NMPC-PID control of secondary regulated active heave compensation system for offshore crane

In this paper, an offshore crane driven by a secondary controlled unit (SCU) which offers advantages in terms of high dynamic behavior and energy efficiency is investigated. To counteract the negative impact of the support vessel's heave motion on the station-keeping and trajectory tracking performance of heavy payload, an adaptive robust control scheme for the secondary regulated active heave compensation (AHC) system is proposed based on the combination of a nonlinear model predictive control (NMPC) strategy, a conventional proportional-integral derivative (PID) control scheme and a vessel heave motion prediction algorithm. The motivation of utilizing the PID-based control structure is given by the excellent resistance against irregular external disturbances and robust capability to eliminate the uncertainties, with real-time tuning gains provided by the NMPC synthesized with the autoregressive integrated moving average (ARIMA) model to ensure optimal evolution that satisfies state and input constraints while accounting for model nonlinearities. Comparative simulation studies in the practical Simulink-based mechanical-electrical-hydraulic research system demonstrate the superior tracking and heave compensation performance, strong robustness, constraint satisfaction, and energy efficiency of the proposal.