A comparative study of linear and non-linear MIMO feedback configurations

The paper compares several feedback configurations that have appeared in the literature (e.g. unity-feedback, model-reference, etc.). It first considers the linear time-invariant multi-input multi-output case. For each configuration, we specify the stability conditions, the set of all achievable I/O maps and the set of all achievable disturbance-to-output maps. The effects of various subsystem perturbations on the system performance are studied. In terms of these considerations, it is demonstrated that one of the configurations considered is better than all the others. The results are then extended to the non-linear multi-input multi-output case.