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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.

Vehicle-Fixed-Frame Adaptive Controller and Intrinsic Nonlinear PID Controller for Attitude Stabilization of a Complex-Shaped Underwater Vehicle