The structure of robust disturbance rejection control

This paper deals with the problem of disturbance rejection under state feedback in linear multivariable control systems. This problem is ill posed under arbitrary state space parameter perturbations. However, it is shown that with respect to arbitrary perturbations of the plant transfer function coefficients, a robust solvability condition and possibly a robust synthesis can be obtained. These results are significant because the class of arbitrary state space parameter variations is too rich for practical interest, whereas the more restricted class of arbitrary variations in transfer function coefficients more closely represents the realistic problem of engineering concern.