A Unified Method for Assessing Frequency Support Capability of Diverse Renewable Power Generation Units

The proliferation of renewable power generation units (RGUs) deteriorates the physical inertia of the system, making the evaluation of unit-level frequency support capability (FSC) and system-level frequency stability increasingly important. However, the prior-art approaches lack a standardized framework for FSC assessment, and the non-disclosure of RGU information by manufacturers exacerbates this challenge. To address these issues, this paper proposes a unified transfer function structure (UTFS) model and its parameter solving method based on impedance measurement, enabling a unified assessment of both the unit-level FSC and system-level frequency stability. The unit-level UTFS can be obtained through frequencydomain approaches, e.g., xy-impedance measurements. Moreover, the system-level UTFS can be acquired through the simple aggregation of unit-level UTFS. Without detailed models or postevent data, the proposed framework uniformly represents the FSC of various RGUs through three key indicators: effective inertia, damping, and primary frequency regulation (PFR). Furthermore, the proposed method analytically derives system frequency indicators: frequency nadir, rate of change of frequency (RoCoF), and steady-state frequency deviation. Numerical simulations and analysis of the operational data of a provincial power grid are provided to validate the proposed method.