E-Drive SiC MOSFET Inverter with Self Calibrating VON-based Junction Temperature Estimator

Monitoring junction temperature is of key importance in SiC MOSFET power converters, to guarantee their reliability. A feasible method for estimating the junction temperature of a power MOSFET is to take advantage of the correlation between junction temperature and conduction resistance. However, this approach requires a preliminary calibration of the V_ON characteristic as a function of the junction temperature of the device. This is usually performed offline through dedicated laboratory equipment. This work proposes a novel method for measuring the on-voltage versus temperature characteristic directly on the drive, with the motor already connected to the inverter, thus avoiding the necessity of a dedicated test rig. The commissioning procedure starts with a self-heating phase, followed by the R_ON measurement stage. A polynomial fit is proposed to extrapolate the R_ON characteristic out of the domain of measured temperatures. The obtained data can then be used for online estimation of the junction temperature of the six MOSFETs on board of a PWM operated three-phase inverter.