On the order reduction of LQG designed controllers

LQG procedures for controller design yield compensators of the same order of the plant. However, practical design considerations often dictate low order controllers. This paper presents a procedure which allows the reduction of these high order LQG designed controllers to low order ones. The proposed controller reduction method is based on the same performance index J used while designing the optimal regulator. The proposed method ensures that the value of J for the system with the reduced order controller is essentially identical to the value obtained with the full order controller. Numerical results are presented which illustrate the effectiveness of the method.