Back-stepping control of underactuated AUV's depth based on nonlinear disturbance observer

In order to track the desired depth of underactuated autonomous underwater vehicle (AUV), a back-stepping controller based on nonlinear disturbance observer(NDO) is proposed. Firstly, the dynamics model of AUV in the vertical plane is simplified to be more practical for the construction of controller; secondly, the back-stepping controller of AUV's depth is designed along with NDO. Based on the Lyapunov's principle, the overall stability of the whole system is proved to be guaranteed. In the end, the results of the simulation indicate that the designed controller shows strong robustness to the external disturbance, and achieves satisfactory control performance.