Design of a global discrete-time sliding mode control scheme for a class of nonlinear systems with state delays and uncertainties

This paper proposes a discrete-time sliding mode control design for a class of discrete-time dynamic systems with time delays, parameter uncertainties, and external disturbances. The robust design implements an adaptive discrete-time reaching law in order to reduce the effect of the chattering phenomena and improve system robustness. It also considers a lumped disturbance function for the unknown parameters and time-delayed terms in order to estimate both at the same time. Additionally, the proposed sliding function ensures that the states of the control system are put on the switching surface right from the beginning, thus eliminating the reaching phase. The effectiveness of the proposed scheme was assessed using the longitudinal and lateral dynamics of an Osprey plane model. The obtained results indicated that the proposed approach guarantees system stability and ensures excellent tracking performance in the simultaneous presence of time delays, parameter uncertainties, and external disturbances.