Frequency Support From Kinetic Energy of DFIG-Based Wind Turbines Considering Speed Limitation

Kinetic energy of DFIG-based wind turbines (WTs) can be released to provide frequency support for power systems, as the DFIG has a wide admissible range of rotor speed. In this paper, an adaptive frequency support (AFS) based speed control is proposed for DFIG-based WTs. In the case of grid frequency drop, the proposed control scheme can directly regulate the WT's rotor speed and release the kinetic energy for frequency support. Moreover, the rotor speed can be limited within the admissible range. Control design for the proposed scheme is elaborately presented. In addition, to analyze the WT's dynamic behavior, model reduction for the WT system is conducted, wherein the proposed control scheme is applied. The derived reduced-order model not only precisely replicates the dynamics of the full-order WT system, but also greatly relieves computation burden and thus enables simulations of large-scale wind farms. Based on the reduced-order model, a two-area test system, which contains three hundred DFIG-based WTs in three wind farms, is simulated. It's shown that the proposed control scheme can fully utilize the stored kinetic energy of large-scale wind farms for frequency support, which reduces frequency fluctuations greatly and thus improve the frequency stability of power systems.