Multi-layer coordinated frequency control strategy for WTGs and energy storage considering system inertia requirement

Abstract

Given the intimate correlation between the inertia response ability of wind turbine generators (WTGs) and their operational statuses, it becomes imperative to analyze the inertia contribution from wind farms across varying wind speeds and establish the rate of change of frequency (RoCoF) security boundary. Such endeavors are crucial for grid operators to assess the system's ability to withstand disturbances. This paper proposes a multi-layer frequency control method for hybrid wind power and energy storage (ES) systems. All WTGs and ESs in the wind farm are divided into several clusters. At the wind farm layer, the wind farm control center quantitatively assesses the maximum inertia that the wind farm can provide based on real-time wind speed and the operational status of WTGs, and communicates this information to the grid control center. At the grid layer, the power system operators establish the security boundary related to the RoCoF based on the inertia level of the wind farm and synchronous generators, thereby continuously evaluating the system's ability to withstand disturbances in real-time. In the event of significant disturbances (N-1 event), the power system dispatch center issues instructions to the wind farm, specifying the required level of inertia to be provided. The wind farm, in turn, coordinates the allocation of inertia among WTGs and ESs based on the dispatch center's instructions and considers the operational status of different WTGs, while tracking the system control commands. Through this approach, the inertia response ability of different WTGs and ESs can be fully utilized to enhance the transient frequency characteristics of the grid.