Control of a vectorial propulsion underwater vehicle considering thruster hydrodynamics constraints and actuator saturation

Intervention-class autonomous underwater vehicles (AUVs) have to execute complex tasks such as underwater inspection and manipulating objects which demand high manoeuvrability along with good stability. Due to these contrasting capabilities, often the vehicle control activity demands high actuator outputs with almost zero time response. This condition leads to actuator saturation and limits the vehicle response to the control inputs. Another factor to be considered is the thrusters hydrodynamic constraints during propulsion which results in a highly nonlinear and coupled equations of motions. This forms the basic motivation to design a suitable nonlinear control methodology by considering the empirical data based thrust modelling, drag effects of the propulsion, and interaction effects of the external appendages and the hull of the vehicle. The capability of the proposed control strategy is evaluated by implementing a trajectory tracking problem. The simulation results prove the capability of the proposed control strategy to execute complex tasks in the presence of actuator saturation and hydrodynamic constraints.