Adaptive robust control for an active heave compensation system

Active heave compensation systems are usually employed in offshore and deep-sea operations to reduce the adverse impact of unexpected vessel’s vertical motion on the response of underwater instruments. This paper presents a control strategy for an active heave compensation system consisting of an electro-hydraulic system driven by a double rod actuator, which is subjected to parametric uncertainties and unmeasured environmental disturbances. Adaptive observer and discontinuous projection type updating law with bounded adaption rate are presented firstly to estimate the uncertain system parameters. Then a similar estimation algorithm is designed by using a multiple delayed version of the system to enhance the performance of parameter observation. A reduced order observer is also introduced to estimate unknown wave disturbances. Using the obtained uncertainty information, the resulting control development and stability analysis are implemented based on the Lyapunov’s direct method and back-stepping technique. The proposed controller guarantees the heave compensation error convergent to a bounded neighborhood around the origin. Simulations illustrate the effectiveness of the proposed control system.