A novel fast terminal sliding mode control method based on immersion and invariance for course control of USV

Abstract

The course control of an unmanned surface vehicle(USV) with water-jet-propelled is addressed using a novel fast terminal sliding mode control approach based on system immersion and manifold invariant (FTSMC-I&I). The control scheme can ensure all error signals globally exponentially converge to origin in finite-time by the novel fast terminal sliding mode controller. In addition, I&I method is applied to design an adaptive disturbance estimator in order to improve estimation accuracy and convergence speed with respect to parametric uncertainties and disturbances that are encountered in sailing applications. Meanwhile, an additional compensation item is introduced into the adaptive law to keep the estimation error manifold invariant and attractive. As a result, the estimation error of disturbances tends to zero and its dynamic process can be adjusted. It is shown that the proposed method can guarantee the asymptotical stability and the finite time convergence of the system from Lyapunov stability analysis. Compared with the backstepping adaptive sliding mode control, the proposed control method can achieve higher precision and better robustness in the presence ofpractical input limits.