An Interpolation DFT Algorithm Based On 8-term Cosine Window And Applications In The Dielectric Loss Measurement

The dielectric loss angle tangent(tanδ) is one important part of online monitoring device. By measuring the phase angle difference between measurement capacitive device operating voltage and current flowing through the device can measure tanδ. Measurements of harmonic analysis method has more advantages compared to other methods, therefore it has been widely used.The dielectric loss measurement using the harmonic analysis is analysed in the paper. Using window interpolation algorithm to solve fence effect of DFT calculation of the signal measurement and the spectrum of the signal leakage, window function for several common characteristics were studied and compared, and it sums up the principle function of the selected window. This paper study in-depth interpolation correction calculation method for each corresponding window function, interpolation method was validated by an example of the effect of a variety of windowing.This paper propose the calculation method using 8-term cosine window interpolation DFT algorithm. A This paper first analyzes the spectrum characteristics of 5 to 8-term cosine window and their impact on windowed interpolation DFT algorithm accuracy, then analyzes the interpolation algorithm and coefficients on 8-term cosine window in detail. the cubic spline function is adopted to calculate the frequency and the harmonic amplitude modification coefficient, and calculating burden was reduced. Results show that, compared to other cosine window interpolation DFT algorithm, the interpolation DFT algorithm based on 8-term cosine window has the higher accuracy, and the results verify the effectiveness of the proposed algorithm and practical.Finally, This paper studies the application to the dielectric loss calculation error problem of 8-term cosine window interpolation DFT algorithms and 5-term cosine window DFT interpolation algorithm., using examples, simulink Simulation Platform capacitive device simulation models, generating corresponding voltage, and sampling by setting parameters to simulate different sampling procedures and different conditions. Deal with sequence generated respectively, using 8-term cosine window interpolation DFT algorithms and 5-term cosine window Rife-Vincent(I) and dielectric loss factor is calculated. By comparing the calculated results, which demonstrate that 8-term cosine window interpolation higher accuracy than 5-term cosine window Rife-Vincent(I) in the dielectric loss factor windowed interpolation FFT.