1.Hubei Key Laboratory of Power Equipment & System Security for Integrated Energy, Wuhan 430072, China;2.School of Electrical Engineering and Automation, Wuhan University, Wuhan 430072, China;3.Electric Power Research Institute of State Grid Hubei Electric Power Co., Ltd., Wuhan 430070, China

With the large-scale integration of renewable energy generators, the power system faces a severe risk of transient synchronous instability. The grid-forming converter controlled by the virtual synchronous generator (VSG) simulates the dynamic characteristics of the synchronous generator to achieve synchronization with the power grid, which has good frequency and voltage support ability. However, the existing transient stability criteria based on the equal area criterion and the energy function cannot fully capture the effects of virtual inertia and damping on the transient synchronous stability of VSG, which are unable to accurately quantify the stability boundary. Therefore, this paper proposes a transient synchronous stability analysis method of VSG based on the iterative equal area criterion. Based on the principle of conservation of energy, an iterative algorithm is designed to obtain the frequency-power angle distribution function of the converter under critical stability conditions. Thus, the effects of VSG inertia and the work done by the damping term on the acceleration and deceleration areas of the transient process are accurately quantified. By comparing the sizes of transient stability regions with different controller and grid parameters, the influence of parameters on the transient stability boundary is quantified. Finally, the MATLAB/Simulink simulation and the RT-LAB hardware-in-the-loop experiments are used to verify the effectiveness and superiority of the proposed stability analysis method. Compared with the conventional equal area criterion and the Lyapunov method which completely ignore or only conservatively consider the influence of damping work, the conservatism of the proposed iterative equal area criterion is extremely low. Compared with the time domain numerical method, the computational efficiency of the proposed iterative equal area criterion is also significantly improved. Therefore, the proposed method can realize the accurate and fast calculation of the transient stability boundary.