Dual-controller system for a sensorless brushless motor control

Patent metadata

Field	Value
Publication number	US-11303235-B2
Application number	US-202016853140-A
Country	US
Kind code	B2
Filing date	Apr 20, 2020
Priority date	Apr 25, 2019
Publication date	Apr 12, 2022
Grant date	Apr 12, 2022

Abstract

A power tool is provided including a brushless motor having a stator defining a plurality of phases and a rotor. A power unit is provided including power switches operable to deliver power to the motor. A primary controller is interfaced with the power unit to output drive signals to drive the phases of the motor over a series of sectors of the rotor rotation. The primary controller measures a back-electromotive force voltage of the motor and transitions motor commutation from the present sector to the next sector based in relation to the back-EMF voltage. A second controller is provided to receive at least one of the drive signals, calculate a speed and/or direction of rotation of the motor from the drive signals, and take corrective action to cut off supply of power to the motor if it detects an overspeed condition or incorrect direction of rotation.

First claim

The invention claimed is:

1. A power tool comprising:
a brushless motor having a stator defining a plurality of phases, a rotor rotatable relative to the stator, and a plurality of power terminals electrically connected to the plurality of phases;
a power unit having a plurality of power switches connected electrically between a power source and the plurality of motor terminals and operable to deliver power to the motor;
a primary controller interfaced with the power unit to output a plurality of drive signals to the plurality of motor switches to drive the plurality of phases of the motor over a plurality of sectors of the rotor rotation, the primary controller being configured to measure a back-electromotive force (back-EMF) voltage of the motor on an open phase of the plurality of phases and to transition commutation of the motor from a present sector of the plurality of sectors to a next sector of the plurality of sectors based in relation to the back-EMF voltage; and
a secondary controller configured to receive at least one drive signal of the plurality of drive signals, calculate a speed of the motor based on a frequency of a voltage signal on the at least one drive signal, and take corrective action to cut off supply of power to the brushless motor if the calculated speed exceeds a target speed or a speed threshold.

2. The power tool of claim 1 , wherein the primary controller comprises a gate driver unit configured to output the plurality of drive signals at voltage levels suitable for driving the plurality of power switches, wherein the secondary controller receives the plurality of drive signals outputted from the gate driver unit.

3. The power tool of claim 2 , wherein the corrective action by the secondary controller comprises disabling the gate driver unit.

4. The power tool of claim 1 , wherein the secondary controller is configured to receive three drive signals of the plurality of drive signals, generate two analog signals having substantially sinusoidal voltage waveform from the three drive signals, and detect the speed of the motor and a direction of rotation of the motor based on the two analog signals.

5. The power tool of claim 4 , wherein the secondary controller detects a zero-crossing of the two analog signals.

6. The power tool of claim 1 , wherein the secondary controller is configured to receive two drive signals of the plurality of drive signals, determine direction of rotation of the motor based on a sequence of voltage signals on the two drive signals, and take corrective action to cut off supply of power to the brushless motor if the direction of rotation does not match a target direction of rotation.

7. The power tool of claim 6 , wherein the secondary controller takes the corrective action if leading edges of the two drive signals or trailing edges of the two drive signals are not detected in a correct sequence.

8. The power tool of claim 6 , wherein a conduction band corresponding to an angle within which each of the plurality of phases of the motor is commutated is 120 degrees and the secondary controller takes the corrective action if a leading edge of one of the drive signals associated with a present phase does not occur substantially simultaneously with a trailing edge of the other drive signal associated with a previous phase.

9. The power tool of claim 6 , wherein a conduction band corresponding to an angle within which one of the plurality of phases of the motor is commutated is set to a value greater than 120 degrees and the secondary controller takes the corrective action if a leading edge of one of the drive signals associated with a present phase does not occur prior to a trailing edge of the other drive signal associated with a previous phase.

10. The power tool of claim 1 , wherein the two drive signals are coupled to gates of low-side power switches of the plurality of power switches.

11. The power tool of claim 1 , wherein the secondary controller is configured to monitor leading or trailing edges of the at least one drive signal, and compare at least two of the leading or trailing edges to determine the speed of the motor if a time difference between the at least two of the leading or trailing edges is greater than a time threshold.

12. The power tool of claim 11 , wherein the two drive signals are coupled to gates of low-side power switches of the plurality of power switches and the primary controller drives the plurality of phases of the motor with active freewheeling.

13. The power tool of claim 1 , further comprising a trigger switch engageable by a user to activate the power tool, wherein the secondary controller is configured to continue to assert the corrective action until the trigger switch is disengaged and reengaged by the user.

14. A power tool comprising:
a brushless motor having a stator defining a plurality of phases, a rotor rotatable relative to the stator, and a plurality of power terminals electrically connected to the plurality of phases;
a power unit having a plurality of power switches connected electrically between a power source and the plurality of motor terminals and operable to deliver power to the motor;
a primary controller interfaced with the power unit to output a plurality of drive signals to the plurality of motor switches to drive the plurality of phases of the motor over a plurality of sectors of the rotor rotation, the primary controller being configured to measure a back-electromotive force (back-EMF) voltage of the motor on an open phase of the plurality of phases and to transition commutation of the motor from a present sector of the plurality of sectors to a next sector of the plurality of sectors based in relation to the back-EMF voltage; and
a secondary controller configured to receive at least two drive signal of the plurality of drive signals, determine direction of rotation of the motor based on a sequence of voltage signals on the two drive signals, and take corrective action to cut off supply of power to the brushless motor if the direction of rotation does not match a target direction of rotation.

15. The power tool of claim 14 , wherein the secondary controller takes the corrective action if leading edges of the two drive signals or trailing edges of the two drive signals are not detected in a correct sequence.

16. The power tool of claim 14 , wherein the two drive signals are coupled to gates of low-side power switches of the plurality of power switches.

Assignees

• Black & Decker Inc

Inventors

• Thrush Jason
• Besack Gregory
• Kowalski Michael J
• Vanko John C

Classifications

• H02P29/028

  the motor continuing operation despite the fault condition, e.g. eliminating, compensating for or remedying the fault · CPC title

• H02P6/185

  using inductance sensing, e.g. pulse excitation · CPC title

• H02P23/03

  specially adapted for very low speeds · CPC title

• H02P6/15

  Controlling commutation time · CPC title

• H02P2209/07

  Trapezoidal waveform · CPC title