An earth fault current limiter using a modular multilevel inverter for smart grids operation

Abstract

In this paper, a modular multilevel inverter is proposed as an earth fault current limiter. The modular multilevel inverter is designed to limit the earth fault current following a preset current reference. The topology, structure, and functionality of the modular multilevel inverter are introduced. The inverter is designed to be sourced by charging capacitors from the grid itself. The modular multilevel inverter acts as an adjustable impedance to decrease the earth fault current passing in the grid down to safe levels. The control system of the inverter is designed to achieve the desired impedance needed to reduce the earth fault current to predetermined values, which do not cause any damage to the grid or its protection components, but sufficient to activate the protection system. Besides, the modular multilevel inverter does not need very high voltage rating devices, as the maximum voltage rating of each switch does not exceed 650 V. Such a modular multilevel inverter has a low Total Harmonic Distortion in the grid’s voltages, even with low values of the passive components of the coupling filter. Moreover, with the proposed system, the grid can continue supplying the load with the needed power even during the ground fault. Simulations are carried out using MatLab/Simulink platform and various results demonstrate the ability of the proposed system in controlling the ground fault current.