Evidence of Gate Voltage Oscillations during Short Circuit of Commercial 1.7 kV / 1 kA IGBT Power Modules

This paper analyzes the evidence of critical gate voltage oscillations in 1.7 kV/1 kA Insulated-Gate Bipolar Transistor (IGBT) power modules under short circuit conditions. A 6 kA/1.1 kV Non-Destructive Test (NDT) set up for repeatable short circuit tests has been built with a 40 nH stray inductance. A large amount of measurements have been acquired on commercial IGBT modules evidencing gate voltage oscillations under short circuit conditions. To tackle this problem, similar tests have been performed on a modified version of the same modules with two parallel sections and one single section. Mutual oscillations between two parallel sections have been evidenced, whereas single section configuration does not exhibit such instability. According to the experimental observations, it can be concluded that these oscillations are initiated by the paralleling of IGBT chips and sustained by a positive feedback involving the stray impedances of the module itself.