The Application of the Digital Controlled Hydraulic Cylinders Group in Pendulum Wave Energy

Wave energy is one of the most important potential sustainable energy resources. To enhance the performance of the pendulum hydraulic wave energy converter (WEC) system in various wave conditions, this article proposes a digital controlled hydraulic cylinders group to replace the single traditional hydraulic cylinder in a hydraulic power take-off (PTO) system based on the concept of previous study. The cylinders group, whose structure is designed with high extendability, consists of several pairs of subsidiary cylinders. The extraction energy maximizing for pendulum WEC is theoretically analyzed in the frequency domain based on a linear wave assumption, which indicates demand for damping regulation. The proposed cylinders group is able to provide variable damping for the PTO system by changing its working area. So as to demonstrate the better performance of the proposed cylinders group compared with a single traditional hydraulic cylinder, a simulation in AMESim software and a fundamental semiphysical test have been carried out. Both results illustrated that the WEC was endowed with high performance by using cylinders group in various wave conditions. In addition, a transmission efficiency test indicated that the application of the cylinders group did not cause much more extra energy loss during the transmission process compared with the single traditional cylinder. The further study of cylinders group with more subsidiary cylinders and the control strategy remains to be conducted.