Sliding Mode Controller for Positioning of an Underwater Vehicle Subject to Disturbances and Time Delays

Unmanned underwater vehicles are crucial for deep-sea exploration and inspection without imposing any danger to human life due to extreme environmental conditions. But, designing a robust controller that can cope with model uncertainties, external disturbances, and time delays for such vehicles is a challenge. This paper implements a sliding mode position control algorithm with a time-delay estimation term to a remotely operated underwater vehicle to deal with disturbances, such as waves, and time delays. The controller is implemented on an underwater vehicle (BlueRov) and compared with a proportional-integral-derivative (PID) controller in a wave tank with different disturbances and when there exist delays within the communication channel. The experimental results show that the proposed control method provides better performance than the conventional PID in the presence of extreme disturbances with less control efforts.

I. Introduction

Unmanned underwater vehicles (UUVs) are used for deep-sea exploration, oceanographic data collection, inspecting subsea structures (e.g., pipes, valves, cables within the energy and telecommunication industries), and for military purposes such as to discover and terminate underwater mines. Depending on the complexity and structure of the task, they can either be teleoperated from a ship where the remotely operated vehicle (ROV) continuously communicates with the surface vehicle via a tether/cable or have full autonomy where the autonomous underwater vehicle (AUV) operates without human intervention. The UUVs require a robust controller to accomplish operator commands or to autonomously follow trajectory waypoints under environmental disturbances such as water currents and waves or when there exist time delays within the communication channel [1], [2].