Grid Forming Control of Star Connected Cascaded H-Bridge STATCOM

In modern power systems, maintaining voltage sta-bility, enhancing power quality, and ensuring reactive power support are crucial, especially with the growing incorporation of renewable energy sources and distributed generation. Static syn-chronous compensators (STATCOMs) are crucial for mitigating these challenges. Using modular multilevel converters (MMCs) as STATCOMs enhances reactive power compensation and voltage regulation. Among various MMC-STATCOM topologies, the star connected cascaded H-bridge (SC-CHB) is favored because of its simpler architecture, lower voltage stress, fewer components and cost-effectiveness. Traditional SC-CHB STATCOMs oper-ate in grid-following (GFL) mode, which is inadequate under weak/unbalance grid or isolated operation due to reliance on grid for phase angle acquisition. Grid-forming (GFM) control, mimicking synchronous generators, provides autonomous volt-age and frequency regulation, crucial for grid stability with high renewable energy penetration. Implementing GFM control in MMC-based STATCOMs, particularly SC-CHB STATCOM, poses challenges such as voltage balance across the H-bridge modules (HBMs), stability during disturbances, and fast dynamic response. This paper explores GFM control implementation for SC-CHB STATCOM, addressing aforementioned challenges under different test case scenarios like lag/lead reactive power compensation, unbalance load etc. Finally, a hardware prototype of 370 V/± 5 kVAR, 7-level 3-phase SC-CHB STATCOM has been built to validate the proposed GFM control.