The performance enhancement of a reverse osmosis (RO) unit through periodic control is studied by manipulating the feed pressure and the flow rate. To ensure the periodic behavior of the inputs, the manipulated variables (MV) are transformed into sinusoidal functions. In this case, the amplitude and the period of the sinusoidal functions become the surrogate MV and are regulated via nonlinear model predictive control algorithm. It was clear from the simulation results that the control system can generate cyclic inputs necessary to enhance the closed-loop performance by increasing the permeate production and lowering the salt concentration. The proposed control system can achieve its objective with arbitrary set point for the controlled outputs. It is important to note that reliable results were obtained even in the presence of modeling errors.

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