When the power grid fails, the rotor side of doubly-fed induction generator (DFIG) will have overcurrent and the DC side of frequency converter will have overvoltage. In addition, the large fluctuation of stator and rotor current will cause the electromagnetic torque of doubly-fed wind turbine to oscillate violently, which will produce huge torque and shear stress on the mechanical system of wind turbine. In order to study the influence of crowbar resistance on the impact electromagnetic torque of doubly-fed wind turbine when the power grid fails, a transient mathematical model of doubly-fed wind turbine system based on stator orientation vector control strategy is established.
On this basis, considering the adverse effects of overvoltage, overcurrent constraint and impact torque on gearbox and fan, the influence of crowbar resistance on DFIG impact torque is studied. Under the most serious three-phase symmetrical short-circuit fault and two-phase asymmetrical short-circuit fault, the crowbar resistances of three kinds of DFIGs with the same capacity but different parameters are simulated and compared, and the peak characteristic curves of generator electromagnetic parameters under low voltage ride-through under crowbar protection are obtained. The results show that the impact torque of doubly-fed wind turbine is closely related to the crowbar resistance value when the power grid fails, and the crowbar resistance value has great influence on the impact torque of generators with different parameters.
On this basis, considering the adverse effects of overvoltage, overcurrent constraint and impact torque on gearbox and fan, the influence of crowbar resistance on impact torque of doubly-fed wind turbine is studied. In the case of the most serious faults of three-phase balanced short circuit and two-phase asymmetric short circuit, three groups of input crowbar resistors of doubly-fed generators with the same capacity but different parameters are simulated and compared, and the peak characteristic curve of generator electromagnetic parameters during low voltage passing under crowbar protection of doubly-fed generators is obtained. The results show that the impact torque of doubly-fed wind turbine is closely related to the crowbar resistance value when the power grid fails, and the crowbar resistance value has a relatively strong influence on the impact torque of generators with different parameters.
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