Robustness testing of two impedance estimation techniques in weak grids

Abstract

Due to instability issues that arise in weak grids, knowledge of the grid impedance can improve the performance of converters connected to such networks. The existing method of active and reactive power variation is adapted to weak grid control, where the active power and voltage magnitude are varied instead. The impedance estimation is undertaken either algebraically using two sets of measurements at two different operating points, or using the recursive least squares technique with multiple measurements at multiple different operating points. It is demonstrated that the recursive least squares estimation technique yields the most reliable results for inductance estimation for various short circuit levels, network types and noise levels. The optimal variation of active power and voltage magnitude are identified for robustness against system variability. It is also shown that at transmission level X/R ratios, the estimation for resistance is poor.