Solid-state Over-current Protection for Industrial DC Distribution Systems

We describe a concept for circuit protection and fault current limitation in DC power systems based on the use of solid-state power switches. The approach could be useful in the increasingly widespread application of DC power distribution networks. During normal operation the power switch is always “on”. During faults, the gate of the solid-state switch is pulse modulated to prevent the circuit current from exceeding a predetermined limit. This lowers the demand on the solid-state switches to withstand and interrupt the fault current and thus makes it possible to use commercially available solid-state switches. The described architecture enables loads in non-faulted parts of the system to ride through the fault current-limiting process unperturbed. Simulations demonstrate the effectiveness of the strategy and a low power prototype validated the simulation model. The interactions between the protection switches and the upstream converters were studied, and the design equations for the circuit parameters are derived. Simulations and experiments demonstrate that the protection circuit provides a fast and potentially maintenance-free protection solution for high power-density DC systems. This technology is especially significant for applications related to spacecraft and shipboard DC power systems. Nomenclature A = amplitude of triangle carrier D = duty cycle I0 = full prospective short circuit current If = fault current Imax = preset current threshold iL1 = current through Load1 K = gain Sl = rising edge slope St = falling edge slope Tl = rising time Tt = falling time VD1 = forward voltage drop of diode D1 VDC = load bus voltage