Disturbance rejection control Strategy of Stewart-gangway hybrid system for active wave compensation

For offshore wind maintenance, wave compensation enhances both operational efficiency and personnel safety. Stewart-gangway platform (SGP) offers an effective approach for active motion compensation. Current motion planning methods underutilize the nine degrees of freedom of SGP, risking overlap or reverse compensation. Furthermore, traditional control methods lack the robustness to counteract complex maritime disturbances, severely degrading trajectory tracking accuracy and ultimately causing the platform’s active compensation to fail. This study proposes a composite disturbance rejection control architecture for the SGP. A multi-task planning strategy is improved by using the null space method, and a new controller consisting of the sliding mode controller (SMC) and an extended state observer (ESO) is designed. Meanwhile, a new reaching law is designed to suppress the chattering of the SMC. Stability of this strategy is proved by the lyapunov theory. Compared to the baseline computed torque control with ESO in simulation, the proposed strategy yields an average reduction of 82.7% in MAE and 82.8% in RMSE for end-tracking, exhibiting better performance in both motion compensation accuracy and disturbance rejection capability. Notably, the residual disturbance errors that exceed the estimation capability of ESO are effectively compensated. Moreover, the SMC with new reaching law significantly reduces the output chattering.