Brushless DC motor controller - Patent Review 5929577

Claims

We claim:

1. A DC motor controller for controlling a brushless DC motor having a plurality of windings sequentially energized by a plurality of electronically controlled switches connecting each of said windings to a negative terminal or a positive terminal of a DC voltage supply in response to a corresponding plurality of drive signals, said controller comprising:

a track and hold circuit for tracking the voltage across one of said windings during a first interval when at least another one of said windings is energized and for holding said tracked voltage during a second interval when said at least another one of said windings is de-energized and for a predetermined delay interval thereafter;

a zero crossing comparator for comparing said held voltage to a reference voltage to provide an output signal indicative of when the voltage across said winding crosses said reference voltage; and

a decoder responsive to said output signal of said zero crossing comparator for providing said plurality of drive signals.

2. The DC motor controller recited in claim 1 further comprising a control logic circuit responsive to said output signal of said zero crossing comparator for providing an input signal to said decoder.

3. The DC motor controller recited in claim 1 wherein said track and hold circuit comprises an electronically controlled switch connected in series with a resistor and a capacitor connected between said electronically controlled switch and a reference potential.

4. The DC motor controller recited in claim 1 wherein said plurality of electronically controlled switches comprises a plurality of pairs of switching transistors, each pair being associated with a respective one of said plurality of windings and including a high side switch connected to the positive terminal of said DC voltage supply and a low side switch connected to the negative terminal of said DC voltage supply, wherein an interconnection between each of said pairs of transistors is connected to a terminal of a respective winding.

5. A DC motor controller for controlling a brushless DC motor having a plurality of windings connected to a corresponding plurality of pairs of switching transistors, each pair having a common connection to a terminal of a corresponding one of said plurality of windings and including a high side switch connected to the positive terminal of a DC voltage supply and a low side switch connected to a negative terminal of said DC voltage supply, said switches operative to sequentially energize said plurality of windings by connecting each of said windings to the negative terminal or the positive terminal of the DC voltage supply in response to a corresponding plurality of drive signals, said controller comprising:

a track and hold circuit for tracking the voltage across one of said windings and holding said tracked voltage;

a zero crossing comparator for comparing said held voltage to a reference voltage to provide an output signal indicative of when the voltage across said winding crosses said reference voltage; and

a decoder responsive to said output signal of said zero crossing comparator for providing said plurality of drive signals such that the low side switch of the pair of switching transistors associated with a negatively energized winding is chopped when said tracked and held voltage is negative and the high side switch of the pair of switching transistors associated with a positively energized winding is chopped when said tracked and held voltage is positive.

6. The DC motor controller recited in claim 1 wherein said motor has a centertap terminal, said track and hold circuit further tracks the voltage at said centertap terminal and holds said tracked voltage, and said reference voltage is provided by said tracked and held centertap voltage.

7. A DC motor controller for controlling a brushless DC motor having a plurality of windings and a plurality of electronically controlled switches for sequentially energizing said plurality of windings by connecting each of said windings to a negative terminal or a positive terminal of a DC voltage supply in response to a corresponding plurality of drive signals, said controller comprising:

a track and hold circuit for tracking the voltage across one of said windings and holding said tracked voltage;

a zero crossing comparator for comparing said held voltage to a reference voltage to provide an output signal indicative of when the voltage across said winding crosses said reference voltage;

a decoder responsive to said output signal of said zero crossing comparator for providing said plurality of drive signals; and

a PWM circuit responsive to a motor parameter for generating a PWM signal coupled to said decoder and used by said decoder to chop said drive signals, said PWM circuit inhibiting said PWM signal for an interval prior to and during when said voltage across said winding crosses said reference voltage.

8. The DC motor controller recited in claim 7 wherein said motor parameter is motor speed.

9. A DC motor controller for controlling a brushless DC motor having a plurality of windings and a plurality of electronically controlled switches for sequentially energizing said plurality of windings by connecting each of said windings to a negative terminal or a positive terminal of a DC voltage supply in response to a corresponding plurality of drive signals, said controller comprising:

a track and hold circuit for tracking the voltage across one of said windings and holding said tracked voltage;

a zero crossing comparator for comparing said held voltage to a reference voltage to provide an output signal indicative of when the voltage across said winding crosses said reference voltage;

a decoder responsive to said output signal of said zero crossing comparator for providing said plurality of drive signals; and

an interpolation circuit for interpolating said tracked and held voltage.

10. A brushless DC motor controller for controlling a motor having a plurality of windings, wherein said motor is commutated by a plurality of switching circuits, each associated with a respective one of said plurality of windings and comprising a high side switch connected to a positive terminal of a voltage supply and a low side switch connected to a negative terminal of said voltage supply, wherein each of said switches is controlled by a respective drive signal, said controller comprising:

a back EMF sensing circuit for sensing the back EMF across a floating one of said plurality of windings; and

a decoder responsive to said sensed back EMF for generating said drive signals such that said high side switch associated with a positively energized winding is chopped when said sensed back EMF is positive and wherein said low side switch associated with a negatively energized winding is chopped when said sensed back EMF is negative.

