The harmonic and interharmonic analysis recommendations are contained in\nthe latest IEC standards on power quality. Measurement and analysis experiences\nhave shown that great difficulties arise in the interharmonic detection and measurement\nwith acceptable levels of accuracy. In order to improve the resolution\nof spectrum analysis, the traditional method (e.g. discrete Fourier transform)\nis to take more sampling cycles, e.g. 10 sampling cycles corresponding to\nthe spectrum interval of 5 Hz while the fundamental frequency is 50 Hz. However,\nthis method is not suitable to the interharmonic measurement, because\nthe frequencies of interharmonic components are non-integer multiples of the\nfundamental frequency, which makes the measurement additionally difficult.\nIn this paper, the tunable resolution multiple signal classification (TRMUSIC)\nalgorithm is presented, which the spectrum can be tuned to exhibit high resolution\nin targeted regions. Some simulation examples show that the resolution\nfor two adjacent frequency components is usually sufficient to measure interharmonics\nin power systems with acceptable computation time. The proposed\nmethod is also suited to analyze interharmonics when there exists an undesirable\nasynchronous deviation and additive white noise.
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