The virtual synchronous generator(VSG)has similar external characteristics to the synchronous generator(SG). The VSG has the same instability mechanism as the SG under the large disturbance. However

compared with the SG

the inverter of VSG is affected by the current limit

whose power-angle curve is different with SG as well. Meanwhile

the damping coefficient of VSG is much larger than that of SG and the power-angle stability of VSG cannot be easily determined. Considering the integration of the VSG and infinity system

the power-angle curve transformed from saturated current to unsaturated current is described and the strong damping of coefficient characteristic of the VSG is analyzed firstly. Then

the strong time-varying characteristic of VSG systems is illustrated. The method which can judge the stability of the VSG system is put forward. Finally

based on the PSCAD software

the simulation is conducted to verify the reasonability of the method mentioned above.