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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.
Date of Conference: 20-22 July 2011