A Precise and Adaptive Algorithm for Interharmonics Measurement Based on Iterative DFT

A precise and adaptive algorithm for interharmonics detection based on iterative discrete Fourier transform (DFT) is proposed. First, an objective function is defined as the squared error between the transform of the signal in rectangular window based on kernel function, and the Fourier transform of the signal in infinite time domain. Then, the kernel function is obtained by solving the differential equation which minimizes the objective function. On this basis, the transform of the signal in rectangular window based on kernel function is obtained. Moreover, practical formulas to calculate the parameters of harmonics and interharmonics in electric power systems are presented. The proposed method has three distinguished features, first, it is able to measure interharmonics in time because the sampling time is only six periods of fundamental wave, second, it is not affected by asynchronous sampling, and third, it is only slightly affected by white noise. In addition, the frequency resolution can be adjusted adaptively by changing the number of frequency points. Some simulation examples are given to demonstrate the precision, effectiveness, feasibility, and robustness of iterative DFT algorithm.