The analysis of output voltage distortion of inverter for frequency lower than the nominal

Abstract

The paper discussed the studies related to the output voltage distortion of frequency inverter depending on its frequency. The changes in the effective value of voltage, THD, harmonics and interharmonics were presented for three different frequencies, lower than 50Hz. Additionally, it was shown how these values change depending on measurement time, presenting waveforms cycle by cycle in graphs, averaged in 10 periods and averaged in 150 periods of the analyzed signal. The studies were conducted in the laboratory area equipped with power quality meter class A.

The Influence of Measurement Methodology on the Accuracy of Electrical Waveform Distortion Analysis

“…In order to gain the accurate assessment of the electrical waveform distortion, the distortion components have to be representative and integral to reality. The authors of numerous works [6], [8], [23], [24], [25], [26] indicate that restriction of the spectrum suggested in the norm [10] to 50 components may be the reason for the discrepancies. In work [23] presents the practical example of the supply voltage on a ship.…”

“…It was probably caused, among others, by a reduced range of analyzed spectrum, according to the norm [10]. Further studies [6], [26] indicated that narrowing the spectrum of harmonics may affect other parameters that describe electrical waveforms such as effective value (RMS), waveform distortion factor (THD), and crest factor (CF).…”

“…Periodical waveforms are very often involved when voltage and current waveforms are distorted as a result of non-linear machine work. However, when waveform distortion is the result of the work of electrical switching components, the signal is very often unsteady [5], [6] and has components of frequency from several hundreds of Hz to several tens of kHz, that are not synchronized with the network. This type of signals is not easy to measure and analyze as they comprise both harmonics and interharmonics, slow changing components and fast changing components that additionally can change over time.…”