Robust Fractional Order Control of a Pool of a Main Irrigation Canal in Submerged Flow Condition

Abstract

This work addresses the robust control of a pool of a main irrigation canal working in a submerged flow condition. A laboratory prototype of hydraulic canal at the University of Castilla-La Mancha is used in this study. A series connection of a non-linear static block and a linear first order plus time delay system is proposed to model the dynamics of such process for all the considered operating regimes. The gain variations in function of the operating regimes are counted and corrected by using a gain scheduling block that inverts the before nonlinearity. However, a residual gain variation remains, whose effect is corrected by a fractional-order proportional integral PI controller that is robust to process gain changes. Such controller is tuned to make the closed-loop system fulfill two temporal specifications: (a) a desired overshoot, obtained defining an equivalent phase margin frequency specification and (b) a desired settling time, obtained defining an equivalent gain crossover frequency specification. Moreover, a third specification is defined: the isophase margin condition, which accounts for the changes in the gain. The simulated results of our canal show the adequate performance of this control system.