STABILITY ROBUSTNESS OF LQ AND LQG ACTIVE SUSPENSIONS

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.