Study On Protection Of Doubly-fed Induction Generator For Low Voltage Ride-through

Nowadays, rapid development in wind generator fields boosts the wind powerindustry. Doubly-fed induction generator (DFIG) has a lot of advantages in operationespecially in the decoupling control of active and reactive power. So, it has been themain generator used in new-built wind farms. If a DFIG does not have the ability oflow voltage ride through (LVRT), it will be tripped in low voltage fault time. And,when capacity of a wind farm is large, tripping of numerous DFIG will cause severeimpact to power grid. So study on LVRT of DFIG is very important. Crowbar is aneffective technique to improve the ability of DFIG’s LVRT, and parameteroptimization of its protection circuit is critical aspects in the study. In this thesis, itsoptimal control strategy and parameter optimization is deeply studied and discussed:1) A practical method to optimally select resistance of crowbar circuit is given.An index to evaluate the response of DFIG after some faults is firstly introduced.Then, relationship of the index value and the value of resistance is deeply studied inorder to derive the optimal resistance value. Simulations results reveal that thegivenmethod is simple, fast and useful.2) A method to optimally design control strategy of the chopper circuit andoptimally select bypass capacitance of the crowbar circuit is presented. The formerone is used to make the DC voltage more stable, and the later one is helpful to reducethe recovery cycle of fault current and voltage. Influence of these two components onthe evaluation index is deeply studied so as to determine their optimal values.Effectiveness and correctness of the given method is validated through numericalsimulations.3) Based on the platform of MATLAB/SIMULINK, a DFIG simulation model isbuilt, which is used in various simulations in the studies...