• Proposed an advanced current limiting strategy for grid-forming inverters to meet IEEE 2800 during unbalanced faults. • Developed adaptive power reference control for synchronization enhancement. • Implemented K-factor-based current injection and a current scaling limiter for full converter utilization. • Demonstrated flexibility and effectiveness of the grid-forming decoupled-sequence control across various fault conditions. Grid-forming converters are increasingly deployed to connect renewable energy sources to the grid, but their control behavior during unbalanced grid faults can affect system stability and protection. To comply with the IEEE 2800 standard under such conditions, it is essential to regulate both positive and negative sequence currents. This paper proposes an adaptive current limiting control based on a decoupled-sequence control structure for grid-forming converters, allowing independent regulation of sequence components and flexible integration of various power synchronization loops and current limiters. Building on this structure, the adaptive control incorporates adaptive power reference-based synchronization control, advanced current reference generation, and an improved current limiter to ensure compliance with IEEE 2800 requirements, including reactive current injection and full utilization of converter current capacity during unbalanced faults. Case studies demonstrate that the proposed strategy enables grid-forming converters to deliver optimal current injection, satisfy grid code requirements, and accurately emulate the negative sequence behavior of synchronous generators under unbalanced fault conditions, marking a significant advancement in the modeling and control of grid-forming converters for grid integration.
Chen et al. (Sun,) studied this question.