Continuous harmonic impedance assessment using online measurements

Abstract

The quantification of harmonic emission requires an accurate representation of the network harmonic impedances. A number of techniques have been proposed to make the assessment of the network harmonic impedances practical and less invasive. Using actual event data, captured at a solar farm, this paper aims to utilize existing assessment techniques to develop an online network harmonic impedances assessment model. The harmonic impedances can then be updated per event and automatically be corrected as the network develops. This technique is noninvasive and will provide an accurate estimation of the network impedances enabling the continuous assessment of power quality emissions

Review of Local Network Impedance Estimation Techniques

“…Reference [67] identifies that a sufficiently large grid event has occurred when a 3% change in RMS voltage is registered. The transients caused by such an event can provide information about the system across a wide range of frequencies.…”

“…Notice that (10) is similar to (8), with the difference being that (8) is valid for the fundamental frequency impedance only (the Thévenin equivalent), whereas (10) can determine the impedance at a range of frequencies, subject to the FFT implementation. With the observer implementation described in [67], good estimations require data accumulated by 70 grid events over 15 days -the accuracy of the estimates are not explicitly stated, but this is clear in the article figures. In [68], the same authors presented the same data with the addition of the reference impedance value.…”

Study on the Estimation of Utility Harmonic Impedance Based on Minimum Norm of Impedance Difference

“…The existing noninvasive methods include: the fluctuation methods [15]- [17], the regression methods [18]- [22], the method based on covariance characteristic of random vectors [23], ICA methods [11], [24], [25], and other methods [26]- [30]. The fluctuation methods and regression methods can get accurate results with the preconditions, that is background harmonic is stable and customer harmonic impedance is much larger than that of the utility side.…”

Network resonance detection using harmonic active power

“…In situ monitoring of those impedance over frequency plots is essential for stable operation, but this generally requires intrusive methods. There have been some suggestions of algorithms to try to obtain this data based on measurements using non-intrusive techniques [4], [5]. This proves to be promising, although the long iterative process requires a lot of time.…”