Analytical design of discrete PI–PR controllers via dominant pole assignment

In this study, a new discrete proportional integral–proportional retarded (D-PI–PR) controller design method is proposed. The proposed controller involves replacing the PD controller in the classical PI–PD control structure with a PR controller in discrete time and is implemented using dominant pole assignment, which is carried out by help of the modified Nyquist plot approach. The method starts with the determination of the controller parameters K_i and K_r in terms of the parameter K_p for a chosen delay parameter h after the computation of the desired dominant poles depending on the required closed-loop system performance criteria. The next step is to find the feasible K_p interval, in which the dominant pole assignment is guaranteed. To eliminate the unwanted impact of the controller zeros on the transient response of the system, the D-PIR structure is then transformed into the D-PI–PR structure. For the demonstration of the success of the proposed algorithm, first, second and third-order systems with time delays are used and the simulation results are compared with some other PID-type controllers design methods from the literature.