Research ArticleOn oscillation reduction in feedback control for processes with an uncertain dead time and internal-external disturbances

- The oscillation due to model mismatch in Smith Predictor is greatly reduced.
- The conditional feedback is introduced in Smith Predictor.
- Model information is incorporated into the ADRC for better disturbance rejection.
- A practical tuning procedure is given for practitioners.
- Extensive simulation studies show much stronger performance robustness.

This paper aims to find a practical solution to reduce oscillation on the Smith Predictor (SP) based design with the dead time (DT) uncertainty, making it less sensitive to DT change and more effective in disturbance rejection. First, a conditional feedback mechanism is introduced in SP to reduce the amount of oscillation caused by the model inaccuracies in the DT parameter. Then, to address the oscillation caused by the phase lag in traditional PI controller and uncertain dynamics, this conditional SP is combined with active disturbance rejection control (ADRC), assisted by the knowledge of process dynamics. A practical tuning method is provided for the practicing engineers. The proposed approach is validated in extensive simulation studies with different types of plants and in frequency domain analysis. The simulation results show significant improvements in performance robustness and transient response.