Adaptive μ -modification control for a nonlinear autonomous underwater vehicle in the presence of actuator saturation

This paper deals with adaptive control of a nonlinear autonomous underwater vehicle (AUV) in the presence of actuator saturation. Despite the importance of actuator saturation as a practical involvement in the control of autonomous vehicles, it has been considered less in control of AUVs. Therefore, the adaptive μ-modification control method is utilized in this paper for pitch channel autopilot of the REMUS AUV. The designed adaptive μ-modified controller has been applied to the nonlinear six degrees of freedom model of the vehicle. Coefficients of the model are assumed unknown to be coped with an adaptive controller. Performance of the designed controller is compared with that of a direct Model reference adaptive control (MRAC) in six degrees of freedom through simulations. Problems of the MRAC in the presence of input constraints are shown. Shortcomings of conventional adaptive methods in the presence of input constraints are studied. It is finally deduced that how the adaptive controller with μ-modification can perform suitable performance in the presence of the actuator saturation.