Design of structural optimal robust controller

The traditional robust controller is designed to meet the requirement considering both the disturbance and the plant uncertainty while the controller uncertainty is always neglected. The structural optimal robustness of the closed-loop system is proposed based on the analysis of the robust radii of both the plant and the controller. The subspace angle is introduced to measure the "distance" of two subspaces, and its metric is equivalent to the gap metric. The optimal robust controller based on gap metric is designed to control the rate of the line of sight for an electromechancial target tracking system. It is shown from simulations that the optimal robust controller with the biggest robust radius is superior on the ability of disturbance rejection, and high tracking performance when additive uncertainty exists compared with the robust controller with smaller robust radius.