Assessment Method of Harmonic Contribution Based on Covariance Characteristic

The power quality problems caused by harmonic pollution become increasingly significant with a large number of power electronic devices accessing to power system. The calculation of harmonic impedance is an essential condition for effective harmonic control. However, in instances where utility harmonic is not stable, conventional methods for estimating harmonic impedance will have significant deviations, potentially resulting in inaccurate assessments of the harmonic contributions from various harmonic sources. Therefore, this study proposes an innovative approach using modified independent random vectors method combined with complex least squares method aimed at reducing the estimation errors associated with utility harmonic impedance. Firstly, calculating the covariance characteristics of harmonic voltage and harmonic current at the point of common coupling (PCC). Subsequently, the complex least squares method is used to evaluate utility harmonic impedance. Compared with the conventional methods, the method proposed in this study is significantly less disturbed by harmonic fluctuation when evaluating the harmonic impedance. Simulation cases have demonstrated the validity and accuracy of the proposed method.