AC fault on the inverter side of a hybrid multi-infeed DC transmission system will cause a drop in DC voltage and an increase in DC current. In severe cases

it may cause simultaneous commutation failure in multiple transmission lines. In order to provide voltage support to the receiving-end AC system by the MMC four-quadrant operation capability

based on the analysis of the LCC continuous commutation failure mechanism and the inverter side AC fault characteristics

an MMC transient voltage regulation control strategy based on fast reactive power-voltage droop control is designed; moreover

according to the different AC voltage sag degree

the selection method of its reactive power reference value is designed. When the AC bus voltage drop is small

the difference before and after the common coupling bus voltage drop is used to determine the MMC reactive power reference value. When the AC bus voltage drop is large

by establishing the relationship between the LCC DC current and the MMC reactive power output

a method of calculating the DC current limit based on the commutation voltage-time area theory to suppress the subsequent commutation failure of the LCC is proposed

and thus the reference value of the reactive power of the MMC outer loop is determined. Finally

the effectiveness of the proposed control strategy is verified by the simulation and comparative analyses of the communication faults of different severity.