应用于频率宽范围偏移电网的改进相位差校正法

非同步采样造成的频谱泄漏是相位差测量误差的主要来源,尤其针对于频率宽范围偏移时,采用传统相位差法很可能造成测量失败。文中提出一种基于传统相位差的改进算法,改进算法分为两个步骤:第一,通过分析加窗信号频谱,将频谱表达式进行多项式变换从而加快旁瓣衰减速度,进一步减轻频谱泄漏和各谱线之间的干扰;第二,通过估计电网基波频率偏移范围确定待测信号采样点数,对采样序列采用截取点数不同的前后两次相位差法,第二次相位差法的截取点数由第一次相位差法估计的基波频率决定,减小了非同步采样带来的频谱泄漏。分别在基波频率稳定、基波频率宽范围偏移以及含有噪声干扰的情况下进行仿真验证。仿真结果表明,改进算法的电参数测量精度较传统相位差法有大幅度的提升,采样窗长满足IEC标准规定窗长。

Improved Phase Difference Correction Method Applied in Power Systems with Wide Frequency Offset Range

The spectral leakage caused by non-synchronous sampling is the main error source of phase difference measurement. In particular, for the wide range of frequency offset, the conventional phase difference method may make the measurement fail. This paper proposes an improved algorithm based on the conventional phase difference method. The improved algorithm is divided into two steps. Firstly, by analyzing the signal spectrum of the windowing, the polynomial transformation of spectral expression is conducted to speed up the sidelobes decay and further reduce the spectral leakage and the interference between the lines. Secondly, the number of sampling points of the signal to be measured is obtained by estimating the frequency offset range of the fundamental frequency of the grid, and two phase difference methods with different numbers of intercept points in the sampling sequence are employed. The number of intercept points of the second phase difference method is estimated by the fundamental frequency of the first phase difference method, to reduce the spectral leakage caused by the non-synchronous sampling. The simulation is conducted in scenarios of fundamental frequency stability, wide frequency offset range and interference with noise. The simulation results show that the measurement accuracy of the improved electrical parameters is much higher than that of the conventional phase difference method, and the sampling window length satisfies the IEC standard.