Abstract
In this study we present attitude stabilization using a vehicle-fixed-frame adaptive controller and an intrinsic nonlinear PID controller for a low-speed Autonomous Underwater Vehicle (AUV), of complex shape. Controlling an AUV poses a huge challenge because of the non-linearity, time variance and unpredictable external disturbance, as well as because its dynamics and hydrodynamic parameters are difficult to identify due to its geometry. First, a vehicle-fixed-frame adaptive controller is implemented to stabilize the attitudes given. The stability of this desired state-dependent, regressor, matrix-based controller is verified using Lyapunov’s direct approach. Second, an intrinsic nonlinear PID controller is implemented based on the attitude error represented as rotation matrices, to stabilize the attitudes given. This controller requires only an approximate estimate of the inertia tensor of the device. Both the controllers adopt quaternions to indicate the attitude errors to avoid representation of the singularities that occur when the Euler angle description of the orientation is used. Finally, the results imply that the intrinsic nonlinear PID controller has more stability and shorter settling time than does the vehicle-fixed-frame adaptive controller.
Highlights
Over the last two decades, Autonomous Underwater Vehicles (AUVs) have come in a wide variety of types and shapes and exerted a great influence on underwater applications
This study considers the problems of attitude stabilization for a complex-shaped AUV, in the presence of external disturbances
The simulation results demonstrate the comparison between the attitude stabilization of the vehicle-fixed-frame adaptive controller and the intrinsic nonlinear PID controller to be effective and robust to external disturbances
Summary
Over the last two decades, Autonomous Underwater Vehicles (AUVs) have come in a wide variety of types and shapes and exerted a great influence on underwater applications. In the literature reports are available on techniques that are recommended for following the attitudes and trajectory tracking methods in the AUVs. in the course of designing suitable controllers, the main difficulties encountered include the uncertainty of the hydrodynamic parameters, such as the non-linear hydrodynamic effects, variations in the parameters and disturbances due to the ocean currents, as well as the nonlinear dynamics of the AUV. This study presents a vehicle-fixed-frame adaptive controller and an intrinsic nonlinear PID controller for a complex-shaped AUV to stabilize the attitudes given. The AUV kinematics and dynamics are clearly depicted, indicating the highly non-linear and coupled terms, which poses a challenge for the mathematical model
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