Modeling and Stability Analysis of Grid-Forming Inverters Based on Synchronization Control Equivalence

As the proportion of renewable energy sources and the proportion of power electronic devices in the power system are continuously developing, grid-connected inverters with frequency and voltage regulation capability have become one of the important needs of the power grid. The power grid needs inverters with grid-connected capability that can provide the necessary support to improve the grid-friendliness of renewable energy sources, therefore, the study of grid-forming inverter characteristics is necessary. In this paper, a method for studying the synchronization stability of grid-forming inverters is provided in terms of the duality characteristics between droop control and phase-locked loops. The droop control is equated to a phase-locked loop-like form. The sequence impedance modeling is used to analyze the inverter's stability. Firstly, a phase-locked loop-like control system of the droop-controlled inverter is established. Then, according to the control method after the equivalence, the sequence impedance model of the inverter is derived and verified. Finally, the stability of the inverter system is analyzed and the theory is verified by simulations.