In the reliability study of modular multilevel converter（MMC）

the research of key devices mainly focuses on the degradation of physical performance

but its results are not well used in the system level reliability evaluation. In order to correlate operating conditions with device aging and reliability

a reliability evaluation method of device aging based on MMC task profile is proposed. Firstly

the power loss of MMC key devices is deduced. Combined with the mission profile

the rainflow counting algorithm is used in the junction temperature calculation. According to the linear fatigue cumulative damage principle

the damage and lifetime of the devices under the electric heating coupling condition are obtained. According to the aging problem of the device

the aging phenomenon of the device is more obvious than that of the varying working stress under constant high stress by analyzing the aging increment under different working conditions. The reliability analysis method based on exponential distribution is improved

which provides a reference for the replacement of module components in regular maintenance.