Online Vce measurement method for wear-out monitoring of high power IGBT modules

A simple Vce online monitoring circuit is presented in this paper. It allows an accurate wear out prediction of IGBT modules, in high-power applications, during normal converter operation. Bipolar measurement allows monitoring of both IGBT and antiparallel diode. The circuit uses two serial connected diodes to sense the Vce voltage with millivolt accuracy. One diode acts as a protection to block high DC voltage present on input terminals. When the device is conducting the voltage on the second diode is measured to compensate for the voltage drop on the protection diode thus eliminating voltage offset due to diodes' forward voltage temperature dependency. Using four diodes one can monitor voltages on all power devices in a converter leg.