A Model Based LCL-Type Grid Connected Converter Under Balanced and Unbalanced Faults in a Micro-Grid Distributed Generation

Abstract

This research was conducted to verify the significance of the LCL-filter on the grid current and the impact of variable fault resistance values on the reactive power genereated in a grid-tied inverter. The stability of LCL-type grid connected inverter with capacitor current feedback in active damping state was evaluated in this paper. The effects of balanced and unbalanced grid faults on the active and reactive power was studied through simulation at different fault resistance values of 0.00025Ω and 2.5Ω. The FFT waveforms showed that THD values of 48.56% and 38.45% were achieved for the grid voltage at 0.00025Ω and 2.5Ω fault resistance while THD values of 9.50% and 4.41% were obtained for the grid current at a varied current feedback coefficient (K<SUB>CP</SUB>) of 4.75 and 14.75. Simulation results also showed that a very negligible real and reactive power was gained with a zero grid voltage within the fault zone at 0.00025Ω fault resistance. At a 2.5Ω fault resistance, a voltage sag was produced which accounted for the transient response in the real power generated and reactive power absorbed during the fault period. The result obtained from the root-locus plot showed that the loci for the derived LCL-filter current transfer function intersected at +j 8.734 and -j 8.734 which makes the system marginally stable All simulation procedures were realized in MATLAB/SIMULINK 2015.