Enhanced constant extinction angle control for subsequent commutation failure in LCC-HVDC

To mitigate subsequent commutation failure (SCF) in line-commutated converter-based high-voltage direct current transmission systems, the response and limitations of the control system are analysed. The results reveal that due to the prolonged negative deviation of the extinction angle during recovery, the integral output of the proportional–integral controller in constant extinction angle (CEA) significantly reduces the advanced firing angle order, even below normal operating angle. This directly leads to a delayed transition between control strategies and diminishes the effectiveness of CEA. Furthermore, the influence of fault severity, fault type, and AC system strength on SCF is examined. Based on these findings, an enhanced CEA control method to suppress SCF is proposed. By setting an expected firing angle and adaptively adjusting the integral parameter, the control strategy switching moment can be advanced, improving the CEA's control margin and enhancing capability. Moreover, introducing a notch filter reduces firing angle fluctuations and strengthens CEA's ability to suppress SCF. Finally, the theoretical analysis and the effectiveness of the proposed optimization method are validated.