Diagnostic system and method for an electric motor using torque estimates

• US 7,116,068 B2
• Filed: 12/23/2003
• Issued: 10/03/2006
• Est. Priority Date: 04/12/2002
• Status: Expired due to Fees

• 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
• Primary Examiner(s): Donovan, Lincoln
• Assistant Examiner(s): GLASS, ERICK DAVID
• Application Number:
  US10/745,276
• Publication Number:
  US 20040134267A1
• Time in Patent Office: 1,015 Days
• Field of Search: None
• US Class Current: 318/400.15
• 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 with n phases, the system comprising:

a first subsystem to determine first currents of each motor phase;

a second subsystem to determine a first value of motor shaft position;

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

a fourth subsystem to determine second currents of each motor phase;

a fifth subsystem to determine a second value of motor shaft position;

a sixth subsystem to estimate a second value of motor torque, independent of the first estimate of motor torque, using the second currents and the second value 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 whereby a discrepancy between the first and second motor torque estimates is indicated.

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

a first current sensor of a first set of n−

1 current sensors for determining a first measured current of a first of phases of the electric motor;

a second current sensor of the first set of n−

1 current sensors for determining a first measured current of a second of n−

1 phases of the electric motor;

other current sensors of the first set of n−

1 current sensors for determining a first measured current of each of the other n−

1 phases of the electric motor; and

a system to estimate a first current of an n^th phase of the electric motor, including second and third phases, based on the first measured currents for the n−

1 current sensors.

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

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

a first current sensor of a second set of n−

1 current sensors for determining a second measured current of a first of n−

1 phases of the electric motor;

a second current sensor of the second set of n−

1 current sensors for determining a second measured current of a second set of n−

1 phases of the electric motor;

other current sensors of the second set of n−

1 current sensors for determining a second measured current of each of the other n−

1 phases of the electric motor; and

a system to estimate a second current of an n^th phase of the electric motor, including second and third phases, based on the second measured currents for the second set of n−

1 current sensors.

6. The diagnostic system of claim 1 wherein the fifth subsystem includes a resolver.

7. 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, greater than one, of the electric motor.

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

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

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

determining a first value of motor shaft position;

estimating a first value of motor torque using the first value of motor shaft position and the first set of currents;

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

1 current sensors;

determining a second value of motor shaft position;

estimating a second value of motor torque, independent of the first estimate of motor torque, using the second value of motor shaft position and the second set of currents; and

comparing the first and second estimates of motor torque.

9. The method according to claim 8 further comprising the step of notifying a motor operator of a potential discrepancy in electrical operating conditions.

10. The method according to claim 8 wherein the step of determining a first set of currents for each motor phase comprises:

determining a first set of currents of n−

1 phases of the electric motor with a set of n−

1 current sensors;

determining a second set of currents of n−

1 phases of the electric motor with a set of n−

1 current sensors; and

estimating two independent currents of an n^th phase of the electric motor, including second and third phases, based on the first and second sets of currents of the n−

1 phases of the electric motor.

11. The method according to claim 8 wherein the step of determining the first estimate of motor shaft position is accomplished by using a Kalman filter.

12. The method according to claim 8, wherein the step of determining a second value of motor shaft position is accomplished by using a resolver.

13. The method set forth in claim 8 wherein each step of generating independent estimates of motor torque comprises the use of n−

1 current sensors for each torque estimate.

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

a sub-system (172, 152, 154, 156, 158) to determine current in each motor phase;

a sub-system (182, 190) to determine first values of motor shaft position;

a sub-system (67, 176, 178) for generating a first estimate of motor torque using the current in each motor phase and the first value of motor shaft position;

a sub-system (182, 190) to determine a second value of motor shaft position;

a sub-system (67, 190, 114) for generating a second estimate of motor torque using current in each motor phase and a second value of motor shaft position; and

a sub-system (67) 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.