Methods and systems for diagnosing faults for rotors of electric motors

1. A method for fault diagnosis for a rotor of an electric motor, the electric motor also having an inverter, the method comprising the steps of:

obtaining a current for the inverter;

determining a preliminary angle using a resolver angle of the rotor;

conducting a transformation of the current using a transformation angle, the transformation angle being equal to a product of the preliminary angle and a multiplier; and

identifying, via a processor, a fault condition using the transformation.

2. The method of claim 1 , wherein the preliminary angle comprises the resolver angle.

3. The method of claim 1 , wherein the preliminary angle comprises a slip angle of the rotor, and the step of determining the preliminary angle comprises the steps of:

calculating a flux angle of the rotor;

calculating the resolver angle of the rotor; and

subtracting the resolver angle from the flux angle, to thereby calculate the slip angle.

4. The method of claim 1 , further comprising the step of:

conducting a second transformation of the current using a second transformation angle, the second transformation angle being equal to a product of the preliminary angle and a second multiplier;

wherein the step of identifying the fault condition comprises the step of identifying, via the processor, the fault condition using the transformation and the second transformation.

5. The method of claim 4 , wherein:

the step of conducting the transformation comprises the step of conducting the transformation using a fault reference frame; and

the step of conducting the second transformation comprises the step of conducting the second transformation using the fault reference frame.

6. The method of claim 4 , wherein:

the second multiplier has a positive value; and

the multiplier has a negative value with an absolute value that is equal to the positive value.

7. The method of claim 4 , wherein the step of identifying the fault condition comprises the steps of:

processing results of the transformation through a digital filter, generating a first fault component;

processing results of the second transformation through the digital filter, generating a second fault component;

generating a fault index using the first fault component and the second fault component; and

identifying the fault condition using the fault index.

8. A method for fault diagnosis for a rotor of an electric motor, the electric motor also having an inverter, the method comprising the steps of:

obtaining a current for the inverter;

determining a preliminary angle using a resolver angle of the rotor;

multiplying the preliminary angle by a first multiplier to generate a first transformation angle;

multiplying the preliminary angle by a second multiplier to generate a second transformation angle;

conducting a first transformation of the current using the first transformation angle;

conducting a second transformation of the current using the second transformation angle; and

identifying, via a processor, a fault condition using the first transformation and the second transformation.

9. The method of claim 8 , wherein:

the step of conducting the first transformation comprises the step of conducting the first transformation using a fault reference frame; and

the step of conducting the second transformation comprises the step of conducting the second transformation using a fault reference frame.

10. The method of claim 8 , wherein:

the second multiplier has a positive value; and

the first multiplier has a negative value with an absolute value that is equal to the positive value.

11. The method of claim 8 , wherein the step of identifying the fault condition comprises the steps of:

processing results of the first transformation through a digital filter, generating a first fault component;

processing results of the second transformation through the digital filter, generating a second fault component;

generating a fault index using the first fault component and the second fault component; and

identifying the fault condition using the fault index.

12. The method of claim 8 , wherein the preliminary angle comprises the resolver angle.

13. The method of claim 12 , wherein:

the first multiplier is equal to negative one; and

the second multiplier is equal to one.

14. The method of claim 8 , wherein the preliminary angle comprises a slip angle of the rotor, and the step of determining the preliminary angle comprises the steps of:

calculating a flux angle of the rotor;

calculating the resolver angle of the rotor; and

subtracting the resolver angle from the flux angle, to thereby calculate the slip angle.

15. The method of claim 14 , wherein:

the first multiplier is equal to negative two; and

the second multiplier is equal to two.

16. A system for use with an electrical system comprising an electric motor having a rotor and a stator, and an inverter module coupled between an energy source and the stator, the inverter module being configured to provide a commanded voltage from the energy source to the stator, the system comprising:

a current sensor coupled between the energy source and the inverter module, the current sensor being configured to measure an input current for the inverter module; and

a control module coupled to the inverter module and the current sensor, the control module being configured to:

determine a preliminary angle using a resolver angle of the rotor;

conduct a first transformation of the input current using a first transformation angle that is equal to a first multiplier multiplied by the preliminary angle;

conduct a second transformation of the input current using a second transformation angle that is equal to a second multiplier multiplied by the preliminary angle; and

identify a fault condition using the first transformation and the second transformation.

17. The system of claim 16 , wherein the preliminary angle comprises the resolver angle.

18. The system of claim 17 , wherein:

the first multiplier is equal to negative one; and

the second multiplier is equal to one.

19. The system of claim 16 , wherein the preliminary angle comprises a slip angle of the rotor.

20. The system of claim 19 , wherein:

the first multiplier is equal to negative two; and

the second multiplier is equal to two.