Singular perturbation method for reducing the model order in optimal control design

The optimal control for a high-order model of the plant is approximated by some functions obtained from two low-order models, the second being the sensitivity model of the first. The resuiting system is optimally sensitive with respect to the change of model order. The method is aimed at improving the "low-order design" in critical cases when the plant order is too high for the iterative optimization procedures to be practical.