In-situ evaluation of inflection-point current for temperature independent condition monitoring of IGBT in two level three phase AC motor drives

The on-state collector-emitter voltage drop (
v_CE,on
) of an IGBT as an indicator for package related failures has been very well studied in literature. To obtain measurements at the same condition consistently remains a challenge as
v_CE,on
varies with the junction temperature and current levels other than at inflection point current level (
I_inflection
). The measurement of the
v_CE,on
at the evaluated
I_inflection
is effectively decoupled from the effect of junction temperature such that the true state-of-the-health of the IGBTs can be assessed independent of temperature influence on
v_CE,on
. In this paper, a new method has been proposed for in-situ evaluation of
I_inflection
in two level IGBT based three phase (3ɸ) AC motor drive without expensive pre-characterization of IGBTs. The key advantage of the proposed method is in-situ evaluation of
I_inflection
with existing hardware and without lowering the DC-link bus voltage and shorting the two IGBTs on the same phase leg. The method eliminates the need for calibration using parametric semiconductor analyzer and thus, provides inexpensive and faster estimation of
I_inflection
.