Nonlinear Lyapounov based control of an underwater vehicle in presence of uncertainties and obstacles

In this paper a strong robust nonlinear controller is proposed for an underwater vehicle based on Lyapunov theory which is able to bypass the local and moving obstacles using potential field approach. Underwater vehicles are nowadays widely applicable for performing both of inspectional and operational tasks under the surface of oceans. Considering the fact that in these environments additional external forces such as drag force of the fluid flow and many other disturbances can affect the performance of the robot, providing the stability and controlling the system in a robust way is extremely desirable. On the other hand, bypassing the local obstacles that are inevitable under the surface of oceans is another challenge that needs to be studied. In this paper a strong robust controller is designed and implemented on the nonlinear dynamic model of the underwater robot based on Lyapunov method which is also equipped by obstacle avoidance feature. As a result, not only the stability of the system is guaranteed and the robustness of the robot is provided against the external fluid forces and other exerted disturbances, but also the trajectory can be improved in order to bypass the stationary and moving obstacles. Model of the robot is first extracted. Afterwards the proposed Lyapunov based controller is designed and implemented on the robot. Obstacle avoidance algorithm is then designed using analytic approach of potential field method in order to bypass the local obstacles. The correctness of the robot modeling and the efficiency of the designed controller is verified by the aid of some analytic and comparative simulation scenarios in MATLAB. It is shown that by the aid of the presented model of underwater robot and its related proposed control, the system can successfully perform any mission with a high accuracy and robustness even in the presence of obstacles.