Impact of Cooling System Capacity on Lifetime of Power Module in Adjustable Speed Drives

In this paper, the impact of the cooling system capacity on the reliability of power modules in power converters is studied. Since the different cooling system capacities lead to different absolute junction temperatures under the same mission profile (MP) of power converters, the lifetimes of the insulatedgate bipolar transistor (IGBT) modules under different mean junction temperatures are assessed by means of an advanced power cycler. Then, the mean junction temperature dependent lifetime factor is modeled based on 18 power cycling test results using Weibull analysis. Finally, the influence of the cooling system capacity on the reliability of the power module is validated by performing a case study of the motor drive system, where the lifetime of the IGBT module is estimated and compared under the two MPs with different average heat-sink temperatures. This study shows the importance of the cooling system capacity not only with respect to the overstress failure of the power device but also with respect to the wear-out failure of the power module and also proposes a method to select the proper heat-sink temperature in order to achieve specified reliability.