Impact of Multiple Identical Grid-connected DFIGs on the Small-signal Angular Stability of Power System

It has been reported that a wind farm consisting of multiple identical or similar DFIGs may cause the small-signal angular instability of power system. In this paper, the phenomenon is studied from the perspective of Bode diagram. Firstly, the stability analysis method of Bode diagram derived from the Nyquist stability criterion and the self-oscillation theory are introduced respectively, which have similar conclusions. Subsequently, closed-loop interconnected model of multi-machine power system connected with multiple DFIGs is established. Impact of multiple identical grid-connected DFIGs on the small-signal angular stability of power system is studied via Bode diagram. The analysis shows that with the number of DFIGs increases, the phase curve of Bode diagram of the open-loop transfer function does not change, and the amplitude curve gradually shifts upward. According to the stability margin defined in the Bode diagram method, the stability of the closed-loop system decreases. Finally, the theoretical analysis is verified by two example power systems. The simulation results show that the instability of power system connected with multiple identical DFIGs can lead to small-signal angular instability in the power system.