Nonlinear optimal internal model control for AUVs under wave disturbances

Abstract

A nonlinear optimal internal model control (NOIMC) for autonomous underwater vehicles (AUVs) under wave disturbances is designed. Firstly, nonlinear model of AUVs in vertical plane is obtained, and an exosystem model of wave disturbance is generated based on Hirom approximate formula. Secondly, a disturbances compensator is constructed based on the internal model principle such that the AUVs system with wave disturbances is transformed into an augmented system. Then, a NOIMC law with a compensation term is designed by the maximum principle and the successive approximation approach, which can realize the optimal control when the system has none disturbances; While the wave disturbance exists, this obtained NOIMC law can reject the disturbance with zero steady-state error because of the existence of the internal model. Finally, the effectiveness and feasibility of the NOIMC law is demonstrated by a numerical example of the Remote Environmental Unit (REMUS) AUV.