An Algorithm for Effective Mitigation of Commutation Failure in High-Voltage Direct-Current Systems

High-voltage direct-current (HVDC) systems are being widely employed in various applications owing to their advantages, such as bulk power transmission, long-distance transmission, and power-flow control. However, HVDC systems suffer from commutation failure, a major drawback that leads to increased device stress, interruptions in transmitted power, and problems related to protection relay setting, in turn, resulting in system instability during operation. Therefore, many studies have investigated the mitigation of commutation failure by considering its underlying factors, that is, ac voltage reduction, dc current increment, and crossing point shifts of phase voltage. However, these approaches are limited in that they are unable to mitigate intermittent commutation failure in a transient state. This study proposes an improved algorithm that mitigates commutation failure by considering the results of previous studies as well as the control characteristics of HVDC systems. The proposed algorithm is tested in various scenarios, and the test results verify its feasibility.