Evaluation of wind power plants' control capabilities to provide primary frequency support during system restoration

Abstract

This paper investigates the utilization of wind power plant (WPP) controllers to support the frequency of an island grid during the early stages of a grid restoration (GR) process. It was found that the frequency support provided by the WPP can be augmented through the adjustment of the controllers' parameters. Time domain simulations were employed to quantify the effect and to evaluate the stability of the system. By using a farm controller with integrated <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$P(f)$</tex> -curve, the WPP can be operated and throttled by grid operator on demand, feeding additional power in case of frequency declines. The frequency nadir following a reconnection of load can thus be mitigated and the restoration process can be sped up in this way. By adjusting the slope as well as the controller parameters, the effect can be amplified. However, the wrong selection of the new parameters can lead to an unstable system. The creation of a simplified, linearized model of the complete system allows an eigenvalue analysis in the frequency domain for systematic stability evaluation, and for the design of the controller parameters. Damping is neglected, which is why the stability is evaluated more critically using the eigenvalue analysis than the simulations in the time domain.