qIt is interesting to note that the margins deteriorate
as control weight (1/q) gets small (large q) and/or system driving noise gets
large (large s). In modern control
folklore, these have often been considered ad hoc means of improving
qH2(LQG) controllers have no global
qImprove the robustness of a given design by
relaxing the optimality of the filter with respect to error properties.
LQG loop transfer recovery (LQG/LTR) design technique. The idea is to
design a filtering gain in such way so that the LQG (or H2) control law will approximate the loop properties of the
regular LQR control.