Instability detection and adaptive-adjustment for active noise cancellation system

1. An active noise cancellation (ANC) system comprising:

at least one loudspeaker to project anti-noise sound within a passenger cabin of a vehicle in response to receiving an anti-noise signal;

at least one microphone to provide an error signal indicative of noise and the anti-noise sound within the passenger cabin;

an adaptive filter controller programmed to:

filter the error signal to obtain a noise reduction ratio, and

adjust a step size parameter based on a comparison of the noise reduction ratio to a noise threshold; and

a controllable filter to generate the anti-noise signal based on the adjusted step size parameter, and

wherein the adaptive filter controller is further programmed to:

filter the error signal using a transfer function to obtain an estimated virtual microphone error signal; and

filter the estimated virtual microphone error signal to obtain the noise reduction ratio.

2. The ANC system of claim 1 , wherein the adaptive filter controller is further programmed to:

detect an occurrence of noise boosting based on the comparison of the noise reduction ratio to the noise threshold; and

decrease the step size parameter in response to detection of noise boosting.

3. The ANC system of claim 1 , wherein the adaptive filter controller is further programmed to decrease the step size parameter in response to the noise reduction ratio being less than or equal to the noise threshold.

4. The ANC system of claim 1 , wherein the adaptive filter controller is further programmed to increase the step size parameter in response to the noise reduction ratio being greater than the noise threshold, and an automatic tuning step size parameter being less than a minimum step size parameter.

5. The ANC system of claim 1 , wherein the adaptive filter controller is further programmed to maintain the step size parameter in response to the noise reduction ratio being greater than the noise threshold, and an automatic tuning step size parameter being greater than a minimum step size parameter.

6. The ANC system of claim 1 , wherein the adaptive filter controller is further programmed to adjust the step size parameter and a leakage parameter based on the comparison of the noise reduction ratio to the noise threshold.

7. The ANC system of claim 6 , wherein the adaptive filter controller is further programmed to decrease the step size parameter and the leakage parameter in response to the noise reduction ratio being less than or equal to the noise threshold.

8. The ANC system of claim 6 , wherein the adaptive filter controller is further programmed to:

increase the step size parameter in response to the noise reduction ratio being greater than the noise threshold, and an automatic tuning step size parameter being less than a minimum step size parameter; and

increase the leakage parameter in response to the noise reduction ratio being greater than the noise threshold, and an automatic tuning leakage parameter being less than a minimum leakage parameter.

9. The ANC system of claim 6 , wherein the adaptive filter controller is further programmed to:

maintain the step size parameter in response to the noise reduction ratio being greater than the noise threshold, and an automatic tuning step size parameter being greater than a minimum step size parameter; and

maintain the leakage parameter in response to the noise reduction ratio being greater than the noise threshold, and an automatic tuning leakage parameter being greater than a minimum leakage parameter.

10. The ANC system of claim 6 , wherein the adaptive filter controller is further programmed to:

compare a frequency of the error signal to a frequency threshold value;

adjust the step size parameter in response to the frequency of the error signal being greater than the frequency threshold value; and

adjust the leakage parameter in response to the frequency of the error signal being less than the frequency threshold value.

11. An active noise cancellation (ANC) system comprising:

at least one loudspeaker to project anti-noise sound within a passenger cabin of a vehicle in response to receiving an anti-noise signal; and

a controller configured to:

filter an error signal indicative of noise and the anti-noise sound within the passenger cabin to obtain a noise reduction ratio,

adjust a step size parameter and a leakage parameter based on a comparison of the noise reduction ratio to a noise threshold,

generate the anti-noise signal based on the adjusted step size parameter and the adjusted leakage parameter,

detect an occurrence of noise boosting based on the comparison of the noise reduction ratio to the noise threshold, and

decrease at least one of the step size parameter and the leakage parameter in response to detection of noise boosting.

12. The ANC system of claim 11 , wherein the controller is further configured to detect the occurrence of noise boosting in response to the noise reduction ratio being less than or equal to the noise threshold.

13. The ANC system of claim 11 , wherein the controller is further configured to:

detect an occurrence of no noise boosting based on the comparison of the noise reduction ratio to the noise threshold;

increase the step size parameter in response to detection of no noise boosting and an automatic tuning step size parameter being less than a minimum step size parameter; and

increase the leakage parameter in response to detection of no noise boosting and an automatic tuning leakage parameter being less than a minimum leakage parameter.

14. The ANC system of claim 13 , wherein the controller is further configured to detect the occurrence of no noise boosting in response to the noise reduction ratio being greater than the noise threshold.

15. A method for controlling stability in an active noise cancellation (ANC) system, the method comprising:

receiving an error signal from a microphone indicative of noise and anti-noise sound within a passenger cabin;

filtering the error signal to obtain a noise reduction ratio;

detecting an occurrence of noise boosting based on a comparison of the noise reduction ratio to a noise threshold;

decreasing a step size parameter in response to detection of noise boosting;

generating an anti-noise signal, to be radiated from a loudspeaker within the passenger cabin as the anti-noise sound, based on the decreased step size parameter;

detecting an occurrence of no noise boosting based on the comparison of the noise reduction ratio to the noise threshold;

increasing the step size parameter in response to detection of no noise boosting; and

generating the anti-noise signal based on the increased step size parameter.

16. The method of claim 15 , further comprising detecting the occurrence of noise boosting in response to the noise reduction ratio being less than or equal to the noise threshold.

17. The method of claim 15 , further comprising detecting the occurrence of no noise boosting in response to the noise reduction ratio being greater than the noise threshold.