Practical aspects of PID auto-tuners based on relay feedback

Abstract

The performance of an automatic PID controller tuning method based on relay feedback is studied in the presence of deterministic disturbances. It is found that the occurence of any static load disturbance could cause significant errors in the estimates of the ultimate gain and period. However, the resultant asymmetry of the relay switching intervals can be used as an error indicator, or used to compute a self-corrective bias to restore accuracy of the estimates. This corrective bias is found to be functional even in the presence of moderate nonlinearity.