Improved sliding mode control of a class of nonlinear systems: Application to quadruple tanks system

In this paper, a stable adaptive sliding mode based on tracking control is developed for a class of nonlinear Multi Input Multi Output (MIMO) systems with external disturbances. In order to reduce the chattering phenomenon without deteriorating the tracking performance, the discontinuous term in the conventional sliding mode technique is replaced by an adaptive Proportional derivative (PD) term. The effect of the approximation error which arises from the PD term is reduced by adding a robust term in the proposed control law. All parameter, adaptive laws and the robust control term, are derived based on the Lyapunov stability analysis. The overall adaptive sliding mode scheme guarantees the convergence to zero of tracking errors and the boundedness of all signals in the closed-loop system. The proposed approach is applied to a quadruple tanks system and achieves satisfactory simulation results.