Nonlinear robust motion control of hydraulic servo system with matched and mismatched disturbance compensation

A novel disturbance observer-controller scheme for hydraulic servo system is proposed in this paper. Not only the matched disturbance but also the mismatched disturbance can be estimated by this scheme.A composite controller is synthesized by a backstepping procesure.And the estimation of the matched and mismatched disturbance was used in the contoller to compensate the corresponding disturbance. Especially, the estimation for mismatched uncertainties was used in the virual control law. The analysis of the estimation error was implemented along with the stability analysis of the controller. Theoretical analysis proves that the final tracking accuracy and the disturbance estimation accuracy can be guaranteed by the proposed disturbance observer-controller scheme Furthermore, the convergence of the closed-loop controller-observer system is achieved when the disturbance becomes to a constant. Extensive comparative simulation results demonstrate the effectiveness of the proposed observer-controller scheme.