Commutation Failures Caused by DC Line Faults in Double-Circuit LCC-HVDC Transmission Lines

The mechanism of commutation failure (CF) caused by dc line faults in double-circuit LCC-HVDC transmission lines is investigated in this paper. Fault analysis for double-circuit HVDC transmission lines is given to present the current increase at inverter side. The commutation process is also demonstrated to further investigate the CF problems. Then, the transient performance of conventional control system at inverter side is discussed in case of current fluctuation. It indicates that conventional control system is incapable of resisting CF by steep current increase. Therefore, an improved control scheme is developed based on the current prediction to mitigate CF by transient current increase. Simulation results show the proposed control method has the ability to reduce the CF risk effectively in most cases.