A novel control scheme for typical unstable processes with time delay

In this paper, a new two-degree-of-freedom control structure is proposed for controlling unstable processes with time delay. The setpoint tracking is of open-loop control and therefore is decoupled with the load disturbance rejection, for which the controller is analytically designed in terms of H-2 optimal performance specification. Meanwhile a conventional proportional(P) controller is additionally employed to stabilize the setpoint response. By proposing the desired complementary sensitivity transfer function form of the inner closed-loop for the load disturbance rejection, the closed-loop disturbance estimator is inversely derived. It is a dominant merit that the time domain system response specification of the proposed control structure can be quantitatively estimated by virtue of the analytical design procedures developed for the controllers. Illustrative simulation tests are included to demonstrate the superiority of the proposed method.