Analysis on asymmetric fault current of inverter interfaced distributed generator

Abstract

Fault characteristics of inverter interfaced distributed generator (IIGD) are determined by its grid-side converter. To deduce the fault current of IIDG is to analyze the current response under the action of grid voltage sags. To enhance the low voltage ride through (LVRT) ability of IIDG when asymmetric fault occurs, the dual current control strategy is widely used. In this paper, the positive and negative sequence current expressions were deduced based on the dual current control strategy and the influence factors were analyzed based on the expressions. When the amplitude of the fault current is higher than the maximum value of the converter can transfer, a new fault current calculation method was proposed. Theoretical analysis and simulation on PSCAD verified that the d-axis components of positive and negative sequence current meet second order response and the q-axis components are zero. The steady-state value of positive and negative sequence current is determined by the unbalance degree of grid and the transient process of fault current is determined by the control parameters of the grid-side converter. The conclusions are of great significance to relay protection of the grid with HDG.