Diagnostic system and method for an electric motor using torque estimates

• US 20040134267A1
• Filed: 12/23/2003
• Published: 07/15/2004
• Est. Priority Date: 04/12/2002
• Status: Active Grant

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Boesch, Mathew, Raftari, Abbas, Garg, Vijay
• Granted Patent: US 7,116,068 B2
• Time in Patent Office: Days
• US Class Current: 73/118.1
• CPC Class Codes: B60K 1/02 comprising more than one electric motor
• CPC Class Codes: B60K 6/365 with the gears having orbital motion
• CPC Class Codes: B60K 6/445 Differential gearing distribution type
• CPC Class Codes: B60L 2240/423 Torque
• CPC Class Codes: B60W 10/06 including control of combustion engines
• CPC Class Codes: B60W 10/08 including control of electric propulsion units, e.g. motors or generators
• CPC Class Codes: B60W 20/00 Control systems specially adapted for hybrid vehicles hybrid vehicle design, B60K6/00; electric vehicles B60L
• CPC Class Codes: B60W 2710/0666 Engine torque
• CPC Class Codes: B60W 2710/083 Torque
• CPC Class Codes: B60W 50/04 Monitoring the functioning of the control system
• CPC Class Codes: H02K 21/00 Synchronous motors having permanent magnets; Synchronous generators having permanent magnets
• CPC Class Codes: H02P 23/14 Estimation or adaptation of motor parameters, e.g. rotor time constant, flux, speed, current or voltage
• CPC Class Codes: H02P 25/024 controlled by supply frequency
• CPC Class Codes: H02P 25/08 Reluctance motors
• CPC Class Codes: Y02T 10/62 Hybrid vehicles
• CPC Class Codes: Y02T 10/64 Electric machine technologies in electromobility

Abstract

A system and method for diagnosing a potential electrical operating discrepancy in a polyphase electric motor by generating two independent torque estimates using a plurality of current sensors and, optionally, a shaft position sensor. Differences between the independent torque estimates are used to indicate potential discrepancies in electrical operating characteristics of the motor.

Claims

1. A diagnostic system for a polyphase electric motor comprising:

a first subsystem to determine current of each motor phase;

a second subsystem to generate a first estimate of motor shaft position;

a third subsystem to generate a first estimate of motor torque using the first subsystem and the first estimate of motor shaft position;

a fourth subsystem to determine current of each motor phase;

a fifth subsystem to generate a second estimate of motor shaft position;

a sixth subsystem to generate a second estimate of motor torque, independent of the first estimate of motor torque, using the fourth subsystem and the second estimate of motor shaft position; and

a comparator system to compare the first and second estimates of motor torque.

2. The diagnostic system according to claim 1 further comprising an operator notification system.

3. The diagnostic system according to claim 1, wherein the first subsystem comprises:

a first current sensor generating a first measured current of a first phase of the electric motor;

a second current sensor generating a first measured current of a second phase of the electric motor; and

a system to generate a first estimated current of a third phase of the electric motor based on the first measured current of the first phase and the first measured current of the second phase.

4. The diagnostic system according to claim 1 wherein the second subsystem is a first Kalman filter.

5. The diagnostic system according to claim 1 wherein the fourth subsystem comprises:

a third current sensor generating a second measured current of a first phase of the electric motor;

a fourth current sensor generating a second measured current of a second phase of the electric motor; and

a second system to generate a second estimated current of a third phase of the electric motor based on the second measured current of the first phase and the second measured current of the second phase.

6. The diagnostic system according to claim 1 wherein the fourth subsystem comprises:

a third current sensor generating a second measured current of a first phase of the electric motor;

a fourth current sensor generating a first measured current of a third phase of the electric motor; and

a system to generate an estimated current of the second phase of the electric motor based on the second measured current of the first phase and the first measured current of the third phase.

7. The diagnostic system according to claim 4 wherein the sixth subsystem is a second Kalman filter.

8. The diagnostic system of claim 1 wherein the fifth subsystem is a resolver.

17. The diagnostic system set forth in claim 1 wherein the first and fourth subsystems include n−

1 current sensors for each of two motor torque estimates, where n=the number of phases in the electric motor.

9. A method to diagnose potential discrepancies in electrical operating characteristics in a polyphase electric motor comprising the steps of:

determining a first set of currents for each motor phase with n−

1 sensors, where n is any number of phases greater than one;

generating a first estimate of motor shaft position;

generating a first estimate of motor torque using the first estimate of motor shaft position;

determining a second set of currents for each motor phase using a number of current sensors from n to (2n−

2);

generating a second estimate of motor shaft position;

generating a second estimate of motor torque, independent of the first estimate of motor torque, using the second estimate of motor shaft position; and

comparing the first and second estimates of motor torque.

10. The method according to claim 9 further comprising the step of notifying a motor operator of a potential discrepancy in electrical operating conditions.

11. The method according to claim 9 wherein the step of determining a first set of currents for each motor phase comprises:

generating a first measured current of a first phase of the electric motor with a first current sensor;

generating a first measured current of a second phase of the electric motor with a second current sensor; and

generating a first estimated current of a third phase of the electric motor based on the first measured current of the first phase and the first measured current of the second phase.

12. The method according to claim 9 wherein the step of generating the first estimate of motor shaft position is accomplished by using a first Kalman filter.

13. The method according to claim 9 wherein the steps of determining sets of currents for each motor phase comprise:

generating a first set of measured currents of n−

1 phases of the electric motor with n−

1 current sensors;

generating a second set of measured currents for n-1 phases of the electric motor with another set of n−

1 current sensors; and

generating two independent estimated currents of an nth phase of the electric motor based on n−

1 measured currents from the first set and the second set of measured currents.

14. The method according to claim 12, wherein the step of generating the second estimate of motor shaft position is accomplished by using a second Kalman filter.

15. The method according to claim 9, wherein the step of generating a second estimate of motor shaft position is accomplished by using a resolver.

18. The method set forth in claim 9 wherein the step of determining current in each motor phase includes measuring current in each phase with n−

1 current sensors, where n =the number of phases in the electric motor;

each step of generating independent estimates of motor torque comprising the use of n−

1 current sensors for each torque estimate.

16. A controller in a system for diagnosing potential discrepancies in electrical operating conditions in a polyphase electric motor, the controller comprising:

a sub-system to determine current in each motor phase;

a sub-system for generating a first estimate of motor shaft position;

a sub-system for generating a first estimate of motor torque using the current in each motor phase and the first estimate of motor shaft position;

a sub-system for generating a second estimate of motor torque using current in each motor phase and a second estimate of motor shaft position; and

a sub-system for comparing the first and second estimates of motor torque for discrepancies whereby a motor operator can be notified of a potential discrepancy in electrical operating characteristics.