Recovery time and strategy of DFIG speed based on a high-proportional hydropower grid

Abstract

Large-scale wind power access reduces the equivalent inertia of a power system. The wind turbine has a considerable reserve of rotational inertia, which is important for reducing the risk of low-inertia operation in a grid and for improving frequency reliability. In this work, a doubly fed induction generator (DFIG) inertia frequency regulation strategy is studied. The secondary dip in frequency caused by speed recovery after the wind turbine participates in frequency regulation is an important factor that limits regulation capability on the DFIG. To address such problem, the power dip and recovery generated by the DFIG after active speed recovery is analyzed and modeled. Then, a linearized frequency response model of a hydropower single machine is established to investigate the secondary disturbance effect of wind turbine active speed recovery moment on the frequency of the high-ratio hydropower system.A conclusion is drawn that the moment that corresponds to the first recovery of system frequency to the quasi-steady-state frequency is the optimal recovery moment of the turbine in the linear SFR model. Combined with the frequency control characteristics of the frequency limit control(FLC)’s “large dead zone, ” an active speed recovery strategy of the turbine based on frequency deviation judgment is designed.