Output feedback adaptive robust control of uncertain linear systems with large disturbances

Discontinuous projection based adaptive robust control (ARC) is extended to a class of uncertain linear systems with large disturbances. An observer is first designed to provide exponentially convergent estimates of the unmeasured states. This observer has an extended filter structure so that online parameter adaptation can be utilized to reduce the effect of the possible large nominal disturbance that has a known shape but unknown amplitude. Estimation errors are dealt with via robust feedback at each step of the design procedure. Compared to other existing robust adaptive schemes, the proposed method explicitly takes into account the effect of disturbances and uses both parameter adaptation and robust feedback to attenuate its effect for an improved performance. Furthermore, the upper bound on the absolute value of the tracking error over the entire time-history is given and related to certain controller design parameters in a known form, which is more transparent than that in RAC design