The Study On Measurement Of Interharmonics In Power Systems

With the rapid development of power electronics technology and the widely use of all kinds of power electronics instruments, the harm brought by interharmonics have attracted people's attention more and more. Current research shows that interharmonics voltage should be restrained to a low enough level.When we use FFT to analyze harmonics and interharmonics, the interharmonics component will result in a phenomenon of frequency spectrum leakage and make the amplitude-frequency image distorted, so we must judge the component of harmonics and interharmonics. On the other hand, the interharmonics are always various, so it is not fit to adopt short sampling time. This paper aims at studying a measuring method of interharmonics to estimate their parameters (frequency, amplitude, and initial phase angle) with the short-time sampling to the signal.This paper is based on the Fourier transform, whose sampling interval is adopted as 10 times of line-period while the power frequency is 50Hz. This paper simplifies the Fourier transform expression by some mathematical ways, proves the feasibility of simplification, analyzes the amplitude-frequency curve in the case of adopting the sampling interval as 10 power period, and draws the picture by employing MATLAB tools. With the FFT data and the Fourier transform simplified expression, the frequency, amplitude and the initial phase angle of inteharmonics are calculated. The results show that the errors meet with the request to precision.