FAST AND ACCURATE METHOD TO MEASURE INTERHARMONICS IN POWER-SYSTEMS

In order to improve the resolution of spectrum analysis, the tradition al method is to take more sampling periods, e. g. 50 sampling periods corresponding to the spectrum interval of I Hz. This method is not sui table to the interharmonic measurement, because most interharmonics va ry rather quickly with the time and so the analysis results based on l ong time sampling may be useless. In this paper the zero-padding techn ique with short sampling time is used to resolve interharmonics, and t he zoom FFT is used to decrease the computation time in order to meet the needs of real-time measurement. The simulating computation shows t hat the resolution for two adjacent frequency components is usually su fficient to measure harmonics and interharmonics in power systems with acceptable short sampling and computation time. This method is also s uited to analyse harmonics and interharmonics when there exists an und esirable asynchronous deviation between the sampling period and the si gnal period.