Instability Analysis of Grid-Connected Inverters During Low-voltage-ride Through Process

Abstract:
During the low voltage ride-through (LVRT) process, it is found that grid-connected inverters may experience instability. The reason is that when outputting the reactive current according to the grid-voltage dip value, the large grid impedance may lead to the root of the characteristic expression moving outside the unit circle. A low-pass filter (LPF) with a designed cut-off frequency is proposed to be used with the voltage magnitude detection module. It is revealed that LPF will expand the variation range of grid impedance and enhance the stability of the system. The simulation results have verified the correctness of the theoretical analysis.