Impact of Synchronous Condenser on Commutation Failure of LCC-UHVDC Transmission System Hierarchically Connected to Weak AC Grid

This paper investigates the impact of Synchronous condenser (SC) on transient performance of LCC-UHVDC system hierarchically connected to weak AC grid which may exhibits consecutive commutation failures (CF) and longer fault recovery time under different fault conditions. The SC as a dynamic reactive power compensator is connected to AC busbar of LCC-UHVDC system in order to supply reactive power during various transient conditions. The LCC-UHVDC hierarchical connection mode along with SC is developed in PSCAD/EMTDC. The effect of SC on operating characteristics like CF and fault recovery performance of LCC-UHVDC system hierarchically connected to weak AC grid is analyzed under single and three phase to ground fault. The results indicate that SC increases AC system strength, which can effectively regulate AC bus bar voltage, mitigate the occurrence of commutation failure at inverter side and considerably improve the fault recovery time of LCC-UHVDC system under different fault conditions.