Simplified failure analysis method for DFIG-based wind farm outgoing transmission line

When a non-bolted-three-phase-fault occurs in the outgoing transmission line from a DFIG-based wind farm with low-voltage-ride-through (LVRT) capability, the wind power side bus voltage and short-circuit current may have inconsistent main frequencies. This paper is devoted to exploring the reason theoretically. Based on the fundamental of induction generators, a simplified three-order dynamic model of the induction generator is established in the d-q rotating coordinate system. In a period after a short circuit failure, the DFIG-based wind generator with LVRT capability can be equivalent as a transient potential behind a transient reactance and the frequency of the transient potential varies with the machine´s rotor speed before the failure. Based on that equivalent circuit model of DFIG, a simplified failure analysis method can be used for the DFIG-based wind farm outgoing transmission line, thus explaining the reason for the frequency inconsistency from the circuit-theory perspective. The method is verified by a simulation system established on the PSCAD/EMTDC platform.