Multi-SIN Based Real-Time Impedance Estimation for Grid-Tied VSI

The paper proposes a new stimulus for online active and parametric estimation of resistive-inductive grid impedance using a grid-connected inverter. The proposed stimulus is designed with the goal of minimizing invasiveness on the grid, minimizing the time required for estimation, thus minimizing computational calculations, and ultimately optimizing the result. The initial estimation provides only the total impedance using the Fourier transform. To derive parameter values for resistance and inductance, a cyclical algorithm is performed that integrates the estimated impedance points as a function of frequency. Furthermore, a comparative analysis was conducted with other stimuli present in the literature. The comparison primarily focuses on the introduced total harmonic content and the distribution of harmonics across the spectrum frequency. To validate the estimation results and show the comparison with other stimuli, Hardware-in-The-Loop (HIL) tests were performed.