Interharmonics: basic concepts and techniques for their detection and measurement

The term interharmonics refer to those frequencies that are not integral harmonics of the supply fundamental frequency. Although international organizations defined the terminology and proposed measurement guidelines, difficulties still exist in its detection and measurement with acceptable accuracy. When interharmonic components appear in a spectrum, it is still debatable if they really exist and, if the answer is yes, what are the actual frequencies and magnitudes of the components. This paper reviews the mathematical basis of the interharmonics and discusses the difficulties in detecting and measuring interharmonics. A few practical rules are proposed to assist the measurement of interharmonics. Simulations, laboratory experiment and field test results are provided to illustrate the difficulties in interharmonics analysis. (C) 2003 Elsevier Science B.V. All rights reserved.