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 (vCE,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 asvCE,onvaries with the junction temperature and current levels other than at inflection-point current level (Iinflection). The measurement of thevCE,onat the evaluatedIinflectionis 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 onvCE,on. In this article, a new method has been proposed for in situ evaluation ofIinflectionin two-level IGBT-based three-phase (3Φ) ac motor drive without expensive pre-characterization of IGBTs. The key advantage of the proposed method is the in situ evaluation ofIinflectionwith existing hardware 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 a parametric semiconductor analyzer and thus, provides an inexpensive and faster estimation ofIinflection.