Research on Voltage Sag Properties of Medium-Low Voltage DC Distribution System

Recently, the quick development of DC distribution system (DCDS) has attracted increasing attention, and it has good technical advantages to accommodate DC renewable energies and DC power loads. However, the study of the power quality issue of DCDS is still at an initial stage, and little work addresses the voltage sag properties of a medium-low voltage DCDS. In this paper, typical DC short-circuit faults and DC load change are considered to investigate the voltage sag performances of the medium-low voltage DCDS. Related theoretical analysis of the DC voltage dip is implemented, and using MATLAB/Simulink, a detailed digital simulation model of a 20 kV class DCDS is established to check the voltage sag characteristics. From the simulation findings, the DC pole-to-pole fault and the pole-to-ground fault will cause visible voltage dips, and especially when the faults happen at the medium-voltage bus, the voltage levels of the entire DCDS will face serious falls. Regarding the sudden change of the DC load, it is concluded that the main dynamic influence appears at the low-voltage bus side, and the medium-voltage stabilization is favorably obtained.