The Improvement of Small Interference Synchronous Stability of Photovoltaic Grid-connected Converters

Virtual synchronous generator (VSG) can be effectively implemented to improve the stability of new energy grid-connected inverters. Power oscillation can be effectively suppressed by adjusting the moment of inertia and damping of VSG according to the operating state. In this paper, a phase compensation strategy for PLL is proposed to reduce its negative damping to enhance the stability of small disturbances. First of all, the grid-connected inverter model controlled by virtual synchronous generator is established, and the damping torque model including the converter and the complete control dynamics of the grid is derived. Then the SISO stability criterion of grid-connected system is obtained based on damping torque model. The influence of damping coefficient on the stability of single-stage three-phase PV grid-connected converter system is analyzed. Finally, the simulation results show that the proposed method can improve the stability of small disturbance.