Rapid identification method of commutation failure risk areas in HC-HVDC systems under single-phase faults

• The DC control system's effect is considered while computing the generalized node voltage interaction asymmetry factor. This method is beneficial and can quantify the voltage interaction between two grid nodes in any system control mode, and is highly applicable. • Based on the conduction sequence of the commutator valve and the line voltage, an expression for the inverter-side extinction angle containing the voltage variation is derived as a commutation failure criterion under a single-phase grounded short-circuit fault. • By considering the transient behavior of the DC current that continues during the fault process, an improved method for calculating the voltage variation of the critical commutation failure is proposed, improving the calculation's accuracy. • The asymmetric factor of critical generalized node voltage interaction was proposed. A rapid and accurate approach for identifying the commutation failure risk areas under single-phase ground short-circuit faults in HC-HVDC systems was proposed, which is critical for power grid safety and stability. The hybrid cascaded high voltage direct current (HC-HVDC) systems combine MMC and LCC features. However, single-phase ground faults on the AC lines of the receiving end power grid can easily cause LCC commutation failure on the inverter side. To accurately determine the areas of commutation failure risk in HC-HVDC systems, this study first regards all AC buses and fault points as generalized nodes. It proposes a generalized node voltage interaction asymmetry factor, considering DC control. Then, the converter valve’s conduction sequence and the effect of the reverse line voltage were analyzed, and an expression for the inverter-side extinction angle, which includes voltage variation, was proposed as the commutation failure criterion for single-phase faults. Secondly, considering the DC dynamic characteristics during the fault process, calculate the variation of the critical commutation failure voltage and the critical index value under single-phase faults. By combining the distribution characteristics of the index values at different fault locations, a rapid identification method for commutation failure risk areas under single-phase faults is ultimately obtained. Finally, a complete electromagnetic transient model of the hybrid cascade DC system was established using the PSCAD/EMTDC platform. Simulation verification indicates that the accuracy of this method is approximately 35% higher than that of traditional methods, demonstrating the efficacy of the calculation and identification methods described in this study and providing a theoretical basis for enhancing system monitoring and protection strategies.