Adaptive Temporary Frequency Support for DFIG-Based Wind Turbines

For a doubly-fed induction generator (DFIG)-based wind turbine (WT), the temporary frequency support (TFS) is a cost-effective strategy to achieve the system frequency regulation capability. However, there is no coupling relationship between the power increment and the system frequency in the existing TFS strategies, which limits the frequency support capability of WTs and even deteriorates the system frequency. To cope with it, this paper analyzes the adaptability of two representative TFS strategies under different load disturbance scenarios, and proposes some design guidelines for the power trajectory. Subsequently, an adaptive temporary frequency support (ATFS) strategy is proposed to improve the frequency stability when faced with different load disturbances. In the method, the initial power reference varies with the initial rate of change of frequency, and the power reference is reduced along the upward parabola and semicircle in the frequency support stage and rotor speed recovery stage, respectively. Furthermore, the ATFS strategy can improve the frequency nadir adaptively while well balancing the secondary frequency dip (SFD) and the speed recovery in different scenarios. Finally, the ATFS strategy is verified by hardware-in-loop (HIL) simulations.