考虑电网频率变化率的改进相位差校正法研究

针对电网信号基波频率动态变化时相位差校正法测量结果存在较大误差,甚至可能测量失败的问题,提出了一种考虑频率变化率的改进相位差校正法。指出了非同步采样造成的频谱泄漏是相位差校正法测量误差的主要来源,尤其当基频动态变化导致基波频率偏移较大时,非同步采样使测量精度严重降低。推导了基于频率变化率修正的归一化频率校正量公式,在线测量时,频率变化率用前次与当次测得的基波频率进行差商运算求得,再据此对测量结果进行了修正。分别使用考虑频率变化率的方法和原方法对变频电网信号进行了数值仿真研究。研究结果表明,改进相位差校正法有更高的测量精度,对基波的测量精度提高一个数量级,采样窗长为IEC标准规定窗长的50%,能满足频率动态变化时谐波在线测量的精度与实时性要求。

An improved phase difference correction method considering rate of change of frequency of the power systems

Aiming at the problem that the phase difference correction method had a large error and sometimes might fail when the fundamental frequencies of the power signals varied with time,an improved phase difference correction method considering the rate of change of frequency (ROCOF) was presented.The fact that the spectral leakage from asynchronous sampling was the main source of the measurement error for phase difference correction method in power harmonic analysis was pointed out.When the fundamental frequencies of the power signals varied with time which led to a remarkable frequency offset,the accuracy of the phase difference correction method was low because of the asynchronous sampling.The modified normalized frequency correction value based on the ROCOF was deduced.During online measurement,the rate of change of frequency was estimated by calculating the difference quotient of fundamental frequency of last measurement and this measurement.After that,the result of this measurement was modified with the ROCOF.The variable-frequency power signals were simulated using the method considering ROCOF and the original method respectively.The results indicate that the accuracy of the phase difference correction method considering ROCOF is higher than the original method.The accuracy of amplitudes is improved by one order of magnitude and the time length of the window is 50％ of that prescribed by IEC standard.This method satisfies the requirements of accuracy and real-time performance in the online harmonic measurements of the variable-frequency power systems.