Heading Control of Autonomous Underwater Vehicle

Abstract

An autonomous underwater vehicle(AUV),is an untethered, self-propelled, unmanned, underwater vehicle able of carrying out assigned task with little or no human supervision.Because its versatile nature AUV finds application in defence organizations, sea floor mapping, underwater surveys, oil and gas industries, marine industries research, etc.
Controlling of an AUV is a challenging task. Autonomous underwater vehicle is an under actuated system. External disturbance like ocean waves and hydrodynamic effects influencethe dynamics of AUV. To perform the underwater application AUV need self-governing guidance and control system. The main objective of this thesis is heading control of AUV. For heading control initially standard Model Predictive Control (MPC) is used. But this controlling technique failed to compensate disturbance affecting the AUV. Hence for the compensation of disturbance acting on AUV Active Disturbance Rejection Controller (ADRC) is used.
Heading control also recognized as ‘course keeping’. The control law is designed such that it forces AUV to reach and maintain the fixed desired direction. Rudder orientation act as the control input that help the AUV to maintain the constant heading angle. But there are physical limitations on the movement of rudder.High yaw rate can induce roll and sway motion, which can cause seasickness. Hence it is necessary to put constraints on rudder orientation and yaw rate while navigation of AUV in seaways.
Model Predictive Control is a control scheme, which inserts optimization within feedback so that the system can deal with the constraints present in the input and states of the system.
This is the main reason of using MPC in industrial applications. The MPC is very beneficial to handle control and input constraints. But with disturbance in the system there is constraints violation while heading control of AUV.
The Nomoto model is commonly used one for the heading control design of an AUV. 1 DOF Nomoto model with constant disturbance and sinusoidal disturbance is considered. Simulation has been performed for standard MPC.
Later Active disturbance rejection control (ADRC) is used for the compensation of disturbance. This control strategy actively estimates the total disturbance (internal and external disturbances)and also reduce it. In the simulation it can be seen that in the presence of disturbance the AUV can trace the desired heading angle using ADRC controller.