Commutation failure immunity index(CFII) is an index that can effectively measure the effects of AC-DC system parameters and controller regulation to commutation failure.Using CIGRE benchmark model in PSCAD

based on CFII index

the influence mechanism of HVDC controller parameters

DC system parameters and AC system parameters on commutation failure is simulated comprehensively.Simulation results show that the increasing AC system strength at the inverter side or decreasing the short circuit impe-dance of the converter transformer can effectively improve CFII

and CFII will be increased only when the equivalent impedance angle increases to a certain degree.Increasing the flat wave inductance or decreasing the equivalent capacitance of the DC transmission line can significantly improve CFII.Increasing the gain of constant current controller at the rectifier side to a certain value increases CFII significantly.CFII is increased when increasing the constant extinction angle order.The results provide a theoretical reference for the study of commutation failure prediction and suppression methods.