Methods and apparatus for fault-tolerant control of electric machines

• US 20040239272A1
• Filed: 06/02/2003
• Published: 12/02/2004
• Est. Priority Date: 06/02/2003
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: GM Global Technology Operations Incorporated (Motors Liquidation Co. GUC Trust)
• Inventors: Sul, Seung-Ki, Schulz, Steven E., Nagashima, James M., Patel, Nitinkumar R., Jeong, Yu-Seok
• Granted Patent: US 6,989,641 B2
• Time in Patent Office: Days
• US Class Current: 318/439
• CPC Class Codes: G05B 19/4062 Monitoring servoloop, e.g. overload of servomotor, loss of feedback or reference
• CPC Class Codes: G05B 2219/42329 Defective measurement, sensor failure
• CPC Class Codes: H02P 29/032 Preventing damage to the motor, e.g. setting individual current limits for different drive conditions

Abstract

A method for controlling an electric machine having current sensors for less than every phase of the electric machine includes operating a processor to perform a test to preliminarily determine whether a fault exists in one or more of the current sensors and a test to finally determine that the fault exists in the one or more current sensors. The method further includes operating the processor to utilize a state observer of the electric machine to estimate states of the electric machine, wherein the state observer is provided state input measurements from each non-faulty current sensor, if any. Measurements from the current sensor or sensors determined to be faulty are disregarded. The processor controls the electric machine utilizing results from the state observer.

Claims

1. A method for controlling an electric machine having current sensors for less than every phase of the electric machine, when a fault occurs in one or more of the current sensors, said method comprising operating a processor to:

perform a test to determine whether a fault exists in one or more of the current sensors;

utilize a state observer of the electric machine to estimate states of the electric machine, wherein said state observer is provided input measurements from non-faulty current sensors, if any, disregarding measurements from the current sensor or sensors determined to be faulty; and

control the electric machine utilizing results from the state observer.

2. A method in accordance with claim 1 wherein said performing a test to determine that a fault exists in one or more of the current sensors comprises operating a processor to:

perform a test to preliminarily determine that a fault exists in one or more current sensors; and

perform a test to finally determine that the fault exists in the one or more current sensors.

3. A method in accordance with claim 2 wherein the electric machine is a three-phase motor having three windings with current sensors on two of the three windings, and wherein performing a test to preliminarily determine that a fault exists in one or more current sensors comprises operating a processor to:

apply a first test voltage waveform to the two of the three windings having a current sensor;

sample measurements from the two current sensors as a function of time;

perform a balancing test on the two windings with current sensors utilizing the sampled measurements;

perform a gain error test on the current sensors utilizing the sampled measurements;

perform an offset error test on the two current sensors utilizing the sampled measurements, and

determine, utilizing said tests, that a fault exists and preliminarily identify which of the two current sensors may be at fault.

4. A method in accordance with claim 3 wherein said performing a balancing test comprises operating the processor to determine whether the sampled currents in each of the two of the three windings represented by the sampled measurements are of equal magnitude and opposite phase, within a predetermined limit.

5. A method in accordance with claim 3 wherein said performing a gain error test comprises operating the processor to determine whether the root mean square values of the sampled currents in each of the two of the three windings represented by the sampled measurements are within a predetermined nominal range.

6. A method in accordance with claim 3 wherein said performing an offset error test comprises operating the processor to determine whether the sum of the sampled currents in the two windings represented by the sampled measurements are less than a predetermined value or values.

7. A method in accordance with claim 3 further comprising, when a fault exists, operating a processor to:

successively apply a second test voltage waveform between each pair of the three windings with the remaining non-paired winding shorted to one winding of the pair;

sample measurements from the two current sensors as a function of time;

determine, utilizing said sampled measurements resulting from the application of the second test voltage, that the identified current sensor is at fault.

8. A method in accordance with claim 1 wherein said operating the processor to utilize a state observer of the electric machine to estimate states of the electric machine comprises regulating current in a rotating d-q axis in accordance with an estimated d-q current observed by a closed loop observer.

9. A method in accordance with claim 1 wherein said operating the processor to utilize a state observer of the electric machine to estimate states of the electric machine comprises regulating current in a rotating d-q axis in accordance with an estimated d-q current observed by an open loop observer.

10. A method in accordance with claim 1 wherein said state observer is a synchronous frame current estimator.

11. An apparatus for controlling an electric machine having current sensors for less than every one of its phases, said apparatus comprising:

an inverter configured to provide current to the electric machine;

a processor configured to control the current provided to the electric machine by the inverter in accordance with a desired torque, power, or speed;

said processor further configured to utilize the inverter to test the current sensors to determine whether a fault exists in one or more of the current sensors, and if a fault is determined to exist, to utilize a state observer of the electric machine to estimate states of the electric machine, utilizing state input measurements from each non-faulty current sensor, if any, disregarding the current sensor or sensors determined to be faulty; and

to control the electric machine utilizing the inverter and results from the state observer.

12. An apparatus in accordance with claim 11 wherein said processor is further configured to:

perform a test to preliminarily determine that a fault exists in one or more of the current sensors; and

perform a test to finally determine that the fault exists in the one or more current sensors.

13. An apparatus in accordance with claim 12 wherein the electric machine is a three-phase motor having three windings with current sensors on two of the three windings, and wherein to perform a test to preliminarily determine that a fault exists in one or more of the current sensors, said processor is configured to:

operate the inverter to apply a first test voltage waveform to the two of the three windings having a current sensor;

sample measurements from the two current sensors as a function of time;

perform a balancing test on the two windings with current sensors utilizing the sampled measurements;

perform a gain error test on the current sensors utilizing the sampled measurements;

perform an offset error test on the two current sensors utilizing the sampled measurements; and

determine, utilizing said tests, that a fault exists and preliminarily identify which of the two current sensors may be at fault.

14. An apparatus in accordance with claim 13 wherein to perform a balancing test, said processor is further configured to determine whether the sampled currents in each of the two of the three windings represented by the sampled measurements are of equal magnitude and opposite phase, within a predetermined limit.

15. An apparatus in accordance with claim 13 wherein to perform a gain error test, said processor is further configured to determine whether the root mean square values of the sampled currents in each of the two of the three windings represented by the sampled measurements are within a predetermined nominal range.

16. An apparatus in accordance with claim 13 wherein to perform an offset error test, said processor is configured to determine whether the sums of the sampled currents in the two windings represented by the sampled measurements are less than a predetermined value or values.

17. An apparatus in accordance with claim 13 wherein said processor is configured to:

control the inverter to successively apply a second test voltage waveform between each pair of the three windings with the remaining non-paired winding shorted to one winding of the pair;

sample measurements from the two current sensors as a function of time; and

determine, utilizing the sampled measurements resulting from the application of the second test voltage, that the identified current sensor is at fault.

18. An apparatus in accordance with claim 11 wherein to control the electric machine utilizing the inverter and the state observer, said processor is configured to operate the inverter to regulate current in a rotating d-q axis in accordance with an estimated d-q current observed by a closed loop observer.

19. An apparatus in accordance with claim 11 wherein to control the electric machine utilizing the inverter and the state observer, said processor is configured to regulate current in a rotating d-q axis in accordance with an estimated d-q current observed by an open loop observer.

20. An apparatus in accordance with claim 11 wherein the state observer is a synchronous frame current estimator and the electric machine is an interior permanent magnet motor.