A Transient Interaction Mechanism Analysis Method for the Grid-Forming Voltage Support Device Integrated into LCC-HVDC System

The sending end of the line-commutated converter based high-voltage direct current (LCC-HVDC) system will undergo a "low-then-high" transient voltage fluctuation when faults occur at the receiving end. Consequently, reactive power compensation devices are often employed to enhance the transient voltage stability of LCC-HVDC sending-end systems. However, there is insufficient analysis regarding the transient voltage support mechanisms for these reactive power compensation devices integrated into LCC-HVDC systems. To address this problem, this paper develops an equivalent model for a grid-forming voltage support device (GVSD) integrated into LCC-HVDC system, illustrating its reactive power compensation process during the "low-then-high" transient process. On this basis, an analysis method based on the short-circuit ratio (SCR) is proposed to clarify the transient voltage support mechanism for GVSD. Finally, the accuracy of the proposed method is confirmed through simulations.