Providing robust-adaptive fractional-order sliding mode control in hybrid adaptive cruise control systems in the presence of model uncertainties and external disturbances

This paper deals with the stabilizing of hybrid adaptive cruise control (ACC) systems in the presence of external disturbances and model uncertainties. Considering that upper bound of model uncertainties and external disturbances is a nonlinear function of ACC system states with unknown coefficients, a new robust-adaptive fractional-order sliding mode controller (RAFOSMC) is developed. The unknown coefficients of the functional upper bound of perturbations are obtained via some stable adaptive rules. Stability proof of the proposed RAFOSMC is presented based on Lyapunov theorem. It is also analytically shown that the proposed FOSMC has better performance than ordinary integer-order sliding mode controllers (IOSMC). Using FOSMC benefits a significant reduction in chattering and also faster convergence to the vehicle's safe distance in the vehicle's initial movement. Finite-time convergence of system states to the fractional sliding surface is then obtained, and a new approximation of sign function for more chattering elimination is also proposed in this paper. Simulation results and presented comparisons at the end of this paper show the effectiveness of the proposed methodologies.