Using Redundant IGBT Device as a Temperature Sensor—Online Monitoring System of Thermal Parameters for NPC Three-Level Inverters

Neutral-point-clamped (NPC) three-level inverter has been widely used in the field of medium- and high-voltage power inverters, and the existence of redundant insulated gate bipolar transistor (IGBT) devices in specific topology brings the possibility of online monitoring for thermal reliability. First, a small-current thermally sensitive electrical parameter (TSEP) circuit integrated on the driver side is used to obtain the junction temperature of the redundant IGBT device at strictly selected injection moment, which provides timely and effective overtemperature protection by reasonably evaluating the upper limit temperature. Furthermore, by choosing the redundant IGBT device as the reference temperature point, the coupled thermal impedance network model can be effectively simplified and improved, thereby realizing faster online junction temperature estimation of the remaining power devices from the controller side. By cleverly utilizing the redundant IGBT devices, the study shows that the proposed thermal parameter monitoring system can achieve truly nonintrusive thermal reliability online monitoring without the need for intrusive modification of the module or additional temperature sensors, on the premise of not affecting the normal operation of the module and the equipment.