Abstract of Thesis presented at COPPE/UFRJ as a partial fulfillment of the requirements for the degree of Master of Science (M.Sc.)

Modeling and Control Level of the Quadruple-Tank Process

José Alberto Naves Cocota Júnior

September/2009

Advisors:

Ramon Romankevicius Costa Alessandro Jacoud Peixoto

Department:

Eletrical Engineering

      This paper deals with modeling, parameter identification and level control of a four coupled tanks. A model is obtained by applying the principle of mass conservation together with the Bernoulli's equation. The nonlinear model is analyzed and validated by comparison with experimental results. The system may present nonminimum phase behavior depending on the flow distribution of the water pumped to the tanks. Upon linearizing this model, one can observe that the system presents a multivariable real zero that can assume either negative or positive values. Therefore, the four tanks system is ideal to illustrate several concepts related to multivariable control, in particular the performance limitations due to multivariable right half-plane zeros. A decentralized control structure is proposed and independent control-loop tuning is performed. In the case where the system shows nonminimum phase behavior, an appropriate pairing of control and process variables may be necessary as shown by their interaction analysis, otherwise the closed-loop plant may lead to instability. Finally, simulation and experimental results with the proposed control are compared.