Research On Control Strategy Of Doubly Fed Wind Power Generation System Under Unbalanced Grid Voltage

In recent years, in order to actively deal with environmental and energy issues, domestic and international wind power industry rapidly develop, and its installed capacity continues to increase. Large-scale wind power penetration has brought the problems of stability of power grid and power dispatching difficulties and so on, the world's wind power access standards require wind farms have the ability to withstand power grid failure.Three-phase voltage asymmetry is a common problem that the wind power systems encountered. Doubly-fed wind turbines are currently the main models of wind farms, occupying a large proportion in the wind power industry. The control strategy of the bidirectional converter in the doubly-fed wind power system determines the operating characteristics of the wind turbine, but its design is based on the balance voltage of the grid. The original control strategy fail when the fault occurs, resulting in the doubly-fed wind power system separate from grid, which will lead to a large area of power outages, and even cause huge losses. Therefore, it is necessary to study how to improve the control strategy of doubly-fed wind power system to improve its grid connected operation capability in the grid failure.In this paper, DFIG is taked as the research object, whose mathematical model and the control strategy of back-to-back converter are established based on the working principle of DFIG and back-to-back converter. At the same time, the overall simulation model of the DFIG wind power system is built on the simulation platform.On the basis of above, the voltage asymmetry fault is analyzed, and the influence of the fault on the doubly fed power generation system rotor?stator and the DC bus is given. The fault voltage is reproduced in MATLAB/Simulink to analyze the variation law of electric quantity in the process of fault.Secondly, the fault voltage phase detection technology of the grid voltage fault is given,the stability of the DC bus voltage is not good because the negative sequence component exists in the grid voltage asymmetry fault, and the proportional resonance control strategy is used to instead of the traditional vector control, also the algorithm and block diagram is given, and the simulation and the result analysis have been done in the simulation software.Finally, for the voltage asymmetry fault in the grid, the rotor? stator voltage oscillation and overvoltage caused by the negative sequence component when using the vector control can not be well eliminated, the stator tracking rotor flux control strategy used in the rotor side converter,instead of the traditional vector control, the principle of control algorithm and the realization of the block diagram, and the simulation experiment and the result analysis are carried out in the simulation software.