New approach to design a nonlinear PI controller for a CSTR system

In this paper, a new approach is proposed to tune a proportional –integral (PI) controller. By conceptual analyzing the operations of the proportional and integral parts of the controller, the design procedure is developed. Because of using nonlinear functions to tune the controller coefficients, the controller is categorized as a nonlinear PI controller. The proposed idea for tuning the PI controller includes the two steps. First, the proportional coefficient is tuned to increase the speed of the plant response. To achieve this objective, the control signal is set at maximum level for all error values larger than a pre-specified value. Second, the integral coefficient is tuned to decrease the overshoot of the plant response. To get this objective, the integral part of the controller is eliminated when the error is big. To validate the proposed idea, a highly nonlinear plant, named Continuous Stirred Tank Reactor (CSTR) is controlled by the nonlinear PI controller. A classical linear PI controller and a neurocontroller are selected for comparison. Simulation results and comparisons show the priority of the proposed nonlinear PI controller to achieve faster response with least overshoot.