Small Signal Model and Stability Analysis of LCL Grid Connected Inverter under Weak Grids

The problem with connecting LCL grid connected inverters (LCL-GCI) to weak grids is that inverter operation is often unstable. And another problem is that it is difficult to analyze the stability of the LCL-GCI due to the nonlinearity of the system. Therefore, this paper presents a small signal model of LCL-GCI for analysis of inverter stability. The model is derived from the state space method to linearize the model around its operating point, used to carry out the poles of the LCL-GCI system to determine the system stability with a change of its parameters including weak grids conditions. A change of LCL-GCI and the grids parameters effects the stability of the system especially a weak grid conditions the grids impedance is increasing. The simulation shows the movement of system pole in s-plane demonstrates the system stability when LCL-GCI parameters and grid impedance are changed. Although the LCL-GCI is unstable under weak grids, the improvement parameter methods by increase LCL filter parameter and reduce the controller gain can bring the system stable again.