Kapalı kontrol döngülerinde performans izleme

In this study, the performance of the control loops in different refinery units has been evaluated. The minimum variance controller, designated as benchmark and the proximity to expected performance of the current performance has been quantified using performance index. For accurate calculation of the performance index, optimum values of certain parameters have been determined. It has been shown that sampling interval is insufficient for some loops and the estimated value of dead time is different from the actual value. The classification has been made on the basis of calculated performance index and root causes affecting the performance have been estimated with different methods. Diagnosing the root-cause has been initiated by the spectral analysis expressed as a classical and visual approach and oscillation has been detected by looking the magnitude of the peaks at the power spectral analysis. The results obtained have been supported by the methods depending on the auto-covariance function and time-domain. Equipment faults, controller parameter values and external disturbances cause the oscillation. To understand where the oscillation originated from, nonlinearity and stiction analysis were performed respectively. The higher-order statictics were used in nonlinearity analysis and interactions between frequency pairs have been examined. Stiction analysis has been made to reveal potential equipment faults in the control loops containing non-linearity. According to the results, it was concluded that valve is problematic in the presence of stiction. In the case of appearance of oscillating behavior has been emphasized that poor performance is arised from parameter settings or external disturbances.