频率偏移时基波幅值计算误差对保护的影响及其改进算法

Effects of the Fundamental Amplitude's Calculational Errors when Frequency Offset on Protections and Its Improved Algorithm

分析了频率偏移时傅里叶算法计算的基波幅值的误差;分析了该误差对使用基波幅值作为动作量的过量保护和欠量保护的影响。通过分析得出傅里叶算法计算的基波幅值是频率为模拟量频率两倍的周期函数,在此基础上提出了一种频率偏移时基波幅值的改进算法,该算法通过把傅里叶算法计算出来的基波幅值在一个周期内求平均值再乘以一个与频率相关的系数来求取实际的基波幅值。MATLAB仿真和装置实测结果显示,所提出的改进算法计算的基波幅值误差很小,能够满足继电保护装置对模拟量精度的要求。

In this paper, analyses of the fundamental amplitude errors calculated by DFT when frequency offsets and effects of the errors on over protections and less protections which use the fundamental amplitude as action values are conducted. The facts that fundamental amplitude calculated by DFT is a periodic function and its period is twice of the input signal can be found. Hence an improved algorithm to calculate the fundamental amplitude when frequency offsets is putted forward based on the above facts, which calculates the fundamental amplitude by the product of the average value of the fundamental amplitudes calculated by DFT in one cycle and a coefficient related to the frequency. MATLAB simulation and test on practical device shows that, the errors of fundamental amplitude calculated by the improved algorithm when frequency offsets are very small, thus the errors can meet the requirements of the analog accuracy for power relay equipments.