Linear Active Disturbance Rejection Control for Processes with Time Delays: IMC Interpretation

This paper investigates linear active disturbance rejection control (ADRC) for processes with time delay. In the past years several modified active disturbance rejection control methods, including Smith predictor based ADRC (SP-ADRC), predictor observer based ADRC (PO-ADRC) and delayed designed ADRC (DD-ADRC) have been proposed to tackle systems with time delay. In this paper it is shown that these modified ADRCs can be interpreted in the framework of a two-degree-of-freedom (TDOF) internal model control (IMC), so the analysis and design can all be done via the well-known IMC framework. With the aid of the TDOF-IMC framework, the three modified ADRCs are compared and some interesting conclusions are drawn. Analysis and simulation results show that PO-ADRC structure is the best delay compensation structure among the three methods. However, the overall performance of the three methods will also depend on the tuned parameters, and the robustness measure is helpful in tuning the parameters to achieve compromise in performance.