A Method to Improve the Interharmonic Grouping Scheme Adopted by IEC Standard 61000-4-7

The interharmonic group concept adopted by the IEC 61000-4-7 is very useful for addressing the need to monitor interharmonics in power systems. This paper shows that grouping spectral bins into interharmonics and harmonic components of 5 Hz resolution could yield misleading information for cases where an interharmonic component´s frequency is very close to a harmonic frequency. Since interharmonics in such cases can cause more severe waveform modulation, the interharmonic grouping scheme needs to be improved. A signal-processing method that can separate interharmonic and harmonic components in close proximity is, therefore, proposed in this paper to address this need. The method is based on the estimation of leakage values caused by interharmonics, at harmonic frequencies. Simulation studies and field data analysis showed that the proposed method was able to extract interharmonic and harmonic components correctly. Moreover, this paper also discusses how to apply the method to enhance the spectral grouping scheme of the IEC 610004-7.