Virtual synchronous generators (VSG) technology is widely used in grid-connected and multi-machine parallel control strategies for inverter systems because of its ability to simulate synchronous generators and make distributed power sources also have inertia and damping coefficients. To avoid the shocks and oscillations in the transient process that destabilize the VSG system when the external disturbances are large

an improved control strategy with adaptive rotational inertia and damping coefficients is proposed in this paper. By analyzing the transfer function of the VSG system

the dynamic response curves of the system under different conditions are obtained

and the values of virtual inertia and damping coefficient are initially established. On the basis of the traditional adaptive strategy

the damping ratio of the system is considered and the functions of the damping coefficient and inertia are determined; and combined with the results of the analysis of the power angle characteristics

the positive and negative values of the angular velocity variation and the rate of variation are incorporated into the consideration of the values of the rotational inertia and the damping coefficient

and the adaptive value conditions are further subdivided

and an improved adaptive strategy is proposed. The VSG model of the inverter system is built on MATLAB/Simulink

and a two-machine parallel experimental platform is built to verify that the improved strategy can significantly improve the active power and frequency stability and reduce the loop current in the dynamic process of the parallel system compared with the fixed parameters and the traditional adaptive strategy.