A two-degree-of-freedom control scheme for improved performance of unstable delay processes

A two-degree-of-freedom control scheme is proposed for enhanced control performance of unstable processes with time delay. The two controllers in the scheme are well placed to tune from the setpoint and disturbance. The design steps of these two controllers are independent. The H₂ optimal control method is used to design the set-point tracking controller and an optimal internal model control (IMC) filter structure is proposed to design a proportional-integral-derivative (PID) controller that produces an improved disturbance rejection response. The setpoint and load disturbance responses can each be tuned conveniently by a single control parameter. Especially, improvement of disturbance response is extremely great compared with recently reported methods. Illustrative examples show the simplicity and superiority of the proposed controller design method over previously published approaches both for the setpoint response and for the load disturbance rejection.