Research On Power And Load Coordinated Control Strategy For Large Wind Turbine

At present,the research on wind turbine control strategy at home and abroad mainly focuses on power and load control.The power control includes the maximum power tracking below rated wind speed and the power stability control above rated wind speed.The load control refers to the load optimization in the full wind speed range.However,the current research on load control is mainly in the stage above rated wind speed.In fact,the wind speed fluctuates more frequently when the wind speed is below the rated.The gust,turbulence and wind shear effect not only affect the maximum power point tracking of the turbine,but also exacerbate the blade flap-wise bending and edge-wise displacement,which furthermore influences the blade fatigue load and is harmful to the long-term safety and the reliable operation of wind turbine.The thesis studied the power and load control below rated wind speed to achieve the maximum power tracking,suppress the load and realize the coordinating control of power and load.The main research contents are as follows:(1)The basic composition of permanent magnet direct drive wind power generation system was introduced,and the fundamental theory of wind energy conversion was expounded.The load type was determined by the load analysis during the operation of the wind turbine and based on the blade element momentum.A method for calculating the aerodynamic load of the blade was given.According to the operation principle of each part of the wind turbine,the mathematical models of wind speed,wind wheel,transmission chain and permanent magnet synchronous generator were established,which laid a foundation for the research and simulation analysis of control strategy.(2)Two common methods of vector control of permanent magnet synchronous generator were studied,and a double closed loop controller was designed.Based on that,the optimal tip speed ratio power tracking control strategy was studied.Aiming at the problem that the control process relies on the real-time measurement of wind speed,an improved sensorless-based optimal tip speed ratio control method was presented.Combining the parameters of 3MW permanent magnet direct-drive wind turbine,the optimal tip speed ratio method before and after improvement were simulated and analyzed.The results prove the effectiveness of the improved optimal tip speed ratio method in power tracking,but find the hysteresis in impact load suppression.(3)In view of the limitation of optimal tip speed ratio control and its improved method for impact load suppression when the wind speed changes abruptly.Combining the advanced lidar wind measurement technology,the thesis proposed a pre-pitch control strategy based on the wind speed prediction and constructed its controller.The controller controls the pitch time base on the predicted wind speed sequence and outputs the pitch angles.The method achieves the suppression of the impact load while ensuring the maximum power tracking.The simulation results demonstrate the feasibility and effectiveness of the control strategy for the coordinating control of power and load.