Loop transfer recovery for nonstrictly proper plants

Observer-based controllers for loop transfer recovery of nonstrictly proper systems which are left invertible and of minimum phase are considered. A complete analysis of the loop transfer recovery problem using either a full or a reduced-order observer-based controller is provided. A case is considered in which the uncertainties are modeled at the input point of a nominal plant model, and hence the required loop transfer function is specified at the plant input point. However, the results can be dualized for the case when the required loop transfer function is specified at the output point