Smooth backstepping sliding mode control for missile attitude system based on parameters online adjusting and estimating for square of disturbance upper bound

To efficaciously eliminate the effect of chattering caused by parametric uncertainties and external disturbances on attitude tracking control of missile systems, a chattering-free backstepping sliding mode controller based on parameters online adjusting and square of disturbance upper bound estimating is proposed in this paper for the quaternion-described missile model, which is nonlinear in aerodynamics. The controller comprises the back stepping sliding mode strategy and several adaptive laws. First, one adaptive law is applied to adjust the uncertain parameters, involving inertias, atmospheric moment coefficients, and steering efficiencies online, which reduces the upper bound of the equivalent disturbances. Then, another adaptive law, estimating square of the disturbance upper bound, is introduced. Combining with the backstepping sliding mode controller, the expected missile attitude can be tracked asymptotically. Compared with other missile attitude controllers, key innovation of the proposed control laws are that the controller is based on the novel online adjusting model rather than the conventional fixed-parameter reference model and square of disturbance upper bound is estimated rather than the upper bound itself, which thoroughly abstains the chattering problem. Simulation results of a specific missile model demonstrate that the proposed controller is independent of the parametric uncertainties and can achieve a fast convergence rate without any chattering.