Noncontact Monitoring of IGBT Turn-OFF Time Using PWM Switching Ringing for Inverter-Fed Machine Systems

Turn-off time is an important condition parameter for insulated gate bipolar transistor (IGBT), which could provide useful information on the device junction temperature and its state of health. Currently, it is measured directly from the IGBT collector-emitter voltage V_ce or indirectly from the gate side, which may cause problems of safety and complexity for a power converter operating in a harsh electromagnetic environment. To address the challenges, this article proposes a noncontact method to monitor the IGBT turn-off time from the PWM switching ringing in the converter output current. First, a phenomenon is observed that there are two switch-over points in the switching ringing current corresponding to the transition of IGBT turn-off voltage. Analytical analysis is performed with a high-frequency (HF) equivalent circuit to investigate the mechanism of the one-to-one temporal relationship. Then, the noncontact condition monitoring (CM) scheme including the HF switching ringing current sensor and the framework of CM system is devised. Finally, experimental work is carried out to validate the theoretical analysis and the effectiveness of the method. Research results show that the turn-off time of multi-IGBTs can be effectively extracted at the terminal of converter during system normal operation with electrically isolated safety.