Composite chattering-free discrete-time sliding mode controller design for active front steering system of electric vehicles

In order to reduce the adverse effects of internal uncertainty and external disturbance in the active front steering (AFS) system of electric vehicles, two chattering-free discrete-time sliding mode (CDSM) AFS controllers are proposed in this paper. First of all, the sideslip angle is estimated by constructing a Luenberger observer and a two-degree-of-freedom model-based parameter tuning scheme is proposed to simplify the parameter tuning. On this basis, the first-order disturbance difference is imposed on the CDSM controller to reduce the disturbance estimation error. Secondly, in order to further improve the control accuracy, a generalized proportional integral observer (GPIO) is constructed and its stability is verified by the algebraic equations. Finally, a new composite CDSM controller is obtained with the aid of GPIO to further improve the control performance. The feasibility and effectiveness of the proposed methods are verified by simulations.