Study on the system design and control method of a semi-active heave compensation system

The heave compensation system is essential for the installation of subsea equipment. A new semi-active heave compensation system is designed and the control system is analysed, with the aim of solving heave movement problems during deep-water installation. The heave compensation is implemented with a pulley block system and actuated by a compound hydraulic cylinder. The control system can switch between passive compensation mode and semi-active compensation mode. The state-space equations of both modes are set up based on the mechanical and hydraulic system models of the compensation system. With the state-space equations, three control strategies are compared based on the classic Proportion Integration Differentiation (PID) control, and the limitations of PID control are also analysed. In order to avoid defects of the PID controller, the active disturbance rejection control (ADRC) technology is introduced, and a newly developed second-order ADRC controller is applied in the tension control strategy for heave compensation, which results in improved compensation effect.