Synthesis of PID tuning for a new parallel cascade control structure

Most of the published papers on parallel cascade control strategies present improvement of dynamic performance of stable processes. In this paper, a new parallel cascade control scheme is proposed for controlling stable and unstable processes with time delay. The two main features of the proposed scheme are: the primary process output completely tracks the primary setpoint and the servo response decouples the regulatory response in the nominal system. The proposed structure has only two controllers. The inner loop controller is designed based on IMC approach. The outer loop controller is a PID controller in series with lead/lag filter which is designed based on the desired complementary sensitivity function. Significant improvement in the load disturbance rejection performances are obtained when compared to some recent methods in the literature. Simulation results show the superiority and usefulness of the proposed control method over the existing ones.