This paper presents a cost-effective scheme to improve the fault ride through capability of wind turbines with doubly fed induction generators. As an alternative to using crowbar, the proposed scheme includes the stator side series-connected braking resistors, dc-link chopper and coordinated control strategy of the whole system. The proposed scheme enable the rotor converter always be connected to the system such that the DFIG will not lose controllability during fault and can almost immediately generate reactive power to support the grid after the beginning of the fault. The series-connected braking resistors can help the transient decay very fast and, at the same time, dissipate the energy of the wind turbine to reduce the rotor speed deviation during fault. Dynamic behavior of DFIG-based wind turbines during grid faults is discussed based on theoretical analysis and simulation results. It is shown that the proposed scheme can not only help the whole system ride through the fault but also reduce the stress on turbine mechanical systems.
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