Real-Time Grid Impedance Estimation Using a Converter

Abstract

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.

An Approach Utilizing Converters for Locating Faults in LV Distribution Grids

“…In this paper, the grid-impedance estimators of the converters are based on sliding discrete Fourier transform and they are implemented as in [27]. A block diagram of the converter control system with the impedance estimation method is presented in Fig.…”

“…Since the amplitude of the injected signal is very low compared to that of the grid voltage and the injection frequency is chosen to be outside of the grid harmonics, the effect of the injection signal on other components in the grid be considered negligible. More detailed description of the estimation method can be found in [27].…”

Review of Local Network Impedance Estimation Techniques

“…[83], [84] excites at 400 and 600 Hz, except that in [84] voltage is excited instead of the current. Interestingly, [85] excites a frequency of 10 Hz. Of the implementations discussed in this section, only [83]- [85] calculated both resistance and reactance as separate parameters -all other implementations only calculated the impedance magnitude.…”

“…Interestingly, [85] excites a frequency of 10 Hz. Of the implementations discussed in this section, only [83]- [85] calculated both resistance and reactance as separate parameters -all other implementations only calculated the impedance magnitude. Nonharmonic perturbations can be injected in the dq-frame as per Fig.…”

Estimation of an Unbalanced Grid Impedance Using a Three-Phase Power Converter

“…In the SDFT module, the resonator coefficient c e = exp(−jω e T s ) selects the frequency of the single DFT bin for the phasor calculation as explained in [19]. It is to be noted that, ω e has to be integer multiple of the angular frequency resolution of the SDFT module as in the case of the conventional DFT.…”