Linear matrix inequality-based approaches for H-infinity control synth
esis for systems with weighting functions possibly face numerical ill-
conditioning and heavy computation. In this paper, by exploiting the p
otential pole/zero cancellation (mostly modes of weighting functions)
in the closed-loop system, a new formulation is presented to find a fu
ll-order controller via reduced-order LMIs (linear matrix inequalities
) and fewer decision variables. As a result, both numerical conditioni
ng and numerical efficiency are improved. In addition, the new formula
tion is directly applicable to servomechanism problems where unstable
disturbance dynamics are appended for robust regulation.