UDE-based 2-DOF control design for Input/Output delay system

This paper proposes a compound feedforward and uncertainty and disturbance estimator (UDE) based control strategy for uncertain systems with Input/Output time delay. The conventional UDE is modified to accommodate the time-delay characteristics. The major aims and modifications of the new structure are: i) to avoid the negative effects of the measurement delay, the predicted process output is calculated based on the Taylor series expansion and then sent into UDE; ii) to synchronize the UDE and the plant, the control signal is delayed by an equivalent input dead time before importing into UDE; and iii) to obtain fast tracking performance, the feedforward concept is adopted, which is, however, determined by the feedback law for a virtual plant. Then the error feedback is based on the outputs of the real plant and the virtual plant. The robustness and disturbance rejection goes to the responsibility of a filter and the error feedback. Simulation results demonstrate the effectiveness and robustness of the proposed strategy.