In practical system, background harmonic impedance often changes owing to switching loads, and the present researches on the harmonic contributions determination based on constant background harmonic impedance are not applicable in this case. The paper studies the determination of harmonic contributions on condition of changing background harmonic impedance. The slope comparison method, which uses the relationship of harmonic voltage and harmonic current, is proposed to segment the sample data adaptively. In the same segment, geometric mean regression is adopted to estimate the background harmonic impedance accurately. Thus the segmental harmonic contributions are determined. Additionally, a total harmonic contribution index is established to effectively measure the harmonic contribution of customer. Simulations are carried on the simple Norton-equivalent circuit to validate the proposed method, and the proposed method is compared with traditional methods, which prove the effectiveness and accuracy of the method.
