Doubly fed induction generator (DFIG) based wind turbines are sensitive to grid faults due to utilising small-scale rotor side converter (RSC). The application of crowbar protection to improve the fault ride-through (FRT) capability of the DFIG converts it to a squirrel cage induction generator, which makes it difficult to comply with grid codes. This study proposes an innovative DC-link controllable fault current limiter (C-FCL) based FRT scheme for the RSC to improve the FRT capability of the DFIG. The proposed scheme replaces the AC crowbar protection and eliminates its disadvantages. The C-FCL does not affect the normal operation of the DFIG. By means of the proposed scheme, rotor over-currents are successfully limited during balanced and unbalanced grid faults, even at zero grid voltage. Also, the C-FCL prevents rotor acceleration and high torque oscillations. In this study, an analysis of the proposed approach is presented in detail. The performance of the proposed scheme is compared with the conventional crowbar protection scheme through simulation studies carried out in power system computeraided design/electromagnetic transients, including dc software (PSCAD/EMTDC). Moreover, the main concept of the proposed approach is validated with an experimental setup and test results are presented.
Available for download on Wednesday, January 24, 2018