信号幅值变化时的电力系统动态频率测量

Measurement of Power System Dynamic Frequency Under Signal Amplitude Variation

研究电力系统信号幅值变化对频率测量结果的影响,通过数学推导证明了当前各种测频算法所基于的信号幅值在一定时间间隔内不变的基本假设条件下测量的结果存在着误差。由此对传统频率定义进行扩展,提出了信号视在相角和视在频率概念,通过分析真实的瞬时频率与视在频率之间的差异,证明了信号幅值变化时,视在频率是信号真实频率与部分高频分量(约100 Hz及倍频)的迭加,残存的倍频分量需通过对实测频率进行低通滤波处理。通过具体仿真实例,验证了幅值变化的电网信号经低通滤波器的再处理后,能基本准确反映信号的实际瞬时频率。

This paper studies the effect of signal amplitude changes on the results of frequency measurement in power systems. Conventional frequency measurement approaches will cause measuring errors, which is proved by mathematic deduction based on the assumption that signal amplitude will keep constant during the given time interval. The concept of signal＇s apparent frequency and apparent phase is proposed based on the extension of traditional concept of frequency. The apparent frequency is the superposition of actual signal and some high frequency components （about 100 Hz） while signal amplitude is changing,which is proved by analyzing the difference between the actual instantaneous frequency and apparent frequency. Remained double-frequency component should be filtered by low-pass filter. Simulation result shows that the low-pass filtered signal can accurately reflect the actual instantaneous frequency.