Overcurrent induced by DC fault may cause great electromagnetic force and temperature rise on the busbar of modular multilevel converter（MMC） submodule

which may result in permanent failure of the busbar. In order to explore the failure mechanism of the busbar under DC fault

we analyzed the electromagnetic-temperature-mechanical coupling field of the busbar based on DC fault calculation and multiphysical field simulation. First of all

based on the arm equivalent model

we accurately calculated the arm fault current

analyzed the influence of fault time on the arm fault current

and obtained the most serious fault current magnitude that may occur on the submodule busbar. Secondly

the electromagnetic force and Joule heat of each part submodule busbar were modeled

and the temperature rise and stress distribution of each part of busbar were solved. The calculation results show that the temperature rise of the busbar is negligible

but the mechanical stress is large

the deformation is serious

and the axial force on the bypass thyristor bolts is the largest of all

which may cause bolt detachment failure. This paper provides useful information for MMC submodule busbar failure analysis and design.