Short-Circuit Modeling of DFIGs With Uninterrupted Control

Doubly fed induction generators (DFIGs) exhibit very different short-circuit behavior than synchronous generators, and the conventional voltage-behind-reactance model typically used for short-circuit calculations is not appropriate for generators of this type. A new short-circuit model is proposed in this paper for DFIGs under balanced faults and uninterrupted control of the rotor-side converter (RSC) and grid-side converter (GSC). The proposed positive-sequence short-circuit model represents the RSC and GSC as controlled current sources within the conventional induction machine steady-state equivalent circuit. Short-circuit calculations using the proposed positive-sequence model of the DFIG are compared with transient simulations of a megawatt-scale DFIG under a three-phase fault. Additionally, calculations using the proposed model are compared with experimental short-circuit test results on a 6.8 kVA, 230 V DFIG testbed. From the experimental tests, it is found that mutual-flux saturation in the DFIG significantly affects the short-circuit behavior, and these effects are discussed in detail in this paper.