Method and system for determining a position of a rotor of an electric motor with noise reduction

• US 8,796,983 B2
• Filed: 06/27/2011
• Issued: 08/05/2014
• Est. Priority Date: 02/24/2011
• Status: Active Grant

• Current Assignee: Deere & Company
• Original Assignee: Deere & Company
• Inventors: Wu, Long, Shaw, Robert
• Primary Examiner(s): Masih, Karen
• Application Number:
  US13/169,495
• Publication Number:
  US 20120217913A1
• Time in Patent Office: 1,135 Days
• Field of Search: 318/721, 318/400.04, 318/400.29, 318/701, 318/400.13, 318/599, 318/720
• US Class Current: 318/721
• CPC Class Codes: H02P 21/16 Estimation of constants, e.g. the rotor time constant
• CPC Class Codes: H02P 6/20 Arrangements for starting H02P6/08 takes precedence

Abstract

A data storage device stores previous position readings of the rotor for a previous cycle of a pulse width modulation signal applied to the motor. A current raw position reading for the current cycle is received. A predicted position reading for a current cycle is determined based on at least one of the stored previous position readings of the previous cycle. A data processor determines whether a difference between the current raw position reading and the predicted position reading for a first mode and a second mode is within one or more preset thresholds. The data processor selects the current raw position reading as a verified reliable final position reading if a first difference for the first mode is equal to or less than a primary preset threshold or if a second difference for the second mode is equal to or less than a secondary preset threshold.

Claims

1. A method of determining a position of a rotor in a motor, the method comprising:

storing a plurality of previous position readings of the rotor for a previous cycle of a pulse width modulation signal applied to the motor, the previous position readings comprising a previous cycle final selected position and a previous cycle raw position;

receiving a current raw position reading for the current cycle;

determining a predicted position reading for a current cycle based on at least one of the plurality of stored previous position readings of the previous cycle, the predicted position reading comprising the previous cycle final selected position for a first mode and the previous cycle raw position for a second mode;

determining whether a first difference between the current raw position reading and the predicted position reading for the first mode is within a primary preset threshold;

determining whether a second difference between the current raw position reading and the predicted position reading for the second mode is within a secondary preset threshold; and

selecting the current raw position reading as a verified reliable final position reading of the current cycle if the first difference for the first mode is equal to or less than the primary preset threshold or if the second difference for the second mode is equal to or less than the secondary preset threshold.

2. The method according to claim 1 further comprising:

selecting the predicted position for the first mode as a final selected position reading of current cycle if the first difference for the first mode is larger than the primary preset threshold and the second difference for the second mode is larger than the secondary preset threshold.

3. The method according to claim 1 further comprising:

selecting the verified reliable final position reading of current cycle by evaluation of a first difference between the current raw position reading and the current predicted position based on previous cycle final selected position and a second difference between the current raw position reading and the current predicted position based on previous cycle raw position.

4. The method according to claim 3 wherein the selecting further comprises selecting the current raw position as the verified reliable final position reading of current cycle if at least one of the first difference and the second difference is less than or equal to their respective primary and secondary preset thresholds.

5. The method according to claim 3 wherein the selecting further comprises selecting the predicted position based on previous cycle final selected position as the verified reliable final position reading of current cycle if both of the first difference and the second difference are greater than their respective primary and secondary preset thresholds.

6. The method according to claim 1 further comprising:

detecting whether the predicted position is consecutively used as the verified reliable final position for more than a maximum count number, and

switch off or reset the controller if the predicted position is consecutively used as the verified reliable final position for more than the maximum count number, where the maximum count number is a positive integer greater than three.

7. The method according to claim 1 further comprising:

associating respective time-stamps with the previous cycle raw position reading and the current cycle raw position reading;

determining a time difference between the previous cycle raw position reading and the current cycle raw position reading based on the associated respective time-stamps; and

adjusting the time period used for predicted position calculation when varying pulse width modulation switching frequency is applied to the motor to control the motor.

8. The method according to claim 1 wherein determining of the predicted position reading for the current cycle is based on the stored previous position reading from the previous cycle and a previous speed reading from the previous cycle.

9. The method according to claim 1 wherein determining the predicted position reading for the first mode for the current cycle is determined by the following equation:

Pos_pred_2a=Pos_1a+Spd_read_1*P1,

where Pos_pred_2a is the predicted position reading for the current cycle based on previous cycle raw position, Pos_1a is the previous raw position reading for the previous cycle, Spd_read_1 is the previous speed reading from the previous cycle, and P1 is the time difference between raw position reading times for the previous cycle and the current cycle.

