School of Electrical Engineering, Wuhan University, Wuhan 430072, China

The virtual synchronous generator(VSG)realizes the virtual inertia control of the converter by simulating the swing equation of traditional synchronous generator, which also suffers the transient instability under large disturbance. This paper analyzes the transient stability of the VSG connected to the infinite bus. Firstly, the large signal model of the inverter controlled by the VSG is established and the system order is reduced based on the singular perturbation theory. The correctness of the model is verified by comparison with the electromagnetic transient simulation model. On this basis, the cell mapping method is introduced to analyze the global nonlinear characteristics of the reduced order model. The region of attraction in the phase plane, which is represented by the virtual angular velocity and the virtual phase angle is found and the key factors that affect the stability of the VSG under large disturbance are analyzed. The results of the analysis are compared with the results of the small signal analysis, which shows that system parameters, such as the internal impedance of the power grid, the feeding power, the virtual inertia, the damping coefficient and the filter parameters, have significant influences on the transient stability of the VSG under large disturbance. Finally, based on MATLAB/Simulink simulation, the rationality of the proposed method is verified.