Fault-Current-Limiting Protection Circuit and PWM-Based Soft-Reclosing Method for Protective Coordination in DC Distribution Systems

This paper presents a DC short-circuit protection circuit and a PWM-based soft-reclosing method for protecting power converter stations in DC distribution systems. The proposed protection circuit limits the rapid increase of fault current using a current-limiting inductor, thereby reducing the current stress on the protection switch before it completes its turn-off operation and preventing full discharge of the DC-link capacitor during short-circuit faults. Additionally, a compensation capacitor is applied to reduce the output voltage sensitivity introduced by the inductor, while a damping diode is employed to suppress LC resonance between the inductor and capacitor. Moreover, the proposed soft-reclosing method gradually increases the duty ratio of the protection switch after fault interruption, thereby suppressing inrush and reclosing currents during system restoration. Experimental results verify that the proposed method enables stable recovery under temporary faults while ensuring safe re-opening in the presence of permanent faults.