Improved Commutation Failure Prevention Control for Inter-Phase Short-Circuit Faults

To enhance the resistance to commutation failures of high-voltage direct current (HVDC) transmission systems under interphase short-circuit faults, an improved commutation failure prevention (CFPREV) control strategy is developed and validated. Initially, the adaptability of conventional CFPREV under interphase short-circuit faults is analyzed, and the time-varying mismatch between its three-phase criterion and the actual fault-phase voltage drop magnitude is quantified, thereby revealing the limitations of existing CFPREV control in handling interphase faults. Then, an innovative phase-by-phase real-time voltage drop calculation algorithm is proposed, which requires no integration and can be realized using only two adjacent sampling points. The calculated phase voltage indices remain stable during normal operation and respond rapidly after faults, ensuring the fast activation of advance firing control. On this basis, a real-time prediction algorithm for commutation voltage zero-crossing offset is further developed, and an improved CFPREV control strategy is designed. Subsequently, two real-time algorithms are proposed: a per-phase voltage drop magnitude calculation algorithm and a commuta-tion voltage zero-crossing shift prediction algorithm. Based on these, an improved control strategy is designed. Finally, simulation results using the PSCAD V46/EMTDC platform con-firm that the proposed strategy significantly improves commutation failure mitigation under interphase short-circuit faults compared to conventional CFPREV.