Composite disturbance observer-based sliding mode control strategies for unmanned surface vehicles with unmatched...

Unmatched disturbances pose significant challenges to the control performance of unmanned surface vehicles (USVs), necessitating effective mitigation control strategies. This study proposes composite disturbance observer-based sliding mode control (SMC) strategies to address the trajectory tracking control problem of USVs under the influence of unmatched and matched disturbances, and input saturation. First, a composite disturbance observer is designed to estimate and compensate for the effects of both unmatched and matched disturbances. Subsequently, an SMC strategy is proposed to eliminate input discrepancies and ensure system state convergence within a designated region. Moreover, to mitigate the reliance on prior knowledge of the upper bounds of lumped disturbances, an improved SMC strategy is further proposed that incorporates a positive semi-definite barrier (PSDB) function. This strategy enhances the steady-state performance of the system and prevents excessive estimation of control gains. Finally, numerical simulations validate the effectiveness of the proposed control strategies.