Variable structure system theory based disturbance identification and its applications

Based on the VSS theory, this paper presents a new method of estimating the disturbance for minimum-phase (with respect to the relation between the disturbance and output) continuous-time dynamical systems with arbitrary relative degrees. By using the transfer function method, first, the higher order filter of the disturbance is estimated, then, the lower order filter of the disturbance is estimated inductively. Eventually, the disturbance is estimated. The estimated disturbance is employed to construct a VSS-type state observer. Further, the estimated disturbance and the state observer are applied to a controller to place the desired stable poles and to cancel the disturbance. A design example and simulation results are presented to show the practicality and effectiveness of the proposed algorithm.