IGBT Turn-Off Time Monitoring in AC/DC Converter Using Less Sensors With Lower Sampling Rate

The turn-OFF time of insulated-gate bipolar transistor (IGBT) is a critical parameter indicating the junction temperature and state of health. Monitoring turn-OFF time of all six IGBTs in a three-phase AC/DC converter require six dedicated sensors and sampling rate typically exceeding 250 MHz, resulting in substantial hardware costs. A novel method is proposed to monitor turn-OFF time of all six IGBTs in AC/DC converters with only two sensors. It is achieved by measuring two line-voltages and converting them to collector-emitter voltages (Vce), instead of direct Vce measurement of each individual IGBT. Meanwhile, the measurement error of turn-OFF time becomes large in the condition of lower sampling rate. An error compensation method with convex hull algorithm is put forward to improve measurement accuracy. An AC/DC converter prototype is developed for experimental verification. Experiment results show that the proposed method can achieve turn-OFF time measurement error within 4 ns for all six IGBTs, while requiring 67% less sensors and reducing sampling rate requirement by 90%.