Adaptive Sliding Mode Path Tracking Control for an Underactuated Unmanned Surface Vehicle Based on a Disturbance Observer

ABSTRACT To address the issues of low path‐tracking accuracy and poor robustness for underactuated unmanned surface vehicles under complex marine environments with model parameter uncertainties and unknown time‐varying disturbances (wind, waves, and currents), a novel adaptive sliding‐mode composite control strategy is proposed. The core of this strategy is the design of a disturbance observer (DOB) to estimate the lumped disturbances caused by the environment and unmodeled dynamics online, which is then used as a feedforward term for active compensation. On this basis, an adaptive sliding‐mode controller is designed for feedback stabilisation. Specifically, an adaptive law is responsible for identifying and compensating for the internal hydrodynamic parameter uncertainties online, while the sliding‐mode control term ensures the system's robustness and fast convergence in the presence of residual errors and rapidly changing disturbances. Through a series of numerical simulation studies, the proposed method is compared with a conventional PID controller. The results demonstrate that under the same harsh sea conditions, the proposed method can significantly improve path‐tracking accuracy, effectively suppress external disturbances, and ensure the smoothness of the control output, showing its great potential for practical applications.