Adaptive Current Limit Control for Half-Bridge MMC-HVDC Single Pole-to-Ground Fault

Integrating renewable energy sources into a bipolar modular multilevel converter (MMC) via a common AC bus can lead to an increase in AC in-feed current during a single pole-to-ground (PTG) fault, resulting in bridge arm overcurrent and a blocking risk for the MMC. To address this problem, an adaptive current limiting control (ACLC) that accounts for the AC in-feed current boosting effect is proposed. First, a dynamic model of AC in-feed current rise in a faulty MMC is developed to analyze the mechanism of bridge arm current increase. The capacitor discharge between the bipolar MMCs is identified as the root cause of the bridge arm overcurrent. Then, the dynamic ACLC model is built for the bipolar MMC to reduce the AC in-feed current by differentially adjusting the number of inserted submodules in each MMC in the bipolar MMC. Finally, the proposed ACLC is validated through real-time simulation, showing a 43.66% reduction in peak bridge arm current to avoid the risk of MMC blocking and superior current-limiting performance compared to other methods.