A new interpretation of the LQG/LTR technique using optimal projection equations

It is demonstrated that the LQR/LTR (linear quadratic Gaussian/loop transfer recovery) technique can be viewed as a way to achieve robustness even under the constraint of a reduced-order controller, even though one is not necessarily recovering a desired transfer function asymptotically. The optimal projection equation (OPE) approach gives an expanded view of LQG/LTR technique when the order of the controller is intentionally less than the order of the system design model. Also, the OPE approach allows other forms for Ω, which may give more flexibility as to how the system perturbations are modeled, to be chosen