Stability Analysis and Enhancement of Parallel Grid-Connected Inverters with LCL Filter in A Weak Grid

This paper aims to analyze and enhance the stability of parallel grid-connected inverters. The presence of power electronics converters in weak grids, where the short circuit power is low or the ratio of reactance to path resistance is high, can cause voltage and current instability at the point of common coupling (PCC). Therefore, the grid impedance plays a major role in destabilization of grid-connected inverters. The impact of grid impedance on parallel inverters is even worse. In order to address the aforementioned problem, this paper proposes a method based on implementation of a virtual impedance generated according to a straightforward algorithm in the control loop, which increases the stability margin and reduces the dependence on the grid impedance. To verify the effectiveness of the proposed stabilizing method, pole locations of the closed-loop system are analyzed, and simulation results are obtained in MATLAB and Simulink software.