Grid-Forming STATCOM for Commutation Failure Mitigation in LCC-HVDC System

Conventional high-voltage direct current (HVDC) transmission systems are widely employed in large-capacity, long-distance power delivery scenarios. However, due to the reliance on thyristor-based line-commutated converter (LCC) lacking self-turn-off capability, commutation failures are likely to occur when the alternating current system is weak or subjected to disturbances. The static synchronous compensator (STATCOM), a shunt-connected reactive power compensation device, can inject or absorb reactive power to support the LCC-HVDC inverter side, thereby mitigating commutation failures. Nevertheless, traditional grid-following STATCOMs exhibit stability limitations under weak grid conditions, as their performance is inherently tied to grid strength. With the rapid integration of renewable energy sources, modern power systems increasingly exhibit "dual-high" characteristics, heightening instability risks for conventional STATCOM. In this study, grid-forming control technology is applied to STATCOM devices. Grid-forming control enhances stability in weak grids by emulating the rotor dynamics of synchronous generators to autonomously regulate voltage and frequency. A simulation platform integrating grid-forming STATCOM and LCC-HVDC systems is established in PSCAD/EMTDC. Case studies demonstrate the superior capability of grid-forming STATCOMs in suppressing commutation failures under weak grid conditions compared to conventional grid-following counterparts.