Robustness Analysis of Dynamic Observers

Abstract It is shown that the open loop observers proposed in the literature are nonrobust devices since they cannot tolerate the slightest variation in parameter. If parameter variations are to be permissible, it is shown that the observer must be constructed as a closed loop (i.e., driven by error signals) device, which, however, is required to contain explicitly an exact, perturbation-free replica of the system being observed. One serious consequence of these results is that they emphasize the stringent accuracy requirements on both models and hardware that must be met before an observer can be considered for use in a control system.