Research On Frequency Regulation Control Strategy For Wind Farm Cluster Considering Fatigue Load

Wind energy is one of the rapidly growing renewable energy sources.At present,it has become the third largest energy source in the world.As the penetration of wind power increases,the impact of grid integration of wind power with volatility and uncertainty on grid security becomes more significant.The pressure of the grid can be relieved if large-scale wind farm clusters participate in grid frequency regulation.And the grid frequency stability will be enhanced.However,the power reference is frequently changed by the frequency regulation controller to adapt to changes in the grid frequency when the wind power participates in frequency regulation.The frequent action of the pitch angle and the torque is caused by this change,resulting in an increase in the fatigue loads of wind turbines.The life of the wind turbine will be affected.Therefore,it is necessary to study the frequency regulation control strategy of wind farm cluster considering fatigue load.The research focuses on the control method of the three layers of wind turbine-farm-cluster.Because the wind turbine will run in derating mode after participating in frequency regulation.Therefore,in the wind turbine level study,the NREL-5WM wind turbine model of the National Renewable Energy Laboratory is improved.Then the control strategy of increasing tip speed ratio,which can reduce the fatigue load of the unit,is focused on.A method to reduce fatigue load by reducing torque fluctuations is proposed.It provides a theoretical basis for the subsequent researches.At the wind farm level,an active power dispatch method based on wind turbine fatigue load sensitivity is proposed to reduce fatigue loads.First,the state space equation of the wind turbine is established,and the analytical equation of the fatigue load sensitivity is re-derived.Therefore,the accuracy of the fatigue load sensitivity calculation is improved.Then the total fatigue load of all wind turbines in the wind farm is taken as the goal of optimization.The tracking power reference value is the constraint.The active power distribution model is established.A quadratic programming optimization algorithm is used to calculate the power reference of each wind turbine.Finally,the controller is tested for different operating conditions.The advantages of the proposed method are verified by comparing the cumulative rain cycle and equivalent damage load.At the wind power cluster level,a system identification adaptive optimal PID control method that considers wind turbine fatigue load and power system frequency response is proposed.First,the fatigue load on the low-speed shaft torque and tower bending moment is taken into consideration and the wind turbine model is improved.The improved wind turbine model is added to the dual-region load frequency control model including thermal power and hydropower.Then,the system identification adaptive proportional integral differential controller is designed to consider the system frequency response and wind turbine fatigue load.Based on the multi-objective functions,the optimization algorithm is used to optimize the PID parameters.Finally,the controller's effectiveness is verified.