In this research, the decentralized control of an Activated Sludge Process (ASP) with the modern Proportional-Integral Derivative (PID) controller tuning techniques is discussed. This tuning technique provides the entire closed loop stabilizing set for a dynamic process. Recent extensions in this algorithm are used to find stability margins feasible from the stabilizing set. The ASP model considered here is a multivariable four-state non-linear model and is linearized to a Two Input Two Output process for control purposes. The input-output pairs are selected by ignoring interactions in the process and the controllers are tuned for these individual control loops. The designed controllers are simulated with the additive process interactions and with the nonlinear model to discuss the effects on designed closed loop stability margins.
The closed loop stabilizing sets are obtained, and the necessary design requirements are specified. Frequency responses for models with and without interactions, and with the non-linear model are compared to validate the design. The models are also subjected to the disturbances to check the performance of controllers. Finally, the design is compared to a multivariable controller to show advantages of using this design methodology for this process
