Design of discrete quasi-sliding mode controllers with perturbation estimation

In this paper, the design of discrete quasi-sliding mode controllers is proposed for a class of MIMO nonlinear discrete time systems without the knowledge of the upper bound of perturbations in order to solve the tracking problems. The designing process of the proposed controllers contains three parts. The first part is the design of sliding function. The second part is to design controllers such that the discrete sliding condition can be satisfied. The last part is to estimate the perturbations if they exist. The previous information of perturbation can be obtained, and is utilized to estimate the present perturbation. The robustness of system´s stability is guaranteed, and the tracking accuracy can be increased by utilizing more previous information of perturbations, or by increasing the sampling rate