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A Digital-Controlled SiC-Based Solid State Circuit Breaker with Soft-Start Function for DC Microgrids

This paper introduces a digital-controlled, SiC MOSFET based, autonomously operated 380V/20A solid state circuit breaker (SSCB) that features a soft start function in addition to basic short circuit protection function. The SSCB offers three distinct operation states: ON, OFF, and PWM Current Limiting (PWM-CL). While the conventional ON/OFF states allow the SSCB to conduct normal load currents or interrupt fault currents, the PWM -CL state allows the SSCB to gradually charge the input capacitors of electronic loads at a limited current level during load startup. The SSCB can switch from the PWM-CL state to the OFF state if a true short circuit fault is detected. In the PWM -CL state, a variable frequency PWM control technique is proposed to optimally operate a buck converter for soft start and short fault detection. The controller design of the new SSCB combines the flexibility of a DSP with the µs-scale ultrafast response time of an analog-like overcurrent detection circuit. The paper analyzes the relationship between the PWM frequency and circuit parameters, load voltage, and load resistor. The new SSCB is prototyped and experimentally verified.