DEVELOPMENT OF A SUPERVISORY CONTROL STRATEGY FOR THE OPTIMAL OPERATION OF GRAIN DRYERS

In spite of the importance and especially high energy demands of grain dryers, relatively few studies have been carried out to discover the optimal conditions for their operation. High performance operation can only be achieved if an adequate operating strategy is developed. For its implementation, a reliable control structure is required, and some of the limitations of the conventional control strategies normally us ed in dryers are observed. These strategies are SISO; the control norm ally used presents low performance and the disturbance is characterize d by several amplitudes and frequencies. A possible way to minimize th is difficulty consists of defining the multilevel structure such that each level acts at a given amplitude and frequency. In order to implem ent this multilevel structure, an optimization problem was developed t o function as a supervisory control and a predictive algorithm (DMC) w as used for servo or regulatory control. The proposed DMC algorithm pr esented satisfactory results for the load rejection and set-point vari ation, only when a small disturbance was applied. For a larger disturb ance an optimization procedure was necessary. The routine efficiently maintained the optimal operational conditions of the dryer and could b e used in the supervisory control of the system.