Asymmetrical Fault Ride Through as Ancillary Service by Constant Power Loads in Grid-Connected Wind Farm

The introduction of distributed generation (DG) into low voltage (LV) systems demands that the generation system remain grid connected during voltage sags to ensure the operational stability. The DG consisting of fixed speed squirrel cage induction generator (SCIG)-based wind turbines is unable to provide reactive power control and needs a dedicated compensating device. Under asymmetrical grid faults the negative sequence flux circulation in the airgap introduces the torque oscillations that lead to the reduction of lifetime of the generation system. This paper proposes the use of distributed constant power loads (CPLs) for asymmetrical fault ride through (FRT) instead of using a centralized STATCOM. It has also been observed that the compensation of negative sequence voltage improves the performance of SCIG by eliminating the torque ripples. The compensation of positive sequence voltage avoids a possible voltage collapse at the LV distribution level and improves the reliability and stability of the wind farm. Centralized compensation of the asymmetrical grid fault by a STATCOM is compared with the distributed compensation by CPLs. The results suggest that each individual CPL injects lower current for maximum FRT enhancement compared to a dedicated STATCOM.