Attitude Control of Underwater Vehicle out of Water Based on Implicit Nonlinear Dynamic Inversion.

In explicit nonlinear dynamic inversion (NDI) control, a system is linearized accurately using nonlinear offset. However, because of the inversion errors in offset from the uncertainties of real models, the robustness of control system is hard to be guaranteed. Explicit NDI is found facing serious challenges when solving the motion issue of underwater vehicle exceeding water. Considering the severe change in hydrodynamic force and the strong impact of waves, its attitude control has become a research focus. Firstly, the control law of dynamic inversion in the form of implicit increments is derived and obtained, and the system is divided into a slow loop and a fast one using the idea of stepped construction on the base of affine motion model of underwater vehicle out of water. Then the feedback of state variation rate is introduced, the implicit control law independent of accurate models and with better robustness is designed based on these two time-scale separated loops. Finally, based on the implicit NDI control algorithm, the attitude of underwater vehicle in its out-of-water process is traced under the influence of waves and perturbation of hydrodynamic parameters and measurement noise, and the validity and rationality of the control law are verified. [ABSTRACT FROM AUTHOR]