Converter-driven Stability of Grid Following Inverters: the Impacts of Damping and Fault Ride-Through

The interaction of grid following (GFL) inverters with a weak grid raises risks of Converter-driven instability. The effects of damping and fault-ride through (FRT) make the transient dynamics more complicated. This paper introduces a combination of geometric and algebraic methods to estimate the Converter-driven stability region of GFL inverters. It is illustrated that the equivalent damping effect from the proportional control in a phase-locked loop (PLL) significantly enlarges the stability region, whereas the active current injection shrinks the stability region. The reactive current droop characteristic also has impacts on the stability region, especially with active current injection. The switch-over between the droop mode and constant current mode requires extra precaution in the calculation of the equilibrium points and critical fault clearing time.