Grid Forming Control of Delta-H Bridge Module Under Unbalanced Conditions

Static synchronous compensators (STATCOMs) are essential in power systems for improving power quality by providing voltage regulation, reactive power support, harmonic reduction, and flicker mitigation. Two widely used topologies for STATCOMs are the star H-bridge module (S-HBM) and the delta H-bridge module (D-HBM). The S-HBM usually requires a higher DC bus voltage due to the need for zero-sequence voltage injection, while the D-HBM operates without this requirement, making it a more voltage-efficient alternative. However, the D-HBM commonly uses a phase-locked loop (PLL) for grid angle detection, which is sensitive to grid disturbances and can degrade system performance. To address these limitations, this paper introduces a grid-forming (GFM) control strategy for the D-HBM. GFM control enhances the system's ability to balance capacitor voltages, maintain dynamic stability, and deliver fast response times. A detailed analysis of these challenges is provided, demonstrating the improved performance of GFM-controlled D-HBM under various operating conditions. Experimental results highlight the robustness of the proposed GFM method, showing stable operation in both balanced and unbalanced grid scenarios. These findings confirm the GFM-based D-HBM as a reliable and efficient solution for STATCOM applications in real-world power systems.