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Enhanced performance for two-degree-of-freedom control scheme for second order unstable processes with time delay

The present study suggested a modified disturbance estimator in a recently published two-degree-of-freedom control scheme for open-loop unstable process with time delay. A simple PID controller cascaded with lead lag filter replaces the high order disturbance estimator for enhanced performance. A new analytical method, which has only one tuning parameter, is developed for the design of the modified disturbance estimator. Several illustrative examples taken from previous works are included to demonstrate the superiority of the modified disturbance estimator. The results show the proposed disturbance estimator provides superior performance both in nominal and robust cases. The proposed method also has several important advantages for the process engineers in industries: it covers several class of unstable process with time delay in a unified manner; it is simple and easy to design and tune.