Self-Calibration Technique for Junction Temperature Estimation of SiC MOSFET Inverters Loaded with Synchronous Reluctance Motors

SiC devices have pushed the boundaries of power electronic conversion to new limits of power density and efficiency, but they also require appropriate thermal management. The conduction resistance of a SiC MOSFET is an indirect indicator of its junction temperature, provided that the R-ON versus temperature and current characteristic of the device is preliminarily mapped. Such R-ON map is normally obtained using dedicated test rigs, with the inverter connected to a custom inductive load. In this work, the R-ON maps of the power devices of a 3-phase Voltage Supply Inverter are obtained via self-calibration with the converter already connected to the target synchronous reluctance motor, without requiring rotor movements nor dedicated measurement equipment. The proposed procedure consists of a preliminary self-heating stage followed by R-ON mapping through current pulses along the zero-torque directions of the rotor reference frame. The connection to the target motor reduces the measurement domain in terms of maximum current and temperature with respect to the custom load. A polynomial model is used to extrapolate the R-ON characteristic out of the measurement domain, showing high estimation accuracy. Preliminary experimental results are presented.