Cs. Zhang et My. Fu, A REVISIT TO THE GAIN AND PHASE MARGINS OF LINEAR-QUADRATIC REGULATORS, IEEE transactions on automatic control, 41(10), 1996, pp. 1527-1530
Citations number
13
Categorie Soggetti
Controlo Theory & Cybernetics","Robotics & Automatic Control","Engineering, Eletrical & Electronic
In this paper, we revisit the well-known robustness properties of the
linear quadratic regulator (LQR), namely, the guaranteed gain margin o
f -6 to +infinity dB and phase margin of -60 degrees to +60 degrees fo
r single-input systems. We caution that these guaranteed margins need
to be carefully interpreted. More specifically, we show via examples t
hat an LQR may have a very small margin with respect to the variations
of the gain and/or phase of the open-loop plant. Such a situation occ
urs in most practical systems, where the set of measurable state varia
bles cannot be arbitrarily selected. Therefore the lack of robustness
of the LQR can be very popular and deserves attention.