Detection of Oscillatory Control Loops in Irrigation Channels

In this paper the algorithm for detection of oscillatory control loops developed in Hägglund (1995) is applied to irrigation channels. The water levels in irrigation channels are controlled using mechanical gates. The controller configuration is a decentralized distant downstream scheme where a gate controls the water level upstream of the next downstream gate. The controller is a PI controller augmented with a low pass filter together with a feedforward term from the downstream gate. The algorithm is applied to real data from six consecutive reaches of an irrigation channel, and it detected the control loops that gave oscillatory response. Furthermore, due to the decentralized configuration, one is also able to localize the cause of the oscillation. Given that there can be many control loops in a channel network, the ability to localize the cause of an oscillation speeds up the trouble shooting process. However, care must be taken in choosing the thresholds in the algorithm in order to avoid frequent false alarm.