In Situ Evaluation of Inflection-Point Current for Temperature-Independent Condition Monitoring of IGBT in Two-Level Three-Phase AC Motor Drives

Abstract

The on-state collector-emitter voltage drop ( $v_{\text {CE,on}}$ ) 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 $v_{\text {CE,on}}$ varies with the junction temperature and current levels other than at inflection-point current level ( $I_{\text {inflection}}$ ). The measurement of the $v_{\text {CE,on}}$ at the evaluated $I_{\text {inflection}}$ 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 $v_{\text {CE,on}}$ . In this article, a new method has been proposed for in situ evaluation of $I_{\text {inflection}}$ in two-level IGBT-based three-phase ( $3\Phi $ ) ac motor drive without expensive pre-characterization of IGBTs. The key advantage of the proposed method is the in situ evaluation of $I_{\text {inflection}}$ with 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 of $I_{\text {inflection}}$ .