Cascade control based on minimum sensitivity in outer loop for processes with time delay

A new cascade control program was proposed based on modified internal model control to handle stable, unstable and integrating processes with time delay. The program had totally four controllers of which the secondary loop had two controllers and the primary loop had two controllers. The two secondary loop controllers were designed using IMC technique. They were decoupled completely and could be adjusted independently, which avoided the undesirable influence on performance of the primary controllers. The main controller in the primary loop was devised as a PID using the method of minimum sensitivity, which could guarantee not only the nominal performance but also the robust stability of the system. A setpoint filter was added in the primary loop to improve the tracking performance. All the controllers of the two closed-loops were designed analytically, and could be adjusted and optimized by single parameter respectively. Simulations were carried out on three various processes with time delay, and the results show that the proposed method can provide a better performance of both set-point tracking and disturbance rejection and robustness against parameters perturbation.