Brushless DC motor sensor control system and method

• US 6,538,403 B2
• Filed: 12/20/2000
• Issued: 03/25/2003
• Est. Priority Date: 01/07/2000
• Status: Expired due to Fees

• Current Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Original Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Inventors: Gorti, Bhanuprasad V., Walter, Richard T.
• Primary Examiner(s): Leykin, Rita
• Application Number:
  US09/742,839
• Publication Number:
  US 20010043806A1
• Time in Patent Office: 825 Days
• Field of Search: 318/254, 318/138, 318/439, 310/40.R, 310/42, 310/68.R
• US Class Current: 318/400.11
• CPC Class Codes: H02K 29/08 using magnetic effect devices, e.g. Hall-plates, magneto-resistors H02K29/12 takes precedence
• CPC Class Codes: H02K 3/47 Air-gap windings, i.e. iron-free windings
• CPC Class Codes: H02P 6/16 Circuit arrangements for detecting position
• CPC Class Codes: H02P 6/21 Open loop start
• CPC Class Codes: H02P 6/22 in a selected direction of rotation

Abstract

A system and method for controlling a brushless DC motor (58) is provided. The motor (58) includes a rotor (72) and a stator (96) having at least three phases. The rotor (72) is magnetically coupled to and moveable by the stator (96) when the coils (94) are appropriately energized. Each of the coils (94) is characterized by a corresponding voltage waveform. No more than two position sensors (122) are provided for sensing the position of the rotor (72) during a start-up mode. Each position sensor (122) has an associated position sensor signal. The position sensors (122) are aligned to sense the rotor position such that each position sensor signal indicates a zero torque point corresponding to a phase voltage waveform. The position of the rotor (72) is sensed such that the position sensor signals indicate the start-up operating state of the motor (58). During a first ambiguous start-up state, two predetermined coils (94) are alternately energized. During a defined start-up operating state, one predetermined coil (94) is energized.

Claims

1. A method for controlling a brushless DC motor including a rotor and a stator having at least three phases, the rotor being magnetically coupled to and moveable by the stator when the phases are appropriately energized, each of the phases being characterized by a corresponding voltage waveform, comprising the steps of:

providing no more than two position sensors for sensing a rotor position during a start-up mode, each position sensor having an associated position sensor signal;

aligning the position sensors to sense the rotor position such that each position sensor signal indicates a zero torque point corresponding to a phase voltage waveform;

sensing the position of the rotor such that the position sensor signals indicate a start-up operating state;

during a first ambiguous start-up state;

alternately energizing two predetermined phases; and

during a defined start-up operating state;

energizing one predetermined phase.

2. The method of claim 1 further including the step of determining a rotor speed.

3. The method of claim 2 further including the step of selecting a steady-state mode when the rotor speed exceeds a predetermined speed.

4. The method of claim 3 further including the step of executing phase-lock loop operation during steady-state mode.

5. The method of claim 1 wherein two position sensors are provided for sensing the rotor position during the start-up mode.

6. The method of claim 5 wherein each of the position sensors is aligned with a voltage-to-voltage waveform.

7. The method of claim 6 wherein the step of alternately energizing includes pulsing the phase for a predetermined pulse duration.

8. The method of claim 7 wherein the pulse duration is fixed.

9. The method of claim 8 further including the step of determining a rotor speed.

10. The method of claim 9 further including the step of selecting a steady-state mode when the rotor speed exceeds a predetermined speed.

11. The method of claim 10 further including the step of generating a timed pulse to stop the rotor in a predetermined position.

12. The method of claim 1 wherein one position sensor is provided for sensing the rotor position during the start-up mode.

13. The method of claim 12 wherein the position sensor is aligned with a voltage-to-neutral waveform.

14. The method of claim 13 wherein the step of alternately energizing includes pulsing the phase for a predetermined pulse duration.

15. The method of claim 14 wherein the pulse duration is fixed.

16. The method of claim 15 further including the step of determining a rotor speed.

17. The method of claim 16 further including the step of selecting a steady-state mode when the rotor speed exceeds a predetermined speed.

