Comparative Research of Nonlinear Decoupled Tracking Controller Design for an Open-Frame AUV

This study presents the design and implementation of two different nonlinear controllers for trajectory tracking control of an open-frame observer type Autonomous Underwater Vehicle (AUV). The AUV's dynamics are modeled using the Newton-Euler formalism, and the state-space representation is obtained. The controller comparison consists of two nonlinear controllers for horizontal motion control in planar coordinates(x,y): Backstepping Control (BS) and Sliding Mode Control (SMC), and a Linear Quadratic Regulator (LQR) for controlling the depth and rotational dynamics. Both controller structures are designed to ensure stability using the Lyapunov stability criteria for trajectory tracking while LQR guarantees stability by placing eigenvalues on the left half plane for depth and rotational dynamics. The system states are decoupled to facilitate control design, and Simulink models are developed to validate the controllers' performance in the presence of sinusoidal disturbance. The results show that both BS and SMC provide robust and accurate tracking performance under sinusoidal disturbances, while LQR exhibits good performance in the remaining coordinates.