Control of a Twin-Turbine Submerged Floating System in turbulent flow

Control of a Twin-Turbine Submerged Floating System (TTSFS) with Model Predictive Control (MPC) is discussed in this paper. The TTSFS has been developed to harvest Ocean Current Energy, and it has twin turbines and a weather-vaning ability by using a single-point mooring system. The TTSFS is perturbed and the output power fluctuates, due to turbulence in the flow. The aim of this study is to show the possibility to mitigate motions of the TTSFS and fluctuations of the output power simultaneously in turbulent flow, using blade pitch control and torque control of the generator. The control simulation is performed using a motion simulator which can simulate nonlinear 6 DoF motions of the TTSFS coupled with rotating twin-turbines and a single-point mooring system. Based on the simulation results, it is concluded that motion control is necessary to prevent large asymmetric motion which may affect the integrity of the mooring system. Also, MPC has the ability to mitigate motions of the TTSFS and the fluctuation of the output power simultaneously. However, there are tradeoffs among the variance of the motions, the variance of the angular velocity or the torque and the average of the output power.