基于锁相环同步控制的双馈风机弱电网接入稳定性分析

Phase-locked loop (PLL) is commonly used in doubly-fed induction generator (DFIG) for its grid synchronization by tracking the phase angle of turbine terminal voltage; however a DFIG which is connected to weak grids by a synchronization technique will lead to instability. Consequently, we try to uncover the mechanism of phenomenon of instability. In non-ideal grid connection, terminal voltage phase angel is affected by the power outputs of DFIG, resulting in a dynamic coupling between PLL and DFIG power controls. Considering such a coupling effect, we propose a reduced small-signal model for a single DFIG infinite bus system. Based on this model, it is found that, owing to the coupling relation within active power and terminal voltage magnitude, an addition positive feedback branch is introduced to the PLL, and the loop gain increases as the system strength decreases, thus the stability of DFIG under weak grid operating conditions is deteriorated. Moreover, for open-loop terminal voltage control condition, the stability margin is analytically derived. Furthermore, the impact of terminal voltage control is also qualitatively analyzed. Full-order time-domain simulations are conducted to verify the effectiveness of the proposed simplified model and correlated analysis.