Measurement method of harmonics and inter-harmonics with nonsynchronous sampling in IEC framework

This paper focus on harmonics and inter-harmonics with nonsynchronous sampling in IEC 61000-4-7 standard framework measurement problem, proposed the group measurement method and accurate measurement method of harmonics and inter-harmonics, and through removing the leakage value of other components on the concerned lines to eliminate interference of other components, solved the problem of adjacent harmonics and inter-harmonics parameters accurate separation. DFT/FFT spectrum leakage occurred when nonsynchronous sampling in fundamental frequency, harmonics and inter-harmonics spectrum mutual interference affect the measurement results, the traditional interpolating windowed FFT method ignores the long-range leakage which came from other components on the concerned component. Firstly, the paper transformed the spectrum of Hanning weighted signal in IEC framework with nonsynchronous sampling, and adjusted the phase factor of spectrum, to change side lobes adjacent spectral phase difference of 180 degrees in other components, used the vector sum of adjacent lines to eliminate the long-range leakage on the concerned component, thereby proposed the group measurement method and accurate measurement method of harmonics and inter-harmonics, achieving harmonics and inter-harmonics specific parameters measurement. Based on that, proposed the harmonics and inter-harmonics separated method, and further successive removed the leakage value of other components on the concerned lines to improve the measurement accuracy, when nonsynchronous sampling without increasing the length of the sampling data, an effective solution to the harmonics and inter-harmonics cannot be accurately measured when closely spaced separation problem. Through the simulation of 10 cycles nonsynchronous sampling data, with other components and noise interferences, achieved a separation measure of 150.3Hz harmonics and adjacent 152.1Hz inter-harmonics under 5Hz frequency resolution, the relative errors are les- than 0.01%, and validated real-time and effective characteristics of the proposed methods in IEC framework.