Research on Control Strategy of Participating in Frequency Regulation for the System of DFIG-Based Wind Farm Connected to the Grid via Fractional Frequency Transmission System

Fractional frequency transmission., as a new type of wind power grid-connection method., is suitable for large-capacity and long-distance transmission of electric power. However., the access of large-scale wind power will lead to the reduction of power system inertia and frequency stability. For the fractional-frequency doubly-fed wind power system., this paper utilizes the static electric energy stored in the capacitance of the modular multi-level matrix converter (M3C) submodule., as well as the kinetic energy and spare power in the wind turbine., to design the M3C virtual inertia control strategy., the doubly-fed wind turbine frequency control strategy and the joint frequency control strategy. The corresponding simulation model is established in the PSCAD/EMTDC. And the simulation results show that the proposed control strategy can improve the nadir frequency (NF) of once-drop., slows down the rate of change of frequency (RoCoF)., and effectively enhances the stability of the industrial frequency (IF) system.