Robust FOPID Stabilization for Smith Predictor Structures

In this letter, an effective graphical tuning method of Fractional-Order Proportional Integral Derivative (FOPID) controllers is proposed for the Smith Predictor (SP) control structure. At first, necessary and sufficient conditions are achieved for the robust stability of the SP structure based on the zero exclusion principle. Then, by benefiting from the D-decomposition technique and the value set concept, the problem of robustly stabilizing the SP scheme is solved using FOPID controllers. Moreover, an auxiliary function is provided to enhance the performance of the SP structure by the sensitivity function. Simulation results successfully confirm the validity and effectiveness of the proposed method, which is provided in illustrative examples.