Research And Optimization On Fatigue Load Characteristics For Large-scale Offshore Wind Turbine Drivetrain

Drivetrain is the key component for the energy transmission of offshore wind turbines.Fatigue damage is one of the main reasons for the failure of drivetrain components.It is the man method to reduce the life cycle cost of offshore wind turbines that optimzing the fatigue load of the drivetrain,which is of great significance to ensure the safety and reliability of wind turbine operation and the economic benefits of wind farms.Under the support of the National Key R&D Program of China"Optimal Design and Batch Manufacturing Process and Inspection Technology of Key Components of Large Offshore Wind Turbine Drive Chain"(2018YFB1501304),based on the 5MW offshore wind turbine,a 2 degree of freedom PID pitch controller is designed to mitigate the load of divetrain.The main research contents are as follows:(1)In order to analyze the mechanism of the torsional vibration of the drivetrain,a torsional vibration dynamic model is established about speed-up offshore wind turbine based on the lumped Mass Method,which proves that the torsional vibration of drivetrain can be suppressed by optimizing pitch controller.(2)With the goal of cooperative optimization about the output characteristics of the wind turbine and the fatigue load of the drivetrain,a pitch control strategy based on the 2 degree of freedom gain scheduling PID is designed.And the performance of the controller is verified by GH Bladed.(3)According to the IEC standard,fatigue load conditions of offshore wind turbine is designed,which can be utilized for the analysis of drivetrain fatigue load characteristics under the coupling of wind and waves.To obtain the load time history of the drivetrain,the fatigue loads are calculated under the traditional gain scheduling PID and 2 degree of freedom gain scheduling PID pitch control strategy,respectively.(4)The power spectral density of the drivetrain torque is calculated based on the Fourier transform according to the time series load.The equivalent fatigue load of the drivetrain is calculated based on the rain flow counting method.As a consequence,the performance of the pitch controller is analysed from the frequency domain and time domain individually.It is shown that the fatigue load of the drivetrain is optimized by the 2 degree of freedom gain scheduling PID pitch controller.