Method and systems for diagnosing an engine

1. A system, comprising:

a generator coupled to an engine and configured to generate electricity from rotational movement of a shaft of the engine;

one or more traction motors driven by the generator through a rectifier that produces a DC link voltage to one or more inverters;

a sensor configured to measure the DC link voltage; and

a controller configured to:

detect engine imbalance based on a frequency content of a signal output from the sensor in response to a contribution to the frequency content from the one or more inverters being less than a threshold value, including determining an inverter frequency of each inverter and, if the inverter frequency is within a threshold range of an engine rotational frequency, indicating the contribution is above the threshold value.

2. The system of claim 1 , wherein the controller is configured to, in response to the contribution being above the threshold value, delay the detection of the engine imbalance until the contribution is less than the threshold value.

3. The system of claim 1 , wherein to detect engine imbalance, the controller is configured to compare a magnitude of a selected frequency of the frequency content to a first threshold magnitude and indicate engine imbalance if the magnitude exceeds the first threshold magnitude.

4. The system of claim 3 , wherein the controller is configured to, in response to the contribution being above the threshold, adjust the detection of the engine imbalance by comparing the magnitude of the selected frequency to a second threshold magnitude, higher than the first threshold magnitude, and indicate imbalance when the magnitude exceeds the second threshold magnitude.

5. The system of claim 1 , wherein to determine if the contribution to the frequency content by the one or more inverters is greater than the threshold value, the controller is configured to:

identify one or more sidebands of a selected frequency of the frequency content; and

if a magnitude of a sum of the one or more sidebands exceeds a threshold magnitude, indicate the one or more inverters are contributing to the frequency content.

6. The system of claim 1 , wherein the controller is further configured to detect engine imbalance based on the frequency content of the signal output from the sensor in response to a contribution to the frequency content from a change in engine operation being less than the threshold value.

7. The system of claim 1 , wherein the controller is configured to, responsive to detecting engine imbalance, adjust one or more engine operating parameters.

8. A method for a vehicle system, comprising:

determining a frequency content of a signal output from a sensor configured to measure a parameter of a generator coupled to an engine of the vehicle system;

identifying whether a contribution to the determined frequency content by one or more vehicle system components at one or more selected frequencies is greater than a threshold;

when the contribution is not greater than the threshold, detecting engine imbalance based on the one or more selected frequencies of the determined frequency content, and adjusting an engine operating parameter in response to the detected engine imbalance; and

when the contribution is greater than the threshold, adjusting the detecting of the engine imbalance based on the one or more selected frequencies of the determined frequency content.

9. The method of claim 8 , wherein adjusting the detecting of the engine imbalance based on the determined frequency content comprises delaying the detecting of the engine imbalance until the contribution is not greater than the threshold, and wherein the one or more vehicle system components comprise one or more of an inverter, an alternator, or a generator auxiliary load.

10. The method of claim 8 , wherein detecting engine imbalance based on the determined frequency content comprises comparing a magnitude of the one or more selected frequencies of the frequency content to a first threshold magnitude and indicating engine imbalance if the magnitude exceeds the first threshold magnitude.

11. The method of claim 10 , wherein adjusting the detecting of the engine imbalance based on the determined frequency content comprises adjusting the first threshold magnitude to a second, higher threshold magnitude.

12. The method of claim 8 , wherein the one or more vehicle system components comprise an inverter, and wherein identifying whether the contribution to the determined frequency content by the one or more vehicle system components at the one or more selected frequencies is greater than the threshold includes identifying whether a frequency of the inverter is within a threshold range of an engine frequency.

13. A system, comprising:

an engine having a plurality of cylinders;

a generator coupled to the engine and configured to generate electricity from rotational movement of a shaft of the engine;

one or more traction motors driven by the generator through a rectifier that produces a DC link voltage to one or more inverters;

a sensor configured to measure the DC link voltage; and

a controller configured to:

identify one or more sidebands of a selected frequency of frequency content of a signal output by the sensor;

when a first magnitude of a sum of the one or more sidebands exceeds a first threshold magnitude, indicate the one or more inverters are contributing to the frequency content of the signal output by the sensor; and

when the first magnitude does not exceed the first threshold magnitude, indicate engine imbalance based on a second magnitude of the selected frequency exceeding a second threshold magnitude.

14. The system of claim 13 , wherein the controller is configured to, responsive to indicating the one or more inverters are contributing to the frequency content, delay the indication of engine imbalance until the first magnitude drops below the first threshold magnitude.

15. The system of claim 13 , wherein the controller is configured to, responsive to indicating engine imbalance, adjust one or more engine operating parameters.