Abstract: For a system with inverse response to time delay, we propose a two-degreeof-
freedom (2-DOF) control method by combining the Smith predict or control with the
internal model control (IMC). The structure of Smith predict or control is used to obtain a
set-point tracking controller for good set-point tracking performance. In addition, a disturbance
rejection controller uses the method of internal model control to improve disturbance
rejection performance and robustness, overcoming the drawback of the traditional Smith
predictor. The transfer function of the process model is decomposed in to a minimum
phase part and a non-minimum phase part using direct decomposition and full decomposition
methods. Thus, two different methods for controller design are derived. Necessary and
sufficient conditions for the system robust stability are discussed. Theoretical analysis and
simulation results show that the proposed method has good set-point tracking response,
disturbance rejection response and robustness.

Key words: inverse response, two-degree-of-freedom control, Smith predictor control, internal model control