Virtual-Admittance Control Method for Stability Improvement of Type III Wind Turbines in Power Networks With High-Frequency Resonances

Abstract

Renewable power plants are prone to high-frequency resonances that threaten the stability of their generators. In this regard, the design of supplementary controllers for shaping the output impedance and improving the stability margins is of great interest, although it requires a detailed design procedure. In this work, two formulations for a virtual admittance control aimed at improving the stability margins of type III wind turbines in applications involving high-frequency resonances are presented. The first one is based on explicit formulas and guarantees a resistive behaviour of the wind turbine at a given frequency, while the second relies on the vector-fitting algorithm to extend the application to a given frequency range. The proposed controllers are designed based on impedance models, so there is no need for analytical models of the wind turbine nor the grid. The main contributions are validated by using a numerical simulation performed in MATLAB/Simulink and a real-time simulation executed on an OPAL-RT platform. The results show that the single-frequency compensation method is simpler to implement, but the stability margins are degraded when the resonance frequency of the grid changes. In contrast, with the multi-frequency compensator, the stability margins remain sizeable even if the resonance frequency changes, at the expense of a more complex implementation.