การควบคุมแบบโกลบอลลีลิเนียร์ไรซิ่งสำหรับควบคุมพีเอชของกระบวนการบำบัดน้ำเสีย / นันทนา ศิริพันธ์ = Globally linearizing control for pH control of the wastewater treatment process / Nantana Siripun
Several chemical industrial plants such as electroplating and metal finishing plants have used strong-acids and strong-bases in the production lines which need to be treated in a wastewater system to achieve the compliance with the standard of Industrial Department requirement. The pH control of a wastewater treatment process is one of the most challenging control problems because of high nonlinearity and time-variant of pH value during pH titration. A conventional PID controller and an on-off controller are rarely able to handle this nonlinearity resulting in poor control performances. Therefore, advanced control techniques are needed to cope with the pH control problem. This research presents the implementation of Globally Linearizing Control (GLC) together with an extended Kalman filter to control pH of the wastewater treatment process that is a part of an electroplating plant. The GLC, one of advanced model-based control techniques, has been developed to be applied to deal with both SISO or MIMO nonlinear process systems. Since the GLC is a model based control technique, it needs measurements and values of states and parameters which are neither all measurable nor known exactly. Therefore, the extended Kalman filter has been applied to estimate unavailable or unknown states and parameters and these estimates are incorporated in the control action determination in the GLC algorithm. Simulation study based on a written MatLab computer program is carried out in the presence of disturbances as well as plant/model mismatch. Simulation results have shown that in a nominal case, the GLC is able to control the pH of the system to a desired set point and its control performance is equivalent to the PID one. In the presence of plant/model mismatch, the GLC is still able to handle this mismatch and gives a good control performance whereas the PID gives a poor control response; the GLC is much more robust than the PID.
