An ADRC-based triple-loop control strategy of ship-mounted Stewart platform for six-DOF wave compensation

Abstract

The ship-mounted Stewart platform can accurately compensate the 6-degree-of-freedom (6-DOF) wave motion of offshore vessels to facilitate the transfer of personnel and cargoes. They usually equip high-power electric or hydraulic actuators with high nonlinearity, large inertia and parameter perturbation. The lower platform is exposed to random wave motion and the upper platform is subjected to time-varying load interference. In addition, there are strong coupled inertia between the limbs of Stewart platform. These problems make it difficult for the ship-mounted Stewart platform to achieve accurate 6-DOF wave compensation. In this paper, a triple-loop control strategy based on active disturbance rejection control (ADRC) is proposed for the electric-driven ship-mounted Stewart platform, where the internal model controller (IMC) in the current-loop is designed to realize rapid dynamic adaptation of torque, the sliding model controller (SMC) in the velocity-loop is designed to adjust the velocity steadily, and the ADRC in the position-loop is designed to estimate and compensate the total position disturbance. The results show that the proposed control strategy has excellent performance in the power reduction, decoupling control and disturbance resistance. Under the random wave excitation in 4-level sea state, the proposed control strategy can improve compensation deviation by about 4.4 times and compensation stationarity by 4 times compared with PI controller.