An improved grid impedance estimator for grid-forming converters in consideration of controller dynamics

Abstract

Equivalent grid impedance is an essential parameter in the stability analysis of grid-forming converters. The grid impedance estimator based on the PQ variations technique is popular in practice, yet this technique has limited estimation accuracy and dynamics. To address this issue, the effect of phase error on grid impedance estimation during power variations is demonstrated in this paper. The phase error is quantitatively described by investigating the impact of controller dynamics on the equivalent grid impedance model. By compensating for the phase error, an improved grid impedance estimator with only the active power disturbance is proposed, and its implementation and tuning are discussed. Compared with the conventional estimators, the proposed grid impedance estimator is of high estimation accuracy and speed with less disturbance. Simulation and experimental results validate the effectiveness and simplicity of the improved grid impedance estimator.