Harmonic impedance estimation considering the correlation between harmonic sources☆

Abstract

The previous utility harmonic impedance estimation methods are usually based on the assumption that harmonic sources are independent, which will cause large errors when the assumption is not met. To solve this problem, a method to weaken the negative effect of the correlation to impedance estimation is proposed. In the proposed method, the correlation between harmonic sources is reflected by that between constructed background harmonic voltage and measured harmonic current, and the effect of correlation is suppressed by obtaining the weak correlation time interval. First, construct the background harmonic voltage data based on the initial impedance, which changes in the range set according to the value of system short-circuit capacity. And then sort and divide these data into several sub-segments. Further, apply the correlation function to calculate impedance with each sub-segment. Finally, select the optimal impedance from all the initial impedances by comparing the difference between the calculated impedance and the initial impedance. The proposed method is more accurate when the correlation between harmonic sources is strong compared to other methods. Meanwhile, the processing of the background harmonic makes this method resist the significant background harmonic fluctuations. The effectiveness of the method is verified by simulation and field cases