Real-Time Grid Impedance Estimation Using a Converter

This paper presents two real-time methods for estimating the grid inductance and resistance using a three-phase converter. In the methods, a single-frequency rotating voltage signal with a small magnitude is injected to the converter voltage reference. The converter measures the currents and voltages at the point of common coupling (PCC). The grid impedance is estimated from the measured data using two alternative methods: an estimator based on the sliding discrete Fourier transform (SDFT) and an adaptive grid observer. Dynamic performance of these methods is compared by means of simulations and experiments in the case of a changing grid impedance.