Research On Pitch Control Strategy Of Large Offshore Floating Wind Turbine System

Compared with the onshore power generation,offshore wind power generation has been vigorously developed in recent years due to the advantages of not taking land resources,abundant wind resources and close to power load center.However,with the wind power resources development of the tidal zone and coastal areas intensity gradually saturated,and the voice of environmental protecton of the coastal areas growing,the offshore wind power generation from the intertidal zone and offshore areas to the deep sea is an inevitable trend in the future.Floating wind turbines,as a wind turbine mounted on a floating platform,provide a viable solution for wind power from offshore to distant sea.However,for floating wind turbines,the external loads and system models are more complex than land and offshore wind turbines.Therefore,there is an urgent need for advanced control methods to ensure that the floating wind turbine can maintain a steady power output under complex external loads and system models uncertainty,while also reduce the influences of the pitch control to the floating platform load.In addition,the probability of the actuators and the sensors failture of floating wind turbine will rise accordingly in this condition,seriously affecting the reliability of wind turbines and power stable output.In view of this,the paper will focus on the generation power smooth output of deep-sea floating wind turbines in the fault-free and fault conditions.The main research work completed includes:(1)Establishment of floating wind turbine structure model.Based on the basic dynamics theory of floating wind turbine,the mathematical model of its main part is established.According to the aerodynamic performance characteristics of wind turbine,a generalized nonlinear mathematical model of wind energy conversion system is established.According to the dynamic performance characteristics of the floating wind turbine structure,the structural dynamic model of the limited degree of freedom of the floating wind turbine is established.A second-order mathematical model,actuator failure model and sensor failure model of the pitch system are established for the wind turbine pitch system.(2)Design of pitch control strategy for floating wind turbine in fault-free condition.In this paper,a pitch control strategy for offshore floating wind turbines based on active disturbance rejection control is designed for the complex loads and model uncertainties caused by winds,waves and currents in floating wind turbines.The control goal of the controller is to avoid increasing the platform pitch movement caused by the power control on the premise of guaranteeing the stability of power output.Using the high simulation nonlinear wind turbine model(FAST)provided by the American Renewable Energy Laboratory(NREL)and the simulation of the control strategy with Matlab / Simulink.The results show that the proposed method has better power control effect compared with the gain control PI control strategy.(3)Active fault tolerant pitch control strategy for floating wind turbine under pitch system fault.In this paper,an active fault-tolerant control strategy based on multiple fault reconstruction is designed to solve the problem of actuator and sensor faults simultaneously in floating wind turbine pitch system.The control strategy can ensure the steady output of the wind turbine power to a certain extent when the pitch actuator and the sensor fail simultaneously,and thus improve the reliability of the wind turbine to a certain extent.The simulation results show that the proposed active fault-tolerant control strategy has some fault-tolerant ability for single fault and multiple faults of pitch system.