Study on a Wave Energy Converter With Tension Leg Mooring Under Optimal Control

Abstract

A safety assessment for wave energy converters (WECs) in model scale is necessary before a demonstration test. WECs have various control conditions such as a maintenance and power generation mode etc. Although the safety assessment is required to carry out while considering the control conditions, the motion and load characteristics of the moored WEC to which applies various control conditions remains unclear. This study investigated the motion and load characteristics of the WEC including a mooring system when each control conditions was used. In experiments, the motion and load characteristics of the WEC without control were revealed. In the simulation, the motion and load characteristics were compared between two control methods which are the resistive loading control (RLC) and the approximate complex-conjugate control with considering the copper loss (ACL). The control methods have little effects on the surging, pitching and bending moment of the WEC. Mooring tension increased with increasing wave period when the RLC was used. When the ACL was applied, mooring tension reached the peak value near the natural period and decreased with increasing the wave period. The difference in the trends leads to that the control method maximizing mooring tension is not necessarily the same in each wave period. The select of the operating condition based on the wave period is required when the mooring tension of the WEC is assessed in the model-scale test stage.