18. A method for controlling a brushless DC motor including a rotor and a stator having at least three phases, the rotor being magnetically coupled to and moveable by the stator when the phases are appropriately energized, each of the phases being characterized by a corresponding voltage waveform, comprising the steps of:

providing two position sensors for sensing a rotor position during a start-up mode, each position sensor having an associated position sensor signal;

aligning the position sensors to sense the rotor position such that each position sensor signal indicates a zero torque point corresponding to a phase voltage waveform;

determining a rotor speed;

selecting an operating mode based on the rotor speed, the operating mode being a start-up mode for rotor speed up to about a predetermined speed and steady-state mode for rotor speed more than the predetermined speed;

during the start-up mode;

sensing the position of the rotor such that the position sensor signals indicate a start-up operating state;

during a first ambiguous start-up state;

alternately energizing two predetermined phases; and

during a defined start-up state;

energizing one predetermined phase.

19. The method of claim 18 further including the step of selecting a steady-state mode when the rotor speed exceeds a predetermined speed.

20. The method of claim 19 wherein each of the position sensors is aligned with a voltage-to-voltage waveform.

21. The method of claim 19 wherein the step of alternately energizing includes pulsing the phase for a predetermined pulse duration.

22. The method of claim 21 wherein the pulse duration is selectable.

23. A cordless power tool, comprising:

a brushless DC motor for converting electrical energy to mechanical energy, including;

a rotor and a stator having at least three coils configured in a three-phase configuration, the rotor being magnetically coupled to and moveable by the stator when the coils are appropriately energized, each of the phases being characterized by a corresponding voltage waveform

a position sensor assembly for sensing the positional relationship between the rotor and the coils, the position sensor assembly having no more than two position sensors for sensing a rotor position during a start-up mode, each position sensor having an associated position sensor signal, the position sensors being aligned to sense the rotor position such that each position sensor signal indicates a zero torque point corresponding to a phase voltage waveform; and

a controller, responsive to said position sensor assembly, for controlling the supply of power to the brushless DC motor, including;

a commutation module for energizing the coils;

a control module coupled to the commutation module for controlling the application of energy to the coils, including;

a speed calculator for determining a rotor speed;

a mode selector, in response to the rotor speed, for selecting an operating mode for energizing the coils;

a switch pulser coupled to the mode selector, activable during a start-up mode, to alternately energize two predetermined phases; and

a power module for supplying electrical energy to the brushless DC motor;

a tool interface for interfacing the DC motor with a tool; and

a housing for enclosing the power module, controller and DC motor.

24. The cordless power tool of claim 23 wherein the control module further includes a timed pulse generator coupled to the mode selector, activable during a stop mode, to generate a timed pulse to stop the rotor in a predetermined position.

25. The cordless power tool of claim 23 wherein each of the position sensors is aligned with a voltage-to-voltage waveform.

26. The cordless power tool of claim 23 wherein the switch pulser alternately energizes each of the two predetermined phases for a predetermined pulse duration.

27. The cordless power tool of claim 26 wherein the pulse duration is selectable.

28. The cordless power tool of claim 23 wherein the control module further includes a phase lock loop coupled to the mode selector, activable during a steady-state mode, to execute phase-lock operation.

29. The cordless power tool of claim 23 wherein the stator further includes at least one sensor channel in magnetic field communication with the position sensor assembly.

30. A brushless DC motor, comprising;

a rotor assembly including a rotatable shaft and a permanent magnet affixed to the shaft, said permanent magnet for generating a magnetic field;

a winding form enclosing the rotor assembly;

a plurality of coils wound upon the winding form to produce a magnetic field for applying a torque to the rotor assembly, said coils being connected in a three phase configuration having a positional relationship with the permanent magnet;

a stator stack made of a stator magnetic material for providing a magnetic flux return path for the magnetic field of the permanent magnet, the stator stack including a sensor channel to direct leakage flux from the permanent magnet to an associated position sensor;

a position sensor system for sensing the positional relationship that the coils have with the permanent magnet, the position sensor system including at least one position sensor in magnetic flux communication with the sensor channel; and

a controller coupled to the position sensor for controlling the application of a power source to the coils in response to the positional relationship of the coils and the permanent magnet.

31. The brushless DC motor of claim 30 wherein the stator stack includes no more than three sensor channels.

32. The brushless DC motor of claim 31 wherein the position sensor is a Hall cell.