LAUSR

Dear editor, Sliding mode control (SMC) is an effective control strategy that has been widely studied during the past decades. Compared with other control methods, SMC has strong robustness for external disturbances and plant uncertainties [1]. In general, conventional SMC is only sensitive to matched disturbances and cannot attenuate mismatched disturbances in an effective manner. To solve this problem, a quasi-continuous higherorder sliding mode control method was designed for systems with mismatched perturbations based on the backstepping techniques in [2]. Ref. [3] proposed an SMC approach for systems with mismatched uncertainties. Nevertheless, the condition limt→∞ ḋ(t) = 0 must be satisfied to enforce an asymptotical stability of the closed-loop system. To overcome the problem of mismatched disturbances, Ref. [4] investigated the SMC for a mismatched uncertain high-order system using an extended disturbance observer, and adaptive neural network dynamic surface control was discussed by introducing radial basis function neural networks in [5]. However, both control methods can ensure the convergence of tracking errors to a small residual set.