Analysis of PLL Parameters' influence on the Stability of DFIG System under Weak Grid Conditions and its Active Configuration

In modern power systems with high penetration rates of renewable energy, its grids impedance cannot be ignored and varies dramatically in response to the changes of grid operation mode. The doubly-fed induction generator (DFIG) connected to this type of weak grid easily suffers from stability and performance problems. This is due to the increased interaction between the traditional phase-locked loop (PLL) and the weak grid. However, in practical applications, the control parameters of the traditional PLL are usually constant parameters designed under strong grid conditions, which greatly hinders the grid adaptability of DFIG and affects the stability of DFIG in weak grids. In order to reveal the interaction mechanism between the PLL and the weak grid, this paper focuses on the influence of the PLL bandwidth parameter on the impedance characteristics of the DFIG based on the sequence impedance model of DFIG system considering PLL. Then the safe and stable operating area of DFIG is obtained and deduced. Based on this, an adaptive PLL parameter control strategy is proposed. Finally, time-domain simulation (MATLAB / Simulink) verifies the validity of the theoretical analysis.