| With the increasing large scale wind farms connected with grid, the problems in grid-connected wind farms are becoming more and more obvious. Some events of large-scale wind farms tripping had a worse impact on the stability of grid, make the relevant theory research, simulation and analytical in actual systems extremely urgent. A control strategy, which uses energy storage systems, is proposed to improve the voltage ride through capability and frequency stability respectively.The research in this subject mainly includes the following three aspects:(1) Firstly, the modeling and control strategy of DFIG-based wind power generator have been researched. The control objectives, like maximum power tracking, decoupling control of active and reactive power, have been accomplished by the use of vector control strategy. Made a high level of economy and practicality.(2) A coordinate control strategy, which uses super capacitor (SC)-based dynamic voltage restorer (DVR), is proposed to improve the voltage ride through of doubly-fed induction generators (DFIG). The voltage level of DFIG stator is fully compensated by SC-based DVR during grid faults. The active power of DFIG is decreased by the coordinate control to minimize the power rating of DVR. Zero voltage ride through, low voltage ride through and high voltage ride through during symmetrical and asymmetrical grid faults are simulated respectively. The validity of the proposed coordinate control strategy is verified by the simulation results.(3) Finally, a coordinate control strategy, which uses energy storage system, DFIG wind power generators as well as conventional synchronous generators, is proposed to improve the frequency dynamic stability in grid-connected wind farms. On the one hand, the fluctuation of frequency is suppressed and on the other hand, DFIG wind power generators can quickly revert to the initial maximum power operation status, which can participate in the next system frequency control. |
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