Method and system for detecting a failed current sensor in a three-phase machine

• US 20100033122A1
• Filed: 08/06/2008
• Published: 02/11/2010
• Est. Priority Date: 08/06/2008
• Status: Active Grant

• Current Assignee: Caterpillar Incorporated, Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Caterpillar Incorporated
• Inventors: Gerdes, Jesse R., Wai, Jackson, Speckhart, Gregory J., Hartman, Mark E.
• Granted Patent: US 8,004,226 B2
• Time in Patent Office: Days
• US Class Current: 318/490
• CPC Class Codes: H02P 29/0241 the fault being an overvoltage

Abstract

A method of detecting one or more failed current sensor and estimating a phase current for the failed current sensor on a three-phase machine is disclosed. The method may include detecting one or more failed current sensor by determining if an absolute value of a sum of the phase currents of the motor is below an open circuit value. The method may also include determining which phase currents are approximately zero, for each phase current associated with each phase of the motor, if the sum of the phase currents of the motor is not below the open circuit value. The method may further include estimating the phase current for the failed current sensor by determining the phase current value for the failed current sensor, that when added to the phase currents of the remaining current sensors, will make the sum of all the phase currents equal to approximately zero.

Claims

1. A method of detecting one or more failed current sensor and estimating a phase current for the failed current sensor on a three-phase machine, comprising:

detecting one or more failed current sensor, including;

determining if an absolute value of a sum of the phase currents of the motor is below an open circuit value;

determining which phase currents are approximately zero, for each phase current associated with each phase of the motor, if the sum of the phase currents of the motor is not below the open circuit value;

estimating the phase current for the failed current sensor by determining the phase current value for the failed current sensor, that when added to the phase currents of the remaining current sensors, will make the sum of all the phase currents equal to approximately zero.

2. The method of claim 1, wherein the open circuit value is equal to zero.

3. The method of claim 1, wherein determining which phase currents are approximately zero includes waiting a first delay period after determining if the absolute value of the sum of the phase currents of the motor is below the open circuit value.

4. The method of claim 3, further including waiting a second delay period, if less than one or two or more phase currents are approximately zero, then again determining which phase currents are approximately zero.

5. The method of claim 4, further including:

estimating the phase current for the failed current sensor if only one phase current is approximately zero;

determining a non-open circuit current sensor failure if no phase currents are approximately zero a predetermined number of times in a row; and

determining that two or more current sensors have failed if more than one phase current is approximately zero the predetermined number of times in a row.

6. The method of claim 1, further including requalifying the failed current sensor, including:

determining if the absolute value of the sum of the phase currents of the motor is below the open circuit value, when using the actual current sensor values; and

determining if the actual phase current of the failed current sensor is greater than approximately zero.

7. The method of claim 6, further including:

incrementing a counter if both the absolute value of the sum of the actual phase currents of the motor is below the open circuit value, and the actual phase current of the failed current sensor is greater than approximately zero;

otherwise decrementing the counter; and

requalifying the failed current sensor when the counter is above a selected integer.

8. The method of claim 1, further including detecting the failed current sensor and estimating the phase current for the failed current sensor at every current sensor sample.

9. A system for detecting one or more failed current sensor and estimating a phase current for the failed current sensor on a three-phase machine, comprising:

at least one three-phase machine;

at least one sensor deployed per phase of each three-phase machine; and

a controller electrically coupled to the at least one three-phase machine, the controller configured to;

detect one or more failed current sensor, including;

determine if an absolute value of a sum of the phase currents of the three-phase machine is below an open circuit value;

determine which phase currents are approximately zero, for each phase current associated with each phase of the motor, if the absolute value of the sum of the phase currents of the three-phase machine is not below the open circuit value;

estimate the phase current for the failed current sensor by determining the phase current value for the failed current sensor, that when added to the phase currents of the remaining current sensors, will make the sum of all the phase currents equal to approximately zero.

10. The system of claim 9, wherein the open circuit value is equal to zero.

11. The system of claim 9, wherein determining which phase currents are approximately zero includes the controller waiting a first delay period after determining if the absolute value of the sum of the phase currents of the motor is below the open circuit value.

12. The system of claim 11, wherein the controller is further configured to wait a second delay period, if less than one or two or more phase currents are approximately zero, and then again determine which phase currents are approximately zero.

13. The system of claim 12, wherein the controller is further configured to:

estimate the phase current for the failed current sensor if only one phase current is approximately zero;

determine a non-open circuit current sensor failure if no phase currents are approximately zero a predetermined number of times in a row; and

determine that two or more current sensors have failed if more than one phase current is approximately zero the predetermined number of times in a row.

14. The system of claim 9, wherein the controller is configured to requalify the failed current sensor, wherein requalifying the failed current sensor includes:

determining if the absolute value of the sum of the phase currents of the motor is below the open circuit value, when using the actual current sensor values; and

determining if the actual phase current of the failed current sensor is greater than approximately zero.

15. The system of claim 14, wherein the controller is further configured to:

increment a counter if both the absolute value of the sum of the actual phase currents of the motor is below the open circuit value, and the actual phase current of the failed current sensor is greater than approximately zero;

otherwise decrement the counter; and

requalify the failed current sensor when the counter is above a selected integer.

16. The system of claim 9, wherein the controller is further configured to detect the failed current sensor and estimate the phase current for the failed current sensor at every current sensor sample.

17. A machine, comprising:

a power source;

at least one motor, each motor having at least two phases and a current sensor associated with each phase of the motor; and

a controller electrically coupled to the at least one motor, and the controller configured to;

detect one or more failed current sensor, including;

determine if an absolute value of a sum of the phase currents of the motor is below an open circuit value;

determine which phase currents are approximately zero, for each phase current associated with each phase of the motor, if the absolute value of the sum of the phase currents of the motor is not below the open circuit value;

estimate the phase current for the failed current sensor by determining the phase current value for the failed current sensor, that when added to the actual phase currents of the remaining current sensors, will make the sum of all the phase currents equal to approximately zero.

18. The machine of claim 17, wherein determining which phase currents are approximately zero further includes:

waiting a first delay period after determining if the absolute value of the sum of the phase currents of the motor is below the open circuit value;

waiting a second delay period if less than one or two or more phase currents are approximately zero, then again determine which phase currents are approximately zero;

estimating the phase current for the failed current sensor if only one phase current is approximately zero;

determining a non-open circuit current sensor failure if no phase currents are approximately zero a predetermined number of times in a row; and

determining that two or more current sensors have failed if more than one phase current is approximately zero the predetermined number of times in a row.

19. The machine of claim 17, wherein the controller is configured to requalify the failed current sensor, wherein requalifying the failed current sensor includes:

determining if the absolute value of the sum of the phase currents of the motor is below the open circuit value, when using the actual current sensor values;

determining if the actual phase current of the failed current sensor is greater than approximately zero;

incrementing a counter if both the absolute value of the sum of the actual phase currents of the motor is below the open circuit value, and the actual phase current of the failed current sensor is greater than approximately zero;

otherwise decrementing the counter; and

requalify the failed current sensor when the counter is above a selected integer.

20. The machine of claim 17, wherein the controller is further configured to detect the failed current sensor and estimate the phase current for the failed current sensor at every current sensor sample.