For the inverters connected to the weak grid

the typical low voltage ride-through(LVRT)control methods may result in instability of the system during severe voltage sag on the remote grid side. The instability mechanism is different from that during the voltage sag at the point of common coupling. By taking a single inverter infinite system as an example

this paper develops a quasi-steady model of the system. The instability mechanism of the inverter is analyzed from the factors of voltage sag level

line inductance

and gain coefficient of LVRT. Then the small signal model of the system is established. The analysis shows that the inverter may also have the problem of small-signal stability when the quasi-steady-state model is stable. Finally

the rationality of theoretical analysis is verified based on the MATLAB/Simulink simulation.