Grid-Forming IBRs Under Unbalanced Grid Conditions: Challenges, Solutions, and Prospects

The penetration of inverter-based resources (IBRs) into the grid is experiencing significant growth. Their control behavior during unbalanced grid conditions can impact system stability and protection. This paper evaluates the performance of prevalent grid-forming control-based IBRs (GFM-IBRs) under unbalanced grid conditions and proposes novel insights in a novel framework. First, we investigate the potential impacts of grid-forming control-based IBRs (GFM-IBRs) on system dynamics, protection, and fault ride-through (FRT) capability under unbalanced grid conditions based on extensive literature review and through EMT simulations in benchmark systems with IBRs. To discover these impacts and accommodate unbalanced grid conditions, we implement a generic control structure for full converter-based GFM-IBRs under FRT mode, then perform a comparative analysis of existing solutions that include sequence decomposition methods, positive sequence current-limiting methods, negative sequence controls, and current coordination methods, to identify their capabilities and limitations through literature review and EMT simulations in a large-scale power system. Finally, key challenges and solutions are discussed, highlighting prospects for future research.