A Comparative Study of Linear and Nonlinear MIMO Feedback Configurations

In this paper, we compare several feedback configurations which have appeared in the literature (e.g. unity-feedback, model-reference, etc.). We first consider the linear time-invariant multi-input multi-output case. For each configuration, we specify the stability conditions, examine the relation between achievable I/O maps and the achievable disturbance-to-output maps, and study the effect of various subsystem perturbations on the system performance. In terms of these considerations, we demonstrate that one of the configurations considered is better than all the others. The results are then extended to the nonlinear multi-input multi-output case.