| Recently, National-Energy-Commission releases a government document whichis named “Technical code for design of large grid-connected wind turbines”. Itrequires that when grid went wrong, the generator system must have some ability ofLow-Voltage-Ride-Through (LVRT).Firstly, this article will introduce the working principle of the Doubly-Fed-Induction-Generator (DFIG), and it has determined the mathematical model of theDFIG. Secondly, it will analysis of the adverse consequences what unstable workingbrings. Some detection methods are introduced for voltage sag. A new method calledSoft-Phased-Locked-Loop (SPLL) is used now. A notch filter is used to separate thepositive and negative sequences. In order to achieve the function of LVRT, a activecrowbar is designed. And this article analysises and chooses the IGBT which is usedin the crowbar circuit. Then energy storage device is added into the system for theleisure time.Finally, based on PSCAD/EMTDC platform, this article simulates a DFIGsystem. The LVRT scheme is simulated when voltage sag occurs. The result showsthat the method is truly successful. Finally, the experiment proves that the DFIGsystem has some ability of LVRT with the help of the new crowbar and the auxiliarycircuit. |
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