In hybrid-HVDC transmission system

voltage source converter is used in inverter station

by this thecommutation failure would be avoided

it would be used widely for multi-infeed direct current system transmissionsystem in future. Overvoltage is very critical for power transmission stability and engineering feasibility of hybrid-HVDC transmission system. It is necessary and significant to research overvoltage control strategy on hybrid-HVDCtransmission system. Firstly

the operation and overvoltage mechanism of hybrid-HVDC transmission system are ana-lyzed in this paper. Above this

overvoltage impact factors of hybrid-HVDC transmission system are comprehensivelyanalyzed. Based on this

the overvoltage control strategy would is proposed in detail. Finally

LCC-MMC hybrid-HVDC transmission system and model are built by PSCAD/EMTDC

and the overvoltage control strategy is simulat-ed. According to the analysis and result

the main factor of HVDC transmission system overvoltage is the chargingcircuit of sub-module

after MMC blocking. In addition

the overvoltage level of hybrid-HVDC transmission systemcould be suppressed effectively by LCC current order fast response strategy.