Robust Control of Autonomous Underwater Vehicles Using Delta-Sigma-Based 1-bit Controllers

Autonomous underwater vehicles (AUVs) are robots capable of operating underwater without the need for human operators. Nonetheless, there is the essential requirement of remote operation capability in case of exceptional situations, such as the encounter of unforeseen obstacles or malfunctions. The corresponding robust controller design is a challenging task, especially due to limited communication bandwidth to the land based control system as well as the exposure to disturbances like water currents. The present study, therefore, proposes a Delta-Sigma-based 1-bit PID controller for such AUVs, which consumes less communication resources and is robust to various disturbances arising in the underwater environment. The proposed controller is designed using the Takagi-Sugeno (T-S) fuzzy model of the nonlinear AUV systems. A comparative performance investigation of this controller is carried out with an output feedback controller as reference design, which is based on the same T-S fuzzy model. The stability conditions of both controllers are established. Obtained simulation results indicate that in case of extreme disturbances and limited bandwidth, the reference controller could not stabilise the AUV system. In contrast, the proposed Delta-Sigma-based 1-bit PID controller performed well under all conditions, while using less hardware and communication resources compared to the reference design.