Three-dimensional trajectory tracking of a hybrid autonomous underwater vehicle in the presence of underwater current

In this work, a six degrees-of-freedom (DOF) nonlinear kinematic and dynamic model of a Hybrid Autonomous Underwater Vehicle (H-AUV) is derived for the two modes of locomotion, propelled and gliding modes. A comprehensive linearization algorithm is developed to include both modes of locomotion. Starting with a three-dimensional time-parameterized curve of position history, Frenet-Serret frames are used to specify the unknown nominal states, which in turn are used to obtain the nominal inputs. A linear time-variant (LTV) state-space model is obtained, and a linear quadratic regulator (LQR) is designed and applied to the nonlinear model. The performance of the devised controller is assessed via a metric that computes the error between the actual and the desired position. Simulation results show that the LQR provides accurate tracking performance, even in the presence of underwater currents with bounded flow velocity. Moreover, the controller autonomously switches modes between propulsion and gliding to ensure minimal trajectory tracking error and energy consumption.