Order reduction of linear-quadratic-Gaussian-designed controllers

Linear-quadratic-Gaussian (LQG) procedures for controller design yield compensators of the same order as the plant. However, practical design considerations often dictate low-order controllers. This paper presents a procedure for reducing the order of LQG-designed controllers. The proposed method is based on the same performance index J used for designing the optimal regulator; the value of J for the system with the reducedorder controller is essentially identical to the value obtained with the full-order controller. It is shown that the observer normal coordinates play an important role in the proposed method. The numerical results presented illustrate the effectiveness of this method.