On the advantage of using explicit plant model information in the 2-DOF controller reference processing components

This communication deals with the problem of reference tracking by using a Two Degree of Freedom (2-DOF) control configuration and considering the effect of plant model mismatch. The analysis is based on the idea of performance degradation due to the presence of uncertainty and how this performance degradation can be reduced. The performance degradation is characterized for 1DOF as well as 2-DOF controllers. It is seen that the use of explicit plant model information on the second degree of freedom allows to distinguish between uncertainty that affects the feedback loop and the out-of-the loop controller. The solution proposed is an adaptive formulation of a 2-DOF controller where the part of the controller that operates inside the feedback loop is suggested to remain fixed whereas the reference processing components are adapted according to an identified plant model. The resulting scheme is proposed as an alternative to tackle the reference tracking problem despite the presence of uncertainty. Therefore the Robust Reference tracking problem.