Cooperative Control Strategy For Low Voltage Ride Through Of Doubly Fed Wind Farm

With the increasing penetration rate of wind power in the power grid,the position of wind power generation in the power grid is becoming more and more important.Double-Fed Induction Generation has become the wind turbine with the largest installed capacity in the world due to its low cost and excellent performance,and is the core part of wind power generation.In the wind power generation system,the capacity of Dual PWM converter in DFIG is small.Therefore,in case of power grid failure,DFIG will be greatly affected,and even endanger the safe and stable operation of doubly fed wind farm.Therefore,the research on the realization of low voltage ride through by DFIG is essential.Firstly,this essay analyzes the physical structure and operation principle of DFIG motor,analyzes the structure of each link and establishes a mathematical model;Then,based on the established mathematical model,the stability of doubly fed wind farm is analyzed,and it is concluded that the system has underdamping characteristics under vector control;According to this characteristic,a control strategy of virtual impedance control and switchable resistive type fault current limiter protection circuit working together is proposed,and an unloading circuit is added at the DC side to stabilize the DC bus voltage.The control strategy is applied to the doubly fed wind farm,which can accelerate its dynamic response and transient transition process.The low voltage ride through scheme proposed in this essay is simulated,and the results of 60% and 80% voltage drop are compared and analyzed.The results show that the collaborative control strategy proposed in this essay can significantly reduce the peak value of rotor current and control it below 2pu,the peak value of DC bus voltage is also significantly reduced,the torque fluctuation is small,the dynamic response speed is accelerated,and the low-voltage ride through capacity of doubly fed wind farm is greatly improved.In the development platform based on the PXI hardware of NI instruments,the overall design of the doubly-fed wind farm system is carried out,the dual PWM hardware circuit is designed,and the physical construction is carried out.The software program is designed on the basis of TMS320F28335.The physical quantities of the dual PWM objects built to verify their accuracy.