Funnel anti-pitching control of trimaran using extended state observer under wave disturbances

To mitigate the significant amplitude variations in heave and pitch motions of trimaran under strong wave disturbances in class 4 sea state, this study proposes a novel funnel-based anti-pitching control strategy employing a composite error-based extended state observer (ESO). The control method ensures rapid convergence of heave and pitch motions within the predefined performance funnel function. By integrating wave disturbances, nonlinear convolution terms and coupled heave-pitch motion terms as the lumped disturbance, the vertical motion model of trimaran is decoupled into the decoupled heave and pitch models. A novel composite error-based ESO is designed, incorporating both the observation and feedback errors, to enhance disturbance estimation accuracy. The estimated value of the lumped disturbance is then compensated via feedforward control. Leveraging the rapid convergence characteristic within the performance funnel function, a simplified funnel controller is developed using the backstepping method. The composite control strategy combining ESO compensation and funnel control significantly improves the anti-pitching performance of trimaran. Numerical simulations demonstrate a 49% reduction in both heave displacement and pitch angle under the proposed control strategy.