A new nonlinear robust disturbance observer

This paper presents a new nonlinear robust disturbance observer by using on ly the input-output information for minimum phase dynamical systems with ar bitrarily relative degrees. The model uncertainties, the nonlinear parts of the system are merged into the disturbance term, and are regarded as a par t of the disturbance. The disturbance is assumed bounded. However, the uppe r and lower bounds are assumed unknown. The new disturbance observer is ins pired by the VSS control theory, whereas the upper and lower bounds of the disturbance are adaptively updated. The estimation error of the disturbance can be made as small as necessary by choosing the design parameters. The a ttraction of the proposed method lies in its robustness to disturbance and easiness to be implemented. Example and simulation results show the effecti veness of the proposed algorithm. (C) 2000 Elsevier Science B.V. All rights reserved.