Enhanced differential protection for weak-infeed lines emanating from grid-following DFIG based wind plants during balanced faults

The current differential protection (CDP) functions as the primary protection for the lines emanating from wind plants. This paper reveals that the limited current contribution capability of grid-following (GFL) controlled doubly-fed induction generators (DFIG) is just one of the challenges that CDP may encounter; due to the isolation from the external grid during balanced faults, the fault current output of GFL-DFIG could conflict with the realistic power balance constraints when complying with modern grid code (GC) requirements. Such contradictions may manifest as a frequency deviation pattern detected by the differential relay, with the resulting errors in magnitude and phase angle extraction potentially compromising sensitivity or causing CDP failure. To enhance the performance of CDP in the presence of weak-infeed lines connecting GFL-DFIG-based wind plants, this paper devises a new CDP scheme based on the ρ plane. The novel differential criterion utilizes the current magnitude ratio to optimize the restraint boundary with concave characteristics and employs the composite dynamic time warping (DTW) distance metric to indirectly calculate the current phase difference. In comparison to traditional CDP methods, the proposed approach does not rely on synchronized data and maintains high adaptability to the unique fault current signature of GFL-DFIG. Detailed simulation results under various fault scenarios, including instances of CT saturation and high-frequency harmonic interference, validate the effectiveness of the proposed CDP scheme.