupled the first buffer for receiving the first phase control signal, the second buffer generating a second phase control signal, the second phase control signal being proportional to the speed control signal inversely proportional to the first phase control signal with respect to a reference voltage signal;

a current switcher stage coupled to the buffer stage for receiving the phase control signal(s), and to the control circuit for receiving the commutation control signal, the current switcher stage generating a slewed phase control signal that is a function of the received phase control signal(s) and the received commutation control signal;

a comparator stage coupled to the current switcher stage for receiving the slewed phase control signal, the comparator stage generating a pulse width modulated (PWM) phase control signal that is proportional to the slewed phase control signal; and

a driving stage coupled to the comparator stage for receiving the PWM phase control signal, the driving stage generating a driving signal that is proportional to the PWM phase control signal that is suitable for driving a motor.

20. The driver circuit as recited in claim 19, wherein the second buffer is an inverting buffer having a first input coupled to the reference voltage signal and a second input coupled to receive the first phase control signal from the first buffer.

21. The driver circuit as recited in claim 19, wherein the slewed current switcher stage comprises a clamping diode coupled between the buffer stage and the compensation node.

22. A motor controller for use with a motor, the motor controller comprising:

a control circuit arranged to generate a speed control signal and a commutation control signal; and

a driver circuit comprising;

a buffer stage coupled to the control circuit for receiving the speed control signal, the buffer stage generating at least one phase control signal that is proportional the received speed control signal;

a current switcher stage coupled to the buffer stage for receiving the phase control signal(s), and to the control circuit for receiving the commutation control signal, the current switcher stage generating a slewed phase control signal that is a function of the received phase control signal(s) and the received commutation control signal, wherein the current switcher stage comprises;

(a) a first current source coupled to the control circuit for receiving a first commutation control signal, the first current source generating a first current signal that is a function of the first commutation control signal, the first current signal being supplied to a compensation node within the current switcher stage;

(b) a second current source coupled to the control circuit for receiving a second commutation control signal, the second current source generating a second current signal that is a function of the second commutation control signal, the second current signal being supplied to the compensation node, wherein the second current is opposite in polarity to the first current with respect to the compensation node; and

(c) a slewing capacitor coupled to the compensation node and to a ground node;

a comparator stage coupled to the current switcher stage for receiving the slewed phase control signal, the comparator stage generating a pulse width modulated (PWM) phase control signal that is proportional to the slewed phase control signal; and

a driving stage coupled to the comparator stage for receiving the PWM phase control signal, the driving stage generating a driving signal that is proportional to the PWM phase control signal that is suitable for driving a motor.

23. A disc drive comprising:

a motor; and

a motor controller comprising;

a control circuit arranged to generate a speed control signal and a commutation control signal; and

a driver circuit comprising;

a buffer stage coupled to the control circuit for receiving the speed control signal, the buffer stage generating at least one phase control signal that is proportional the received speed control signal;

a current switcher stage coupled to the buffer stage for receiving the phase control signal(s), and to the control circuit for receiving the commutation control signal, the current switcher stage generating a slewed phase control signal that is a function of the received phase control signal(s) and the received commutation control signal, wherein the current switcher stage comprises;

(a) a first current source coupled to the control circuit for receiving a first commutation control signal, the first current source generating a first current signal that is a function of the first commutation control signal, the first current signal being supplied to a compensation node within the current switcher stage;

(b) a second current source coupled to the control circuit for receiving a second commutation control signal, the second current source generating a second current signal that is a function of the second commutation control signal, the second current signal being supplied to the compensation node, wherein the second current is opposite in polarity to the first current with respect to the compensation node; and

(c) a slewing capacitor coupled to the compensation node and to a ground node;

a comparator stage coupled to the current switcher stage for receiving the slewed phase control signal, the comparator stage generating a pulse width modulated (PWM) phase control signal that is proportional to the slewed phase control signal; and

a driving stage coupled to the comparator stage for receiving the PWM phase control signal, the driving stage generating a driving signal that is proportional to the PWM phase control signal that is suitable for driving the motor.