Controllable DC-link bridge-type FCL for low voltage ride-through enhancement of converter interfaced DG systems

Recently penetration level of converter-interfaced distributed generation (DG) systems has been increased in utility and will be more so in the future. To avoid grid instability, converter-interfaced DG should have low voltage ride through (LVRT) capability considering grid codes. An efficient scheme is proposed to enhance the LVRT capability of converter-interfaced DGs. The proposed LVRT technique employs a single phase controllable DC-link bridge type fault current limiter (CD-BFCL), which is placed in DC side of the converter. During normal condition, the CD-BFCL does not affect overall operation of converter-interfaced DG; whereas, during all AC faults including balanced, unbalanced, and transient repeated network faults, converter output AC currents are limited to a desired level. In this way, the converter-interfaced DG is capable to ride through faults even at the zero grid voltage during the AC grid faults. Analytics and modes of operation of the CD-BFCL are presented during switching intervals to demonstrate the efficiency of the proposed approach in limitation of converter over-current. The operation of the proposed method is proved through simulation studies in PSCAD/EMTDC. Also, a laboratory prototype is developed to validate the possibility of practical implementation of the CD-BFCL.