Subspace controller design to the mixed H2/H∞ synthesis with uncommon LMI solutions

This paper proposes an interesting technique for LMI-based synthesis of mixed H₂/H_∞ controllers that has the potential to avoid some of the inherent conservatism of current LMI methods. Here we obtain smaller-size LMI formulas which are similar to "elimination procedure of variables (EPV)" but partially retains the controller variables, although they are completely eliminated in EPV. It enables us to carry out "change of variables (CV)" for control design in a subspace. Eventually, jointly convex LMI formulas for the mixed problem are established, which allows for uncommon LMI solutions.