Cascaded Operation of SiC JFETs in Medium Voltage Solid State Circuit Breakers

This paper reports cascaded operation of 1200V normally-on SiC JFETs in a solid state circuit breaker (SSCB) designed for medium voltage DC systems. The SSCB detects the short circuit fault by sensing the voltage rise between its two terminals and consequently uses this fault condition to power up the control circuit to turn and hold off the SiC JFETs to interrupt the fault current. Voltage sharing and balancing among the cascaded SiC JFETs during the fault current interruption process are important design considerations. Both simulation and experimental work are performed to identify an optimal circuit solution. The final SSCB prototype experimentally demonstrated a fault current interruption capability up to 125 amperes at a DC bus voltage of 1000 volts within 2.5 micro seconds.