Transient Stability Analysis of Grid-Forming Converters with Current Limiting Considering Asymmetrical Grid Faults

TL;DR

This paper investigates the transient stability of grid-forming converters during asymmetrical faults, deriving a new P-δ curve that accounts for negative-sequence effects, validated through simulations and experiments.

Contribution

It introduces a novel P-δ curve for GFM-VSCs with current limiting under asymmetrical faults, explicitly considering negative-sequence influences for improved stability analysis.

Findings

Derived the P-δ curve considering negative-sequence effects.

Validated the theoretical model with simulation and experimental results.

Enhanced understanding of GFM-VSC stability under asymmetrical faults.

Abstract

Under asymmetrical faults, analyzing the transient stability of grid-forming voltage-source converters (GFM-VSCs) becomes essential because their behavior fundamentally differs from that under symmetrical faults. When current limiting is activated under asymmetrical faults, the point-of-common-coupling voltage of a GFM-VSC contains both positive- and negative-sequence components, and the interaction between these components generates a non-negligible negative-sequence-driven active power. However, the transient stability of GFM-VSCs under asymmetrical faults has not been sufficiently investigated, and the influence of negative-sequence-driven active power remains unclear. Accordingly, this letter derives the P-{\delta} curve of a GFM-VSC with an elliptical current limiter under asymmetrical faults by explicitly accounting for negative-sequence effects. This enables a more accurate transient stability assessment when extending conventional symmetrical-fault analyses to asymmetrical conditions. The theoretical analysis is validated by the agreement between the derived P-{\delta} curve and both simulation and experimental results.