Stability Analysis and Improvement Mechanism of Grid‐Forming Converter Connected to a Low‐Impedance Grid

ABSTRACT This paper investigates the stability and improvement mechanisms of a grid‐forming (GFM) converter connected to a low‐impedance grid. Initially, a state‐space model of the GFM converter integrated into an AC grid is developed for stability analysis. Subsequently, a dynamic model of the GFM converter, derived from Newton’s theory of classical mechanics, is presented to characterise the damping and synchronising power components. The stability mechanism of the GFM converter is elucidated by analysing the evolution of damping and synchronising power components in relation to varying grid strengths or control bandwidths. It is observed that the primary cause of GFM converter instability stems from negative damping components, which are influenced by both external factors inherent to the low‐impedance grid and internal factors inherent to terminal voltage control (TVC). For the external factor, virtual impedance compensation control is proposed to mitigate the negative impacts induced by the low‐impedance grid. Moreover, for the internal factor, q ‐axis terminal voltage compensation control is proposed to decrease the negative impacts induced by TVC. Finally, time‐domain simulations and experiments are both conducted to corroborate the aforementioned results.