Tracking Performance and uncertainty: Performance Degradation Equivalence between 1-DOF and 2-DOF control configurations

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 with respect to the achieved nominal performance is characterized for 1-DOF as well as 2-DOF controllers. It is shown that this degradation is completely determined by the feedback controller and exhibits exactly the same expression for both 1-DOF and 2-DOF compensators. Therefore raising the question of apparent advantage of 2-DOF configurations where model uncertainty is considered.