Research on an Active Damping Method under Weak Grid Condition with Adaptive Impedance Ability

With high penetration of renewable energy in power grids, the impedance of power electric inverters cannot be ignored, thus resulting a weak inductivity in power grid. As renewable power energy conversion devices, the control characteristic of grid-connected inverters determine the stability of the entire power grid. The grid will present inductive behavior and result the characteristic in point of common coupling week grid behavior. In weak grid, LCL filter is easily affected by system environment, such as grid impedance, control delay, etc., which may endanger the safety and stability of the converters which connect to the power system. This paper focuses on how active damping method can adapt to the wide range of changes in grid impedance under weak grid conditions while meeting its own stability, so as to meet the stable operation requirements of the power grid system. The stability of LCL grid-connected inverter under both ideal and weak grid condition will be firstly analyzed, and the causes of instability under weak grid conditions are studied. Aiming at the problem that LCL filters are easy to cause system instability under weak power grid condition, an active damping method with adaptive impedance is proposed in this paper, the adaptive ability of the impedance of gird-connected inverter is improved, so as the stability of the entire system. Finally, the effectiveness of the method is verified by simulation using MATLAB Simulink.