Comparison of Transient Frequency Estimation Methods for Evaluating the Frequency Gradient in Active Distribution Grids

In the interconnected power system, frequency control and stability are of vital importance and an indicator of the system-wide active power balance. The shutdown of conventional power plants leads to faster frequency changes and a steeper frequency gradient due to the reduced system inertia. For this reason, the importance of electrical frequency estimation methods is increasing, among others as an input variable for the control of converter-based generation plants. The aim of this work is to implement, compare and analyze the robustness of different frequency estimation methods in time-domain simulations. The Phase-Locked Loop, the Zero-Crossing method and the Recursive-Gauss-Newton method are implemented as real-time methods in a simple testbench in Matlab/Simulink. The parameters of the methods are tuned for a reference case and compared to the rotational frequency of a connected synchronous generator. With the tuned parameters, the maximum deviation between frequency estimation and the synchronous generator frequency can be limited to 15 mHz. The Zero-Crossing method shows the best robustness when changing the magnitude of the active power imbalance. In addition, the sensitive parameters of the frequency estimation methods behave approximately linear to the magnitude of the active power imbalance, so that a simple implementation can be designed for simulations.