Design of Model Predictive Controller for a Four-Tank Process Using Linear State Space Model and Performance Study for Reference Tracking under Disturbances

Chemical plants are tightly integrated processes, which exhibit nonlinear behaviour and complex dynamic properties. For decades, the chemical process industry has relied on single-loop linear controllers to regulate such systems. The multivariable four-tank system exhibits complex dynamics, which includes interaction, transmission zero, and non-minimum phase characteristics that emerge from a simple cascade of tanks. The linearised dynamics of the system have a multivariable zero that is possible to move along the real axis by changing a valve. The zero can be placed in both the left and the right half-plane. The four-tank process is ideal for illustrating many concepts in multivariable control. In this paper, a linearised state-space model of the four tank process was developed in the non-minimum phase region and a model predictive controller was designed using this model. The performance of this set up was studied for reference tracking and disturbance rejection cases.