Current Estimation and Path Following for an Autonomous Underwater Vehicle (AUV) by Using a High-gain Observer Based on an AUV Dynamic Model

A path following problem for autonomous underwater vehicles (AUVs) under a nonuniform current is presented in this paper. A dynamic model of an AUV in a nonuniform flow was adopted to develop a high-gain observer (HGO) for estimation of the three-dimensional current velocities along AUV trajectories. The HGO was chosen as a nonlinear estimation algorithm, and the observer gain was computed by solving a Linear Matrix Inequality (LMI) which represented the estimation error dynamics. The current velocities were determined by calculating the differences between the measured absolute velocities of the vehicle and the estimated relative velocities of the vehicle estimated by the observer. The estimation error means of the HGO using the LMI have smaller values than the state observer with a gain matrix determined by the pole-placement approach. For the path following study, the desired curved path was represented by using a Serret-Frenet frame which propagated along the curve. The path-following system includes a guidance law, an update law and a proportional and integral controller. Two cases of numerical simulations were conducted to verify the performance of the path following system combined with HGO for current compensation, and the results of both cases have shown that the AUV reached and converged to the desired path.