Hierarchical control of irrigation canals in the presence of disturbances: Framework and comparison

We study a control problem of delivering water to farmers through an irrigation canal and introduce a hierarchical controller with a Coordinator that by employing Model Predictive Control principles coordinates local canal reaches by modifying setpoints only when it is needed. Once the setpoints are set, the Coordinator does not interfere with the functioning of the local sites and the canal is fully controlled by local PI controllers located at each gate. Therefore the communication between the centralized controller and the local sites is kept minimal, which is motivated by the communication restrictions that are present in the field of irrigation. We consider three predictive control designs, namely a nominal controller, and two robust designs: a constraint tightening controller adapted to fit our application and a min-max controller. We present a numerical example to compare the performance obtained by the three controllers. It is found that for the given case study with a small disturbance realization, the nominal controller performs better than the robust controllers, the behaviors of which prove overly conservative.