Ag. Ulsoy et al., STABILITY ROBUSTNESS OF LQ AND LQG ACTIVE SUSPENSIONS, Journal of dynamic systems, measurement, and control, 116(1), 1994, pp. 123-131
A two-degree-of-freedom quarter-car model is used as the basis for lin
ear quadratic (LQ) and linear quadratic Gaussian (LQG) controller desi
gn for an active suspension. The LQ controller results in the best rms
performance trade-offs (as defined by the performance index) between
ride, handling and packaging requirements. In practice, however, all s
uspension states are not directly measured, and a Kalman filter can be
introduced for state estimation to yield an LQG controller. This pape
r (i) quantifies the rms performance losses for LQG control as compare
d to LQ control, and (ii) compares the LQ and LQG active suspension de
signs from the point of view of stability robustness. The robustness o
f the LQ active suspensions is not necessarily good, and depends stron
gly on the design of a backup passive suspension in parallel with the
active one. The robustness properties of the LQG active suspension con
troller are also investigated for several distinct measurement sets.