11. The DC motor controller recited in claim 10 wherein said back EMF sensing circuit comprises a track and hold circuit for tracking the voltage across said floating winding and holding said tracked voltage; and

a zero crossing comparator for comparing said tracked and held voltage to a reference voltage, said zero crossing comparator providing an output signal indicative of when said back EMF across said floating winding crosses said reference voltage.

12. The DC motor controller recited in claim 11 wherein said motor has a centertap terminal, said track and hold circuit further tracks the voltage at said centertap terminal and holds said tracked voltage, and said reference voltage is provided by said tracked and held centertap voltage.

13. The DC motor controller recited in claim 11 wherein said tracked and held voltage is interpolated.

14. The DC motor controller recited in claim 10 further comprising a PWM circuit responsive to a motor parameter for generating a PWM signal coupled to said decoder, wherein said PWM signal is inhibited for an interval prior to and during when said voltage across said floating winding crosses said reference voltage.

15. The DC motor controller recited in claim 14 wherein said motor parameter is motor speed.

16. A DC motor controller for controlling a motor comprising a plurality of windings and a plurality of electronically controlled switches for sequentially energizing said plurality of windings in response to a corresponding plurality of drive signals, said controller comprising:

a rotor position sensing circuit for sensing when the voltage across one of said plurality of windings experiences a zero crossing by crossing a reference voltage level;

a motor parameter sensing circuit for sensing a parameter of said motor selected from the group consisting of: motor speed, motor torque, or motor acceleration;

a PWM circuit responsive to said sensed motor parameter for generating an error signal indicative of the difference between said sensed signal and a desired value for said motor parameter and for generating a PWM signal in response to said error signal, wherein said PWM signal is used to selectively chop said drive signals; and

a PWM disable circuit for disabling said PWM circuit prior to and during said zero crossing.

17. The DC motor controller recited in claim 16 wherein said rotor position sensing circuit comprises a track and hold circuit for tracking the voltage across said one of said plurality of windings and holding said voltage; and

a zero crossing comparator responsive to said tracked and held voltage and to a reference voltage for detecting said zero crossing.

18. The DC motor controller recited in claim 16 wherein said PWM disable circuit comprises a buffer amplifier coupled to a centertap terminal of said motor and providing a buffered output signal;

an offset voltage coupled to and summed with said output signal of said buffer amplifier; and

a gating comparator for comparing said sensed winding voltage to said summed voltage to provide a gating signal for inhibiting said PWM signal.

19. A method for sensing the position of a rotor relative to a stator having a plurality of windings associated therewith, said method comprising the steps of:

tracking the voltage across a selected one of said windings;

holding said winding voltage;

comparing said held voltage to a reference voltage to detect a crossing of said winding voltage with said reference voltage; and

interpolating said held winding voltage to smooth said voltage.

20. The method recited in claim 19 further comprising the steps of:

tracking the voltage at the centertap terminal of said motor;

holding said centertap voltage to provide said reference voltage; and

comparing said held centertap voltage to said held winding voltage to detect a crossing of said winding voltage with said centertap voltage.

21. A method for commutating a motor having a plurality of windings comprising the steps of:

sensing the back EMF across a floating one of said plurality of windings;

chopping a high side switch associated with a positively energized one of said plurality of windings when said sensed back EMF is positive; and

chopping a low side switch associated with a negatively energized one of said plurality of windings when said sensed back EMF is negative.

22. A method of sensing the position of a rotor relative to a stator having a plurality of windings in order to commutate said motor by sequentially energizing said plurality of windings through a switch network comprising a plurality of switches controlled by a corresponding plurality of drive signals, said method comprising the steps of:

sensing when the back EMF across a first one of said plurality of windings experiences a zero crossing by crossing a reference voltage level;

sensing a parameter of said motor selected from the group consisting of: motor speed, motor torque, or motor acceleration;

generating a PWM signal in response to the sensed motor parameter, said PWM signal having a duty cycle corresponding to a desired value for said motor parameter;

generating said drive signals in response to said PWM signal; and

inhibiting said PWM signal for an interval prior to and during said zero crossing.

23. The method recited in claim 22 wherein said PWM signal inhibiting step comprises the steps of summing the voltage at a centertap terminal of said motor with an offset voltage; and

comparing said summed voltage to said sensed winding voltage to provide a gating signal for inhibiting said PWM signal.

24. A DC motor controller for controlling a brushless DC motor having a plurality of windings and a plurality of pairs of electronically controlled switches for sequentially energizing said plurality of windings, each pair being associated with a respective one of said plurality of windings and including a high side switch connected to the positive terminal of a DC voltage supply and a low side switch connected to the negative terminal of said DC voltage supply, said controller comprising:

a track and hold circuit for tracking the voltage across one of said windings and holding said tracked voltage;

a zero crossing comparator for comparing said held voltage to a reference voltage to provide an output signal indicative of a zero crossing, when said held voltage crosses said reference voltage;

a control logic circuit responsive to said output signal of said zero crossing comparator for providing an plurality of position signals, each one corresponding to one of said plurality of windings;

a decoder responsive to said position signals for decoding said plurality of position signals to provide said plurality of drive signals such that the high side switch associated with a positively energized one of said plurality of windings is chopped when said held voltage is positive and wherein the low side switch associated with a negatively energized one of said plurality of windings is chopped when said held