A simple approach for on-line PI controller tuning using closed-loop setpoint responses

摘要

A simple and new procedure has been developed for the PI controller tuningrnof an unidentified process using closed-loop responses. The method requires only onernstep test in the closed-loop system to obtain the proportional gain and integral time. Thernstep test is a setpoint change performed with a proportional only controller whilerndisabling any integral and derivative action. From the setpoint response one observesrnthe overshoot and the corresponding time to reach the peak. In addition one observes thernproportional gain (k_(c0)) and the steady-state offset. Based on a range of first-order withrndelay test processes, a simple analytical correlation has been developed for therncontroller gain (k_c/k_(c0)) as a function of the overshoot. The integral time setting is mainlyrna function of the time to reach the peak. The settings were derived to match the SIMCrntuning rule (with τ_c=θ) which gives good robustness with a gain margin of about 3 andrnsensitivity peak (M_s-value) of about 1.6. The proposed tuning method, originallyrnderived for first-order with delay processes, has been tested on a broad range of otherrnstable and integrating processes. The results using the closed-loop data are comparablernwith the SIMC tuning rule using the open-loop model.