For the MMC-HVDC system connected to a passive network

the active power balance will be broken and the DC voltage will fall rapidly when the AC fault occurs at the sending end

which also will threaten the safe operation of the converter station. Firstly

the passive network load characteristics and the variation mechanism of the electrical quantity of the converter station under AC fault are analyzed in this paper. Then

based on the conventional control of inverter station connected to a passive network

an additional fault ride-through control strategy is proposed to produce d-axis voltage correction instruction according to DC voltage variation. The core idea of the control strategy is as follows: when the active power of sending end loses rapidly

the active power output of the inverter station is reduced through modifying the command value

so as to maintain the active power balance of the converter station at both ends and restrain the DC voltage sag. Finally

an MMC-HVDC system connected to a passive network is simulated on the PSCAD/EMTDC. The results show that the proposed additional control can decrease the DC voltage sag

reduce the active power fluctuation at the sending end during recovery after fault cleaning

and improve the AC fault ride-through capability of the system.