Nonlinear Control for an Active-passive Hybrid Compensation System

Equipment handling and offshore installations in harsh sea conditions can be a difficult task, and vessel motion always handicaps the operation of marine equipment. Hence, heave compensation system is used to decouple load motion from ship motion when lifting, lowering or holding a load, and reduce variation in cable tension. This paper provides a comprehensive model of an active-passive hybrid heave compensation system(APHHC), with servo valve, friction and nonlinear structure taken into consideration. Based on the mathematic model, back-stepping sliding mode control is applied to keep a constant displacement for an underwater load. The MATLAB simulation results prove the effectiveness of the proposed controller. The mathematic model and the nonlinear control mothed in this paper can be a guide to real systems.