An improved RCD snubber for solid-state circuit breaker protection against bus fault in low-voltage DC microgrid

An improved RCD snubber for solid-state circuit breaker (SSCB) is proposed in this paper in a low-voltage DC microgrid to protect SSCB against overvoltage caused by its tripping at the occurance of a DC-bus fault. Instead of relying mostly on the snubber capacitor to absorb the fault energy like commonly-used RCD snubbers, the proposed RCD snubber uses the snubber diode and an additional snubber resistor to form a separate path, which allows most of the energy to exhaust itself away from the snubber capacitor. In this way, the overvoltage across SSCB can be suppressed without increasing value and capacity of snubber capacitor, while the fault energy can also be quickly spent. Snubber process is discussed detailedly at a line-to-line fault to prove its effectiveness. Also, a design method is presented because former studies on parameter design of RCD snubber usually aim for converter appliance and cannot be directly applied on the proposed RCD snubber, which must be able to operate under fault current and thereby lays more stress in the peak value damping of overvoltage instead of quick suppression. Finally, simulations are conducted to prove its effectiveness in overvoltage suppression and fault current absorption.