Linear active disturbance rejection control with linear quadratic regulator for Stewart platform in active wave compensation system

• The inverse kinematic model of the branch chain is established. • The controller is designed for the position loop of the electric cylinder actuator. • The controller realizes decoupling, anti-disturbance and easy parameter tuning. • The proportional-derivative gain is substituted with a linear quadratic regulator. Offshore operations are vulnerable to the vessel motions caused by waves in harsh sea conditions. To compensate for the wave-included motions of the vessel, the shipborne Stewart platform with a gangway mechanism offers an effective means to enhance operator safety and extend the window period for offshore activities. The gangway endures off-center heavy loads and low-frequency vibrations, while the shipborne Stewart platform faces time-varying ship motions caused by waves. In addition, there is a strong motion coupling between the limbs of the Stewart platform. These challenges pose a formidable task in attaining precise control accuracy for wave compensation. In this study, a linear active disturbance rejection control with a linear quadratic regulator is proposed for the shipborne Stewart platform. The original proportional-derivative gain is substituted with a linear quadratic regulator (LQR), thereby effectively addressing the previous challenge of channel parameter tuning. Additionally, a linear extended state observer is devised to enhance system robustness by estimating and counteracting overall disturbance. The proposed controller is designed based on joint-space and its stability is verified using the Lyapunov theory. Simulation results validate that the proposed controller demonstrates superior performance in terms of compensation accuracy, anti-disturbance capability, and decoupling effect compared to the PI and LQR controllers.