DESIGN OF GLOBAL CONTROL ALGORITHM FOR IRRIGATION CANALS

The problem of irrigation canal regulation under demand delivery opera tion was formulated as an optimal control problem. To apply the linear optimal control theory, the Saint-Venant equations of open-channel fl ow were linearized using the Taylor series after using a finite-differ ence approximation on the original nonlinear, partial differential equ ations. A proportional-plus-integral (PI) controller was developed usi ng the concepts of linear optimal control theory. Since the order of t he controller gain matrix was large, an optimal observer (Kalman filte r) was designed to estimate values for the variables that were not mea sured. An example irrigation canal with five pools was considered. Wit h the finite-difference technique used, there was a total of 45 state variables and five control variables (gates) in the problem. With two measurements per pool, values for 35 state variables were estimated us ing the observer. By subjecting the canal to random disturbances of up to 40% of the initial inflow rate into the canal, the simulated perfo rmance of the global feedback control algorithm along with the Kalman filter was found to be acceptable in terms of achieving either a const ant-volume control or a constant-level control in the canal pools in t he presence of random disturbances in lateral flow rates.