MUTUAL INDUCTANCE VOLTAGE OFFSET COMPENSATION FOR BRUSHLESS DC SENSORLESS MOTORS

• US 20180159451A1
• Filed: 02/01/2018
• Published: 06/07/2018
• Est. Priority Date: 11/10/2015
• Status: Active Grant

• Current Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: Boscolo Berto, Michele, Vittoni, Siro
• Granted Patent: US 10,447,187 B2
• Time in Patent Office: Days
• CPC Class Codes: H02P 6/157 wherein the commutation is function of electro-magnetic force [EMF]
• CPC Class Codes: H02P 6/182 using back-emf in windings
• CPC Class Codes: H02P 6/185 using inductance sensing, e.g. pulse excitation

Abstract

A control circuit controls the operation of a brushless DC (BLDC) sensorless motor having a first terminal connected to a first winding, a second terminal connected to a second winding and a third terminal connected to a third winding. A driver circuit applies drive signals to the first and second terminals and places the third terminal in a high-impedance state. The drive signals include first drive signals at a first current amplitude and second drive signals at a second current amplitude different from the first current amplitude. A differencing circuit senses a first mutual inductance voltage at the third terminal in response to the first drive signals and senses a second mutual inductance voltage at the third terminal in response to the second drive signals. The differencing circuit further determines a difference between the first and second mutual inductance voltages and produces a difference signal that is used for zero-crossing detection and rotor position sensing.

Claims

1. A control circuit for controlling operation of a brushless DC (BLDC) sensorless motor having a first terminal connected to a first winding, a second terminal connected to a second winding and a third terminal connected to a third winding, comprising:

a drive control circuit configured to control the generation of drive signals to the first and second terminals and place the third terminal in a high-impedance state;

wherein the drive signals include first drive signals at a first current magnitude and second drive signals at a second current magnitude different from the first current magnitude; and

a differencing circuit comprising;

an amplifier circuit configured to sense a first mutual inductance voltage at the third terminal in response to the first drive signals and sense a second mutual inductance voltage at the third terminal in response to the second drive signals;

a sample and hold circuit coupled to an output of the amplifier circuit to save one of the first and second mutual inductance voltages; and

a comparator circuit having a first input coupled to an output of the sample and hold circuit to receive the saved one of the first and second mutual inductance voltages and a second input coupled to an output of the amplifier circuit to receive the another one of the first and second mutual inductance voltages, said comparator circuit configured to determine a difference between the first and second mutual inductance voltages and produce a difference signal.

2. The control circuit of claim 1,

wherein said amplifier circuit has a first input coupled to the third terminal and a second input coupled to receive a reference signal;

and

wherein the motor further comprises a center tap for windings of the motor, said reference signal comprising a voltage at the center tap.

3. The control circuit of claim 1,

wherein said amplifier circuit has a first input coupled to the third terminal and a second input coupled to receive a reference signal;

and

further comprising a virtual center tap circuit configured to provide a virtual center tap of the motor, said reference signal comprising a voltage at the virtual center tap.

4. The control circuit of claim 1, further comprising a zero-crossing detection circuit configured to receive the difference signal and detect a zero-crossing condition of the difference signal.

5. The control circuit of claim 4, wherein the drive control circuit comprises a logic circuit configured to process the detected zero-crossing condition and determine a position of the rotor.

6. The control circuit of claim 4, wherein the zero-crossing detection circuit comprises a comparator circuit having a first input configured to receive the difference signal and a second input configured to receive a null reference signal.

7. The control circuit of claim 1, wherein a change in sign of said difference signal indicates occurrence of a zero-crossing event.

8. The control circuit of claim 7, wherein the drive control circuit comprises a logic circuit configured to process the zero-crossing event and determine a position of the rotor.

9. A control circuit for controlling operation of a brushless DC (BLDC) sensorless motor having a first terminal connected to a first winding, a second terminal connected to a second winding and a third terminal connected to a third winding, comprising:

a drive control circuit configured to control the generation of drive signals to the first and second terminals and place the third terminal in a high-impedance state;

wherein the drive signals include first drive signals at a first current magnitude and second drive signals at a second current magnitude different from the first current magnitude; and

a differencing circuit comprising;

an amplifier circuit configured to sense the first and second mutual inductance voltages;

an analog to digital converter circuit having an input coupled to an output of the amplifier circuit, said analog to digital converter circuit configured to convert the sensed first and second mutual inductance voltages to digital values; and

wherein said drive control circuit comprises a logic circuit configured to process the digital values to produce a difference signal indicative of a difference between the first and second mutual inductance voltages.

10. The control circuit of claim 9,

wherein said amplifier circuit has a first input coupled to the third terminal and a second input coupled to receive a reference signal;

and

wherein the motor further comprises a center tap for windings of the motor, said reference signal comprising a voltage at the center tap.

