用改进的DFT改进MOA容性电流补偿法

Modified Capacitive Current Compensation Method of MOA Using Improved DFT

为解决非整周期采样时改进的容性电流补偿法存在频谱泄漏和栅栏效应而影响算得的阻性电流准确性的问题,提出了基于加Blackman-Harris窗插值的改进容性电流补偿法,有效减轻了非整周期采样给阻性电流测量造成的误差。比较仿真模型给出的原算法和改进算法所得阻性电流基波和3次谐波分量的误差表明,新算法的误差仅为原算法的几分之一到几万分之一测量的准确大为提高。

The improved capacitive current compensation method considers and compensates capacitive harmonics current generated by voltage harmonics, so it has high accuracy in integer period sampling. In non-integer period sampling, due to spectral leakage and fence effect of improved capacitive current compensation method, the accuracy of measured resistive current of MOA （Metal Oxide Surge Attester） is influenced, and the accuracy of MOA fault diagnosis method based on fundamental harmonic and third-harmonic of resistive current decreases. For solving the problems, modified capacitive current compensation method based on the Blackman-Harris window and interpolation is proposed in this paper, the method uses the Blackman-Harris window to suppress spectral leakage and uses interpolation to decrease fence effect, so error of resistive current caused by non-integer period sampling decreases effectively. Fundamental harmonic and third-harmonic of resistive current of simulation model are calculated by the original method and the proposed method, and the results indicate that when the voltage has not harmonics, and signal frequency fluctuates from 49. 5Hz to 50. 5Hz, relative error of resistive current fundamental harmonic can reach 30%, and the relative error of resistive current third-harmonic excesses 130%. If the proposed algorithm is used, the relative error of resistive current third-harmonic is less than 2 %, the relative error of resistive current fundamental harmonic is even less. With the increase of voltage third-harmonic, errors of resistive current fundamental harmonic and third-harmonic will increase. When calculated by the original improved capacitive current compensation method, error of resistive current fundamental harmonic and third-harmonic approximate to 35 % and 200%, respectively, and the voltage third-harmonic is equal to 5 % of fundamental harmonic. However, by using the modified capacitive current compensation method proposed by the paper, the relative error of resistive current third-harmonic is always less than 2.5 %, that of fundamental harmonic is less, so the MOA fault diagnosis accuracy based on resistive current fundamental harmonic and third-harmonic will increase. Those results verify the effect of the proposed method.