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To improve the connection efficiency to grid of distributed power sources, and solve the problems of insufficient damping and inertia in inverter grid connection, an inverter control method was investigated to realize traditional synchronous generator's function, which was named as virtual synchronous generator (VSG) technology. Based on the role of phase locked loop (PLL) in virtual synchronous generator, the pre-synchronization control method was proposed based on virtual power. The secondary frequency modulation and the secondary voltage regulation functions were simulated in the power loop. The output value compensated the loss of active power and reactive power through inertia link, and the control parameters were flexibly adjusted according to power levels. Regarding the voltage and current on the VSG generator side, the PR control method was used to increase the constraint on the electrical value for preventing grid connection failure. The topology structure and the mathematical model of VSG were analyzed, and the improved control method of VSG was given. A corresponding simulation model was established to verify VSG control effect from two aspects of pre-synchronous grid-connection and grid connection stability under mutation load. The results show that the improved VSG control can reduce the complexity of grid-connected inverter and the oscillation frequency of output power and suppress the current impact on the grid side, which makes the inverter follow the dynamic change process of power grid at all time. [ABSTRACT FROM AUTHOR]