11. The control circuit of claim 9,

wherein said amplifier circuit has a first input coupled to the third terminal and a second input coupled to receive a reference signal;

and

further comprising a virtual center tap circuit configured to provide a virtual center tap of the motor, said reference signal comprising a voltage at the virtual center tap.

12. The control circuit of claim 9, further comprising a zero-crossing detection circuit configured to receive the difference signal and detect a zero-crossing condition of the difference signal.

13. The control circuit of claim 12, wherein the drive control circuit comprises a logic circuit configured to process the detected zero-crossing condition and determine a position of the rotor.

14. The control circuit of claim 12, wherein the zero-crossing detection circuit comprises a comparator circuit having a first input configured to receive the difference signal and a second input configured to receive a null reference signal.

15. The control circuit of claim 9, wherein a change in sign of said difference signal indicates occurrence of a zero-crossing event.

16. The control circuit of claim 15, wherein the drive control circuit comprises a logic circuit configured to process the zero-crossing event and determine a position of the rotor.

17. A control circuit for controlling operation of a brushless DC (BLDC) sensorless motor having a first terminal connected to a first winding, a second terminal connected to a second winding and a third terminal connected to a third winding, comprising:

a drive control circuit configured to control the generation of drive signals to the first and second terminals and place the third terminal in a high-impedance state;

wherein the drive signals include first drive signals at a first current magnitude and second drive signals at a second current magnitude different from the first current magnitude; and

a differencing circuit comprising;

an analog to digital converter circuit having a first input coupled to the third terminal and a second input coupled to a reference signal, said analog to digital converter circuit configured to convert the voltages at the third terminal and reference signal to digital values; and

wherein the drive control circuit comprises a logic circuit configured to process the digital values to produce a difference signal.

18. The control circuit of claim 17, wherein the motor further comprises a center tap for windings of the motor, said reference signal comprising a voltage at the center tap.

19. The control circuit of claim 17, further comprising a virtual center tap circuit configured to provide a virtual center tap of the motor, said reference signal comprising a voltage at the virtual center tap.

20. The control circuit of claim 17, further comprising a zero-crossing detection circuit configured to receive the difference signal and detect a zero-crossing condition of the difference signal.

21. The control circuit of claim 20, wherein the drive control circuit comprises a logic circuit configured to process the detected zero-crossing condition and determine a position of the rotor.

22. The control circuit of claim 20, wherein the zero-crossing detection circuit comprises a comparator circuit having a first input configured to receive the difference signal and a second input configured to receive a null reference signal.

23. The control circuit of claim 17, wherein a change in sign of said difference signal indicates occurrence of a zero-crossing event.

24. The control circuit of claim 23, wherein the drive control circuit comprises a logic circuit configured to process the zero-crossing event and determine a position of the rotor.

25. A control circuit for controlling operation of a brushless DC (BLDC) sensorless motor having a first terminal connected to a first winding, a second terminal connected to a second winding and a third terminal connected to a third winding, comprising:

a drive control circuit configured to control the generation of drive signals to the first and second terminals and place the third terminal in a high-impedance state;

wherein the drive signals include first drive signals at a first current magnitude and second drive signals at a second current magnitude different from the first current magnitude; and

a differencing circuit comprising;

a multiplexing circuit having a first input coupled to said third terminal and a second input coupled to a reference signal;

an analog to digital converter circuit having an input coupled to an output of the multiplexing circuit, said analog to digital converter circuit configured to convert the voltages at the third terminal and the reference signal to digital values; and

wherein the drive control circuit comprises a logic circuit configured to process the digital values to produce a difference signal.

26. The control circuit of claim 25, wherein the motor further comprises a center tap for windings of the motor, said reference signal comprising a voltage at the center tap.

27. The control circuit of claim 25, further comprising a virtual center tap circuit configured to provide a virtual center tap of the motor, said reference signal comprising a voltage at the virtual center tap.

28. The control circuit of claim 25, further comprising a zero-crossing detection circuit configured to receive the difference signal and detect a zero-crossing condition of the difference signal.

29. The control circuit of claim 28, wherein the drive control circuit comprises a logic circuit configured to process the detected zero-crossing condition and determine a position of the rotor.

30. The control circuit of claim 28, wherein the zero-crossing detection circuit comprises a comparator circuit having a first input configured to receive the difference signal and a second input configured to receive a null reference signal.

31. The control circuit of claim 25, wherein a change in sign of said difference signal indicates occurrence of a zero-crossing event.

32. The control circuit of claim 31, wherein the drive control circuit comprises a logic circuit configured to process the zero-crossing event and determine a position of the rotor.