Side Effect of VSC-HVDC on Commutation Failure in LCC-HVDC Caused by Sending End AC Faults

This letter presents a new phenomenon that the integration of voltage source converter based high voltage direct current (VSC-HVDC) can increase the risk of commutation failure (CF) of line-commutated converter based HVDC (LCC-HVDC) caused by sending end AC faults, and reveals the underlying mechanism. It is found that VSC-HVDC accelerates the recovery of the active power of LCC-HVDC after fault clearance in a hybrid multi-infeed HVDC. This leads to a phase shift of the commutation voltage and high DC current in the LCC inverter, which is the inherent reason for the increased risk of CF under severe faults. And the DC impulse current is the direct reason for the increased risk of CF under moderate faults.