Multivariable control of a temperature process with a continuously stirred tank

Control of a continuously stirred tank (CST) is a benchmark process control problem, which can be utilized to describe and suggest control solutions to many industrial and domestic temperature processes. The current research idea is using a CST as a blender for cold and hot water through two control valves escorted with a pump to achieve a desired temperature and flow rate at the outlet of a domestic shower system. The process control system is in multivariable (MV) structure with three control inputs and two outputs. The control goal is to track the set points and maintain stable, smooth and minimum-overshoot responses despite perturbations of each inlet including temperature and flow variations. In current research, the system dynamic mathematical model is developed. The MV system is linearized to make the elimination of loop interaction easier. In closed loop, two sub-processes of temperature and flow rate are controlled using fuzzy logic self-tuning proportional integral derivative (PID) control and fuzzy logic control (FLC) with a proportional gain, respectively. Performance of proposed control mechanism and decoupler is tested via a number of simulations. Performance of proposed MV control system is tested with respect to reference and disturbance variations. Proposed MV control system tracks the reference point and gives good system stability and performance in rejecting disturbances.