Fast and smooth adaptive second-order sliding mode control for hypersonic vehicles

To solve the problem of severe matching/non-matching uncertainty of hypersonic vehicles in the process of climbing, a new adaptive super-twisting sliding mode control method was proposed to suppress the matching uncertainty of the ascent phase, and the method was combined with a sliding mode differentiator to resolve the non-matching uncertainty of the ascent phase. Firstly, the sliding mode differentiator was used to estimate the derivatives of the velocity and height in the feedback linearization model to narrow the gap between the feedback linearization model and the original model. Secondly, on the basis of the traditional super-twisting sliding mode, a linear term was added to increase the convergence speed. Then, the discontinuous symbolic functions in integral terms were made continuous to ensure the smoothness of the control input, which eliminated or attenuated the chattering to a greater extent. Lastly, since the upper bound of the composite disturbance was unknown, an adaptive law was designed to ensure that the parameters were not overestimated and the initial value could be chosen to ensure the convergence speed. Simulation results show that the improved control method can meet the control requirements, and compared with the traditional super-twisting sliding mode control algorithm, the improved control method had smoother control input and faster convergence speed, which verifies the effectiveness and advancement of the proposed method. © 2020, Editorial Board of Journal of Harbin Institute of Technology. All right reserved.