Research on inverter droop control strategy based on virtual impedance

In the parallel operation system of the low-voltage microgrid inverters, due to the difference of line impedance and other factors, the equivalent output impedance of inverters is mostly resistive or resistive-inductive, and the use of traditional sag control will make uneven reactive power distribution and power circulation in the parallel inverters. Based on the traditional sag control strategy, a sag control strategy based on adaptive virtual impedance is proposed to adjust the inverter equivalent output impedance to be inductive, which improves the accuracy of reactive power allocation and suppresses the power circulating current; meanwhile, the adaptive virtual impedance follows the changes of the system voltage and current, and continuously adjusts the impedance value on-line to make up for the system voltage landing. The inverter parallel operation simulation model is built in MATLAB/Simulink, and the simulation results verify the effectiveness of the methods.