Synthesis of a finite-time convergence controller for trajectory tracking of unmanned underwater vehicles
Narcizo Nuci, Néstor Alejandro
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Unmanned underwater vehicles have gained importance since they can perform tasks in underwater environments such as exploration and construction. Proper control of the vehicle trajectory is fundamental for successfully complete a task. When disturbances are frequent and the dynamics of the vehicle change, fast response of the control scheme is required and the classical controllers do not adapt to overcome these conditions. As the main contribution of this work, we propose the synthesis and implementation of a control scheme with finite-time convergence applied to the trajectory tracking including a time variable gain in the sliding surface of a 2nd Order Sliding Mode Control. In the first part, the parameterized trajectory considered five degrees of freedom: x,y,z, \phi, and \psi. In a second part, an emulation of a simultaneous scheme between two vehicles is proposed, taking advantage of the finite-time convergence of the proposed controller. The dynamic parameterization of the vehicle is based on the BlueROV2 vehicle by BlueRobotics, which counts with four horizontal and vectored thrusters, and two vertical thrusters. A finite-time second-order sliding-mode controller will be synthesized by applying a variable gain on the sliding surface. This gain will be parametrized by a Time Base Generator. The controller was tested to determine its performance, accuracy, and prompt response for trajectory tracking in space and was compared against classical controllers: a Proportional-Integral-Derivative Controller, a Feedback Linearization controller, and a Lyapunov function-based controller. In the second part, the controller was compared with two state-of-the-art controllers, that also count with finite-time convergence. The proposed control schemes will be evaluated in a simulator constructed in a Matlab/ Simulink environment with the actual parameters of the underwater vehicle, and where the parameters of the RMS values of the tracking error and the RMS values of the control signals are analyzed to evaluate the performance of the controllers. The results of this work demonstrated that it is possible to synthesize the 2nd Order Sliding Mode Controller with finite-time convergence and apply it in the trajectory tracking of underwater vehicles, in trajectories that involved the five degrees of freedom, and even in the presence of marine currents. The results of this thesis are expected to be implemented in future work related to trajectory tracking and collaborative tasks with underwater vehicles.