Adaptive nested terminal sliding mode control for a hypersonic vehicle with mismatched uncertainties

Abstract

This paper tackles the tracking control of flexible hypersonic vehicle (FHV) with mismatched uncertainties by utilizing the adaptive nested terminal sliding mode control method. The controllers of velocity loop and altitude loop are designed separately based on the control-oriented model which is obtained by simplification of the FHV model. It's noted that the previous sliding mode control is sensitive to mismatched uncertainties, which weakens the use of sliding mode strategy. Therefore, the nested terminal sliding mode control is applied in FHV, to provide a virtual control in every step until the real control law is obtained, which can deal with the mismatched uncertainties problem and achieve finite-time stability. What's more, the lumped uncertainties including the derivative of virtual control law are estimated by adaptive algorithm, which can solve the problem of “explosion of complex” and the upper bounds of uncertainties are not required to be known in advance. Simulation results show that the proposed control method can guarantee the accurate tracking of velocity and altitude effectively.