On the Choice of an Appropriate Reference Model for Control of Multivariable Plants

The choice of the reference model is the main task to be performed by the designer in a model reference control design. A poor choice of the reference model may result in a closed-loop performance that bears no resemblance to the one specified and may even be unstable. In this paper, we discuss this issue in the control of multiple-input multiple-output plants in the very typical case where a no plant model is available and the controller structure is defined a priori. Experimental results in a three-tank level control plant show how a naive choice of the reference model leads to very poor closed-loop performance. The problem is then analyzed, exposing the naivete of this design example and deriving the general guidelines for the effective choice of the reference model in multivariable systems. The application of these guidelines to the three-tank plant illustrates their effectiveness.