Current Saturation Analysis and Anti-Windup Control Design of Grid-Forming Voltage Source Converter

Grid-Forming voltage source converter (VSC) connected to grid will occur current saturation (CS) under large disturbance due to its weak over-current ability. At present, some researches have pointed out that CS is more likely to lead to transient instability of VSC, which has been solved to a certain extent. However, there are very few studies on the VSC's recovery after grid fault occurring. In this paper, the phenomenon and reasons that grid-forming VSC encounter CS are explained. In particular, the static limit boundary conditions of VSC under unsaturated mode are given analytically in this paper, and then the conditions for VSC to recover to normal mode after CS are also analyzed. The theory shows that if VSC is saturated, it is difficult to recover to normal mode even if the grid has returned to normal. The saturated VSC working as an abnormal current source cannot output active power according to the control command, which is harmful to the stable operation of power grid. In order to deal with this problem, based on the conditions of VSC recovering from CS to normal mode, an anti-windup stability enhanced control is proposed. Simulations and hardware-in-the-loop experiments verify the validity of the CS analysis and the effectiveness of the proposed control scheme.