Coordination Control Strategy Of DFIG-based Wind Powerintegrated System For Power Transient Voltage Stability

With the rapid development of wind power generation technology, the wind power penetration rate is getting higher and higher, and this will inevitably cause a lot of adverse effects on the safe a nd stable operation of the power system. Due to the defects of wind energy, such as random and intermittent, the voltage stability of wind power integrated system has been becoming hotspot issues. The structures of the doubly-fed wind turbine make it sensi tive to the fluctuation and faults of the grid side. So, it has important theoretical and practical significance to study the control strategy of transient voltage stability of doubly-fed wind power integrated system. In this thesis, the transient instabil ity mechanism, control strategy and reactive power compensation are studied.Firstly, three factors are analyzed that influence on the transient voltage stability of doubly-fed induction generator: pitch angle, rotor over current protection, grid side converter. The wind speed model, synchronous generator model, pitch control model and the doubly-fed wind turbine dynamic model are established. By studying the influence of the power grid fault on the stator and rotor voltage and the generation of the DC bus, the mechanism of transient instability of DFIG is analyzed.Secondly, aiming at the problem of rotor over current of doubly-fed induction generator in grid fault, the low voltage ride through capability of DFIG based on Crowbar is studied; Influence of selecting resistance and switching time of Crowbar on the control effect has been analyzed by simulation. Then, for the problem of increasing the reactive power of the system caused by the input of Crowbar, the contribution of DVR based on the improved vol tage sag detection algorithm and the compensation control method to the low voltage ride through capability of doubly-fed wind generator is studied. According to the advantages and disadvantages of the two strategies, this thesis proposes a coordinated con trol strategy based on Crowbar and DVR, this strategy not only can effectively restrain the rotor current, but also can compensate the voltage sag faults, improving the transient stability of the system.Finally, from the point of view of the wind farm clu ster group, a hierarchical coordination control strategy of wind farm group is proposed: the reactive power demand of the whole system is calculated by the wind farm collection station, and the reactive power assignment is allocated to each wind farm; Cons idering the voltage stability index, the reactive power margin of the DFIG, STATCOM and DVR of the wind farm, a multi objective function model is established, the reactive tasks were assigned to the DFIG, STATCOM and DVR through the glowworm swarm optimization algorithm. The control strategy is verified by the simulation and analysis of the control strategy in the wind power fluctuation and power grid fault in the MATLAB/Simulink.