| Wind energy,as a renewable and clean energy source,occupies an important position in the field of new energy development in China.Wind power generation has an increasing impact on the power system,and optimising its control technology and studying new control strategies are always important topics.This paper takes reducing the abandoned wind rate of China’s wind turbines and increasing the system power output as the entry point to control the wind turbines in the operating state below the rated wind speed in order to maintain the purpose of maximum power output.Based on the fact that fractional-order calculus has been widely used in various engineering fields in recent years and has achieved good control results,this paper introduces fractional-order calculus theory into the control of wind power generation system at low wind speed and maximum power output stage.The main work of this paper is as follows:(1)The direct-drive permanent magnet synchronous wind power generation system,which is widely used in wind power generation,is selected to connect the wind turbine to the grid with a two-level dual PWM full-power converter,and its mechanism model is built in MATLAB/Simulink to keep the system in grid-connected stable operation with a constant power factor of 1.A good platform is established for the application of fractional-order control strategy.(2)To address the problem that the exact wind speed value is difficult to measure and the optimal speed given value is difficult to determine because the maximum power of the system is constantly changing,the MPPT control strategy based on the perturbation search method of OPC curve is proposed to obtain the optimal speed given value,which has achieved certain results,but there are problems of long search time and small oscillations after stabilization.(3)To address the above problems,a support vector machine MPPT composite control strategy based on fractional-order particle swarm optimization is proposed.In order to obtain a high-precision wind speed estimation model,a time-factor-based fractional-order particle swarm optimization(TFFV-PSO)algorithm is used to rectify the parameters of the wind speed estimation model,and the perturbation step size is changed in real time according to the predicted wind speed value to improve the shortcomings of the above method.This enables the system to quickly search for the optimal speed given in the case of unknown wind speed,and enhances its immunity to disturbances.(4)After determining the optimal speed,the controller of the speed loop of the machine side vector control system is studied and improved.The fuzzy fractional-order PI controller is designed,the fuzzy language variables of the integration order are changed,the fuzzy rules are reformulated and the control effects of the integer-order PI controller,the fractional-order PI controller and the fuzzy fractional-order PI controller are compared.It is proved that the fuzzy fractional-order PI controller can significantly improve the control performance of the wind power generation system at the stage of maximum power output at low wind speed,with faster response speed and stronger robustness,and optimize the problem that the integer-order PI controller and fractional-order PI controller have poor control effect under the drastic change of measured wind speed,which has certain reference significance and application value. |
