Sliding mode control for systems subjected to unmatched disturbances/unknown control direction and its application

This article investigates the control issue for systems subjected to unmatched disturbances and unknown control direction simultaneously. A class of adaptive nonlinear disturbance observer is developed to estimate the unmatched disturbances precisely and then extended to the general high-order form. The proposed method guarantees the stability of the second-order and high-order system under unknown control direction and robustness against the unmatched disturbances with the help of the sliding mode technique. The application in the integrated missile guidance and control (IGC) system design demonstrates the validity of the proposed control method. Herein, the cause of unknown control direction and the influence of the time-vary control gain on the missile are discussed in detail. Also, the Monte Carlo campaign is run to show the superiority of the developed control strategy compared with the existing IGC method.