ROBUST PERFORMANCE WITH RESPECT TO BLOCK DIAGONAL INPUT UNCERTAINTY

We consider the robust performance problem of maintaining the output sensitivity function small despite the presence of block diagonal uncertainty at the plant input. For the case of two blocks of uncertainty, we study this problem by analyzing bounds upon the structured singular value. It is shown that the potential difficulty of attaining robust performance is primarily determined by the difficulty of maintaining a set of interaction parameters small. We derive a robustness indicator which is useful in detecting this potential difficulty. The indicator is a function of both the plant condition number as well as its input directionality properties.