Improved Short-Circuit Protection Scheme with Fast Fault Detection for SiC MOSFET

Wide-band-gap devices switch fast, leading to improved efficiency and compactness. However, since their fault-current withstand capability is reduced, these require fast detection of and protection from faults. Reduction of fault detection time in desaturation-based protection requires reducing the blanking capacitance. But, this results in large voltage oscillations across the blanking capacitor, leading to spurious trip of the power converter, particularly during device turn-off and discontinues current mode (DCM) operation of the converter. This paper proposes a means to achieve fast fault detection through low blanking capacitance, ensuring no spurious converter trip. The proposed fault-detection and protection scheme is successfully demonstrated for very low blanking capacitance, contributed to only by parasitic capacitances. Worst-case detection times for fault under load (FUL) and hard switching fault (HSF) are estimated. Low detection times are demonstrated experimentally for both types of faults. The proposed protection scheme is deployed successfully in an 800-V(dc), 50-A(rms), 50-kHz asymmetric H-bridge converter for driving high-speed switched reluctance machine.