With the development of the HVDC-flexible technology

the performance advantages of voltage sourceconverter have been more widely recognized

voltage source converter technology based on modular multi-level con-verter（MMC）has been widely used in China

Nan’ao

Zhou’shan multi-terminal HVDC-flexible project and Lu’xiasynchronous interconnection HVDC-flexible project have been completed and put into operation

±420 kV Yu’eback-to-back interconnection project

±500 kV Zhang’bei renewable energy HVDC-flexible demonstration projecthas started construction

±800 kV Wu’dongde to Guang’dong and Guang’xi multi-terminal HVDC project has en-tered the implementation stage of the project. The modular multi-level converter（MMC）valve is one of the main de-vices of the HVDC-flexible transmission system. To ensure safe and reliable operation of the HVDC-flexible transmis-sion system

the converter valve must be strictly examined in the type test. The operational test

as one of the impor-tant items in type tests

examine the adequacy of the converter valve with regard to current

voltage and temperaturestress in conducting state and at turn-on or turn-off moments under the worst repetitive stress condition. According tothe actual operational condition of voltage source converter valve based on MMC

this study proposed an operationaltest method

and constructed a test circuit to conduct operational tests of the MMC valve for actual HVDC-flexibleproject. The results show that the proposed test method and test circuit can carry out operational tests of the voltagesource converter valve

and the test results meet the relevant standards of IEC 62501:2017

GB/T 33348—2016

and DL/T 1513—2016.