Digital PID type-III control loop design via the symmetrical optimum criterion

An analytical digital PID control law for the design of type-III control loops is developed. The proposed control law involves both dominant time constants of the controlled process, its unmodelled dynamics plus the sampling time of the controller. Basis of the proposed theory is the well known Symmetrical Optimum criterion. The development of the control law takes place in the frequency domain. For applying the proposed theory an accurate estimation of the plant's dominant time constants is required. The final control loop has the advantage of achieving zero steady state position, velocity and acceleration error. The potential of the proposed theory is justified via simulation examples for benchmark process models met frequently in many industry applications.