An Online On-State Voltage Measurement Circuit With Series Diode Clamp for SiC MOSFETs

The condition monitoring of SiC MOSFETs is significant for the reliability of the power electronic system. The on-state drain-source voltage( $V_{\text{DS}-\text{on}}$ ) of SiC MOSFETs contains the temperature information and reflects the health state. It is essential information for the junction temperature monitoring, loss calculation, and health state evaluation of SiC MOSFETs. A measurement circuit with a voltage clamp branch is proposed in this paper to solve the problems of large errors, complex structure, and low reliability of traditional $V_{\text{DS}-\text{on}}$ measurement circuits. The proposed circuit uses several series diodes as the clamp branch, and the voltage peak of the input circuit is suppressed by setting a reverse parallel fast recovery diode. Simulation and experimental results show that the proposed circuit has high accuracy and reliability. Combined with the offline calibration of the linear relationship between $V_{\text{DS}-\text{on}}$ and junction temperature, the proposed circuit can be used for the online monitoring of the junction temperature of SiC MOSFETs. Lastly, the optical fiber temperature sensor is used to verify the measurement results of the proposed circuit for junction temperature monitoring, which shows that the proposed circuit is highly accurate and feasible for junction temperature monitoring.