Adaptive fuzzy sliding mode control for robust trajectory tracking control of an autonomous underwater vehicle

In this study, a robust and adaptive tracking control is designed for a complete nonlinear model of an autonomous underwater vehicle. The tracking control is accomplished by proposing an adaptive fuzzy sliding mode control (AFSMC) scheme. Firstly, the fuzzy control rules are derived using the Lyapunov energy function to minimize the chattering in the control signal, which is commonly appeared in conventional sliding mode control. Furthermore, an adaptive control law is obtained to adapt the fuzzy consequent parameter of a fuzzy logic controller which enhances the stability of the whole system. Simulations were carried out under different sets of reference trajectories to test the potency of the AFSMC. The proposed method not only eliminates the problem of chattering but also reduces the steady-state errors in tracking control. In addition, due to adaptive control law, the proposed AFSMC is effective in adapting the unknown lumped uncertainty acting on the vehicle dynamics.