Hierarchical Adaptive Control for Path-Following and Pitch Stabilization of a Vector Propulsion Amphibious Vehicle

Wind, wave, and current disturbances degrade the attitude stability of under-actuated amphibious vehicles and jeopardise their safety. To enhance path-following accuracy as well as pitch stability, this study proposes an adaptive control strategy that combines backstepping with line-of-sight (LOS) guidance for a vector propulsion amphibious vehicle (VPAV). Firstly, a six-degree-of-freedom (6DOF) nonlinear model coupled with environmental models are established. Subsequently, hierarchical adaptive path-following and pitch controllers are devised through the backstepping approach, while a daisy-chain thrust allocation mechanism is integrated to reconcile the competing requirements of path-following accuracy and pitch stability. Additionally, an adaptive saturation compensation method is introduced to mitigate actuator saturation. The stability of the proposed method is theoretically proven. Comparative simulations demonstrate superior speed, tracking precision, and disturbance rejection compared with benchmark methods.