10. The method according to claim 1 wherein determining the predicted position reading for the second mode for the current cycle is determined by the following equation:

Pos_pred_2b=Pos_—

1b+Spd_read_—

1*P1,

where Pos_pred_2b is the predicted position reading for the current cycle based on previous cycle final selected position, Pos_1b is the final selected position reading for the previous cycle, Spd_read_1 is the previous speed reading from the previous cycle, and P1 is the time difference between raw position reading times for the previous cycle and the current cycle.

11. A method of determining a position of a rotor in a motor with reduced noise, the method comprising:

storing a plurality of previous position readings of the rotor for a previous cycle of a pulse width modulation signal applied to the motor, the previous position readings comprising a previous cycle final selected position and previous cycle raw position;

receiving a current raw position reading for the current cycle of the pulse width modulation signal;

determining a predicted position reading for a current cycle based on the stored previous position readings of the previous cycle in accordance with a first mode or a second mode, where the first mode uses the previous cycle final selected position and where the second mode uses the previous cycle raw position;

determining whether a difference between at least one of the predicted positions based on previous position readings and the current raw position reading is within a preset threshold; and

selecting the current raw position reading as a verified reliable final position reading of current cycle if the difference is equal to or less than the preset threshold.

12. The method according to claim 11 wherein the determining whether the difference further comprises the following:

in the first mode, determining if a first difference between the current raw position reading and the predicted position based on previous final selected position is greater than a primary preset threshold as the preset threshold;

in the second mode, determining if a second difference between the current raw position reading and the predicted position based on previous raw position reading is greater than a secondary preset threshold as the preset threshold.

13. The method according to claim 12 wherein the selecting further comprises:

selecting the current raw position reading as a verified reliable final position reading of current cycle if the first difference is equal to or less than the primary preset threshold or if the second difference is equal to or less than the secondary preset threshold.

14. The method according to claim 12 wherein the selecting further comprises:

selecting the predicted position for the first mode or second mode as a verified reliable final position reading of current cycle if the first difference and the second difference each are larger than the preset threshold.

15. The method according to claim 12 further comprising:

selecting the predicted position based on previous final selected position reading as the verified reliable final position reading of current cycle if the first difference and the second difference are each greater than the preset threshold.

16. The method according to claim 12 wherein the selecting further comprises:

selecting the current raw position as the verified reliable final position reading of current cycle if the first difference is less than or equal to the primary threshold or if the second difference is less than or equal to than the primary preset threshold.

17. The method according to claim 12 wherein the selecting further comprises:

selecting the predicted position based on previous cycle raw position as the verified reliable final position reading of current cycle if each of the first difference and second difference is less than or equal to the preset threshold.

18. A system of determining a position of a rotor in a motor, the system comprising:

a data storage device for storing a plurality of previous position readings of the rotor for a previous cycle of a pulse width modulation signal applied to the motor, the previous position readings comprising a previous cycle final selected position and a previous cycle raw position;

a data port for receiving a current raw position reading for the current cycle from a sensor;

a data processor for executing software instructions within a primary processing module for determining a predicted position reading for a current cycle based on at least one of the plurality of stored previous position readings of the previous cycle, the predicted position reading comprising the previous cycle final selected position for a first mode and the previous cycle raw position for a second mode, the primary processing module comprising the software instructions stored in the data storage device on a non-transitory basis and adapted to cause the data processor to determine whether a difference between the current raw position reading and the predicted position reading for the first mode and the second mode is within a preset threshold, the primary processing module adapted to select the current raw position reading as a verified reliable final position reading if the difference is equal to or less than the preset threshold.

19. The system according to claim 18 wherein the primary data processing module is adapted to select the verified reliable final position reading by evaluation of a first difference between the current raw position reading and the predicted position based on previous cycle final selected position and a second difference between the predicted position based on current raw position reading and the previous cycle raw position.

20. The system according to claim 18 wherein the primary data processing module is adapted to select the current raw position as the verified reliable final position reading if at least one of the first difference or the second difference is less than or equal to than the preset threshold.

21. The system according to claim 18 wherein the primary data processing module is adapted to select the predicted position based on previous cycle final selected position as the verified reliable final position reading of current cycle if each of the first difference and the second difference is greater than the preset threshold.

22. The system according to claim 18 wherein the primary data processing module is adapted to select the predicted position based on previous cycle raw position as the verified reliable final position reading of current cycle if each of the first difference and the second difference is less than or equal to the preset threshold.