On weight adjustments in H∞ control design

H∞ control design is generally performed iteratively. At each iteration, the weights constraining the desired closed-looptransfer functions are adjusted until satisfactory performance margins are obtained. The way in which the weights are adjusted is generally heuristic and based solely on past experience and engineering judgement/intuition. It is consequently important to understand and provide guidelines on how weight adjustments directly affect the synthesised controller, and more importantly, the corresponding closed-loop transfer function matrices. This article presents a thorough study of this problem based on small weight adjustments in H∞ control design.