Grid-Forming Control for Reactive Power Sharing in Bipolar MMC–HVDC Systems Under Asymmetric Grid Conditions

HVDC systems operating under asymmetric grid conditions. When unequal electrical impedances exist between the converter points of common coupling (PCCs) and the common point of interconnection (POI), conventional PCC-oriented GFM control can lead to inconsistent voltage formation at the POI and unintended reactive power circulation between converter poles.

To address this issue, an Impedance-Compensated Grid-Forming Control (IC-GFM) strategy is proposed. By compensating the PCC–POI impedance within the voltage reference generation, the proposed approach aligns the effective voltage formation of each converter toward a common POI condition rather than regulating local PCC voltages, while preserving fully decentralized GFM operation.

The proposed control is validated using a 2GW bipolar MMC–HVDC system with asymmetric

PCC–POI impedances. Simulation results demonstrate that IC-GFM effectively improves reactive power sharing and maintains well-aligned transient and steady-state behavior between converter poles, even under differing electrical conditions at the PCCs.

These results confirm that reference-level impedance compensation provides a practical and scalable solution for robust GFM operation of bipolar HVDC systems under asymmetric grid conditions.