Robustness testing of two impedance estimation techniques

In weak grids, a combination of high variability and low short circuit ratio forces converters to operate in the nonlinear region. In such situations, good converter control tuning is critical as poor tuning may lead to instability. One solution is to tune converters online, with the help of impedance estimators. Whilst impedance estimators have been proposed in the past, their performance in weak grids remains unclear. The aim of this paper is to compare two estimation methods by simulating them in a variety of weak grid scenarios. The estimators tested in this paper are the algebraic estimator and the recursive least squares estimator. These estimators are tested under various power and voltage magnitude deviations, in order to determine the optimum deviations for each method. The two methods are also directly compared, and it is determined that the recursive least squares estimator is more reliable and robust for different grid layouts, Thevenin equivalent impedance, and noise levels.