Self-tuning Pid Controller Based on Control Performance Evaluations

In steady state of process systems, reductions in cost and advances in quality are continuously pursued. Some process systems are considered time-variant systems with system characteristics that change according to the conditions and environments of the system operations. Previously, one of the authors proposed a design scheme of a selftuning PID control system, in which a user-specified parameter is tuned to maintain two control performances (variance of the control error and variance of the control input difference) based on the modeling performance assessment. As a result, efficient control is expected in the steady state. However, the transient state requires readiness and stability of the control systems. In this paper, the self-tuning control scheme is improved by adding a function to maintain two other control performances (overshoot and rise time) in the transient state. The tuning scheme of PID parameters is switched based on the steady state or the transient state. Finally, the effectiveness of the proposed control scheme is evaluated by simulation examples.