Research on Inertia Characteristics and Minimum Inertia Evaluation Method of Doubly-fed Wind Power System after Grid Connection

With the large-scale grid connection of wind power, its “zero inertia” feature reduces the grid inertia level and worsens the frequency characteristics. In order to find out the influence rule of wind power grid connection on the system inertia level and clarify the system operation boundary, the inertia characteristics and minimum inertia requirements of the wind power grid connection system are studied and evaluated. First of all, under different operation modes of synchronous generator, the calculation formula for evaluating the change of inertia characteristics of wind power grid-connected system is deduced theoretically, and the change law of inertia characteristics of the system is analyzed. In the case of wind power additional virtual inertia control, starting from the energy provided by the inertia response process, the average inertia support power is based on the system inertia weakening amount and the wind power virtual inertia, an inertia change coefficient COIC is defined to determine the system inertia level change. Secondly, an improved system frequency response(SFR) model considering wind power permeability is established to quantify the relationship between system inertia and wind power permeability, and the minimum inertia evaluation method of wind power grid-connected system is given. Finally, a four-machine two-region model with wind power access is built, and the theoretical analysis results and the proposed method are verified by simulation.