The Blade Pitch Control For The Floating Offshore Wind Turbines Bearing The Coupling Of Air-hydrodynamic Loads

Due to environmental pollution and energy crisis,and with the maturity of wind power technology,more and more countries have begun to promote wind farms to the wind-enriched ocean.China has a vast territory and a long coastline.The offshore wind energy resources are particularly rich and have a strong resource base.However,China’s offshore wind power technology is still in the ascendant,and offshore wind power is still limited to fixed wind farms in shallow sea.For the wind resources in deep sea whose quality is better and more stable,they are beyond the reach of the wind.Floating wind turbines proposed by various offshore wind power countries have become an effective way to solve this problem.The working condition and structural difference between the floating turbine and the fixed turbine make the floating turbine have the characteristics of floating body movement.The turbine system generates large fatigue load and aggravates the fluctuation of output power,which is not conducive to the safe operation and service life of the turbine.Based on this,the thesis aims to stabilize the output power of the floating turbine,alleviate the unbalanced load of the turbine system,and suppress the shaking of the foundation.This thesis studied from three aspects:the air-hydrodynamic modeling of the floating turbine,the dynamic response under the action of air-water coupling,and the pitch control technology based on unbalanced load.The main contents and structure are as follows:(1)The floating turbine is a highly nonlinear and strongly coupled system.Its dynamic motion is the aerodynamic load of wind load and the coupled response of hydrodynamic loads such as waves,currents and mooring loads.Based on considering the turbulence of wind,the shear effect and the tower shadow effect,the aerodynamic load model of the wind turbine is established by the theory of leaf momentum in this thesis.Then the wave and ocean current load model is established by using the Morsion-Equation.Finally,the system load model is established by linearization of the mooring system using the catenary theory,completing the establishment of the hydrodynamic load model.(2)Based on the established aerodynamic model and hydrodynamic model,the NERL-5MW wind turbine is taken as the research object,and 0C3-hywind is the supporting base.The Newtonou-Lafa method is used to establish the air-water power coupled model of the floating wind turbine.The FAST software is used to calculate and analyze the dynamic response of floating wind turbines under marine conditions,and to study its motion characteristics.The research shows that the dynamic response of the floating turbine in the air-hydrodynamic coupling is actually the combination of wind load and wave load;in the three degrees of freedom of surge,pitch and yaw,the wind and wave are closely coupled.The influence of the motion response amplitude in the system is large.(3)Considering the surge andpitch motions that have a great influence on the aerodynamic performance of the turbine,establish a mathematical model of the linear drive of the floating turbine wind wheel-transmission chain system-pitch controller-pitch actuator,and propose an individtual pitch control method of the floating turbine based on for RBF neural networks.The joint simulation under FAST and Matlab/Simulink shows that the pitch control method based on RBFNN can effectively compensate the wind and wave disturbance existing in the operation of the floating turbine,and can effectively realize the stable output power of the floating wind turbine.To some extent,the pitching motion of the turbine is suppressed,and the floating foundation pitching load is reduced.