A Simple Impedance Reshaping Method for Stability Enhancement of Grid-Following Inverter Under Weak Grid

The conventional vector current control (VCC) scheme has been widely used in the grid-connected inverter systems. However, it suffers from power limitation problems under weak grid conditions. This paper reveals that the dynamic effect of the phase-locked loop (PLL) is the main reason for destabilizing the small-signal stability of the grid-following inverter. The positive feedback introduced by the PLL can be observed from the small-signal control structure. Reshaping the converter output impedance can counteract the positive feedback and reduce the negative resistance in the impedance model. A novel impedance reshaping method is proposed in this paper, which can enhance the small-signal stability and extend the stability range of the system. Simulation results verify the effectiveness of the proposed method.