A Method for Estimating the Utility Harmonic Impedance Based on Semiparametric Estimation

Abstract

Estimating the utility harmonic impedance of a point of common coupling (PCC) is of significance to harmonic emission level evaluation. The most existing methods for estimating the utility harmonic impedance are based on the assumptions that the background harmonic fluctuates in a small range, and the customer harmonic impedance is much larger than the utility harmonic impedance, etc. However, in modern power grid, due to the influence of filter and reactive power compensator, those assumptions are not always satisfied. Just depending on the stochastic characteristic of the utility harmonic current, this article proposes a method for estimating the utility harmonic impedance based on semiparametric estimation. The input of the proposed method is the measured voltage and current at the PCC. The kernel density estimation method, one of the nonparametric methods, is used to depict the probability distribution characteristics of the utility harmonic current, and the impedance is obtained according to maximum likelihood estimation (MLE) criterion. The performance of the proposed method is verified by simulation experiments and field-measured data. The results validate that the proposed method outperforms the existing methods when the background harmonic is fluctuating and the utility harmonic impedance is close to the customer harmonic impedance.