Assessing Utility Harmonic Impedance Based on the Covariance Characteristic of Random Vectors

This paper presents a new method to calculate the utility harmonic impedance and the harmonic voltage emission level at the point of common coupling (PCC). Since harmonic current at the PCC commonly exhibits negligible dependence on the utility side background harmonic, the variable item of the background harmonic in the deviation formulation can be eliminated by using the covariance characteristic of random vectors. And then, the utility harmonic impedance, the customer harmonic voltage emission level, and the background harmonic can be calculated in real time. Based on the analysis results of the simulation and the field test case, it shows that the proposed method is effective to reduce the calculation errors caused by the fluctuation of background harmonic, and satisfactory results can be achieved.