Guidance-error-based robust fuzzy adaptive control for bottom following of a flight-style AUV with delayed and saturated control surfaces

This paper addresses the problem of robust bottom following control for a flight-style autonomous underwater vehicle (AUV) with both delayed and saturated control surfaces by using a pair of rudders. First, the time-delayed dynamics of rudders is considered, which renders a high-order nonlinear dynamics analysis and design in the model-based backstepping controller by utilizing guidance errors; Second, to overcome the shaking control behaviour resulted by the model-based high order derivative calculation, a fuzzy approximator-based modelfree controller is proposed, in order to online approximate the unknown part of the ideal backstepping architecture. In addition, the adaptive error estimation technology is resorted to compensate the system approximation error, ensuring that all the position and orientation errors of robust bottom following control tend to zero; Third, to further tackle the potential unstable control behaviour from inherent saturation of control surfaces driven by rudders, an additional adaptive fuzzy compensator is introduced, in order to compensate control truncation between the unsaturated and saturation inputs. Subsequently, Lyapunov theory and Barbalat lemma are adopted to synthesize asymptotic stability of the entire bottom following control system; Finally, comparative numerical simulations among the model-based benchmark controller, the unsaturated and saturated model-free controllers are provided to illustrate adaptability and robustness of the proposed bottom following controller for a flight-style AUV with delayed and saturated control surfaces