Research On Power Output Control Strategy Of Floating Wind Farm Considering Wake Effect

Compared with offshore bottom-fixed wind turbine,the additional six DOFs（degrees of freedom,DOFs）of FOWT（floating offshore wind turbine,FOWT）foundation make the unit components have larger displacements in all directions,and the motion range of rotor is the largest.The wake is an aera formed behind the rotor,and the characteristics of wake have a strong correlation with the rotor’s motion.The larger the displacement range of wind turbine,the more dispersed the wake expansion area,the faster the recovery of the wake loss speed,and the larger the influence range of the wake on the downstream units.The capacity of the offshore wind turbine is much larger than that of the onshore unit.In addition,the sea breeze is stable and the turbulence is low,and the speed loss in the wake area behind the wind turbine recovers slowly.Therefore,studying the wake characteristics of FOWTs and applying field-level control to floating wind farms can significantly improve the power output of wind farms throughout the life cycle,which is of great significance to increase the benefits of wind farms.At present,there are various types of floating platforms for FOWTs.Simulation research was carried out on wind turbines based on（Semi-submersible,Semi）,（Spar-buoy,Spar）type,（tension leg platform,TLP）type and Monopile type,and the tower base load,wake characteristics,etc.were analyzed.The single-unit power output and wind farm power output of the wind farm composed of these three types of floating and fixed units were simulated and calculated,and one type of FOWT was selected for this study according to the simulation results.Aiming at the control of floating offshore wind farms,this part was divided into the optimization of the wake model of FOWTs and the field-level control strategy.Firstly,simulating and calculating the wake characteristics of the selected floating wind turbines,mainly to calculate the change of wind speed in the wake region,and adding a coefficient to the original wake model to better describe the wake.Secondly,the three wake control methods of pitch,variable torque,yaw were analyzed,and the wake control method of the wind farm was selected.Finally,the objective function was iteratively solved by nonlinear programming,and the optimized data was obtained.In the simulation verification stage,the open-source tools of FAST.Farm and FLORIS were used to establish three types of wind farm layouts.According to the Wind Energy Manual and IEC standards,the turbulence density and other wind characteristics under the corresponding wind speed were calculated,and the appropriate sea conditions were selected.The medium and low wind speeds were simulated under the condition of field-level control or without control.The effectiveness of the control strategy proposed in this thesis was verified by analyzing the power output of a single unit and the entire wind farm.This thesis firstly compared and analyzed the component displacement range and load characteristics of different types of FOWTs,and selected a kind of floating wind turbine to build a wind farm to apply field-level control.Secondly,the original wake model was optimized to better adapt to the selected floating wind turbine.Finally,combined with the optimization algorithm,the model-based control strategy was used to simulate different external environments and wind farm layouts.