Normalization of Capacitor-Discharge I2t by Short-Circuit Fault in VSC-Based DC System

In the voltage-source-converter-based dc system, the short-circuit current increases rapidly due to neighborhood dc-link capacitance. The protection system using a high-speed fuse has been applied in the industry to protect before the current freewheeling that ruins a semiconductor device. For proper protection system design, the capacitor-discharge
I
²
t
must be analyzed and set higher than the melting
I
²
t
of the fuse by securing sufficient capacitance. However, due to the implicit characteristics of the
I
²
t
function, it is difficult to calculate the required capacitance directly considering unknown fault resistance. In this article, the normalized
I
²
t
map of capacitor-discharge is presented as a calculation reference. After calculating the base values, the normalized
I
²
t
value can be calculated easily from the map without complicated formula. Since it is expressed as a function of the damping factor (half of the normalized resistance) and normalized capacitor's voltage, it helps
I
²
t
design with the range of fault resistance and voltage drop simultaneously. The proposed normalization and its result were verified through the experimental tests under various fault resistance.