Control of a Multivariable System Using Optimal Control Pairs: A Quadruple-Tank Process

This paper deals with one of the possible ways to control multivariable (MIMO) control loops. The suggested control design procedure uses the so-called primary controllers, auxiliary controllers, and also correction members. Parameters of the primary controllers are determined for the optimal control pairs using arbitrary single-variable synthesis methods; namely, the modulus optimum method, the balanced tuning method, and the desired model method. The optimal control pairs are determined using the so-called relative gain array tool or the relative normalized gain array tool combined with other tools, as the condition number or the Niederlinski index. The auxiliary feedback controllers serve for ensuring a control loop decoupling. Invariance to load disturbance of a control loop is realized by using the correction members. The novelty lies especially in the combination of the original inverted decoupling with disturbance rejection and provided tuning methods. The proposed control design for a MIMO loop is verified by simulation for the two-variable controlled plant of a quadruple-tank process and evaluated by using various criteria. Moreover, a numerical comparison to some other methods is given to the reader.