Indices for measurement of harmonic distortion in power systems according to IEC 61000-4-7 standard

Among harmonic distortion indices presented in International Electrotechnical Commission (IET) standard 61000-4-7, only group total harmonic distortion (THDG) can be used for interharmonic pollution analysis. However, existence of interharmonic components around of fundamental frequency may deteriorate accuracy of this index. To solve this problem, two virtual groups according to IEC standard are defined in this study. Then, two new distortion indices are proposed by using virtual groups in equation of THDG index. The new distortion indices are named as: group and subgroup total harmonic distortion and improved THDG. On the basis of various simulation tests and usage of different waveform decomposition methods, it is shown that proposed indices can better show the amount of waveform distortion caused by interharmonics in respect to IEC indices.