A new method based on the threshold voltage is proposed to determine the main harmonic disturbance sources on the point of common coupling (PCC) in distribution systems. The threshold voltage can be calculated based on the system equivalent harmonic current sources and the equivalent impedances downstream and upstream of the PCC. The threshold voltage corresponds to the critical voltage value when the system and customer side issued the same amount of harmonic currents. The main harmonic sources on the PCC can be determined by comparing the measured PCC voltage and the calculated threshold voltage. The system parameter estimation method adopted makes it possible to avoid the bad impact of background harmonic variation

guaranteeing the good robustness of the method proposed

whose validity is verified by simulation and actual field data analysis. This work is supported by National Natural Science Foundation of China (No. 51107074)

Distinguished Young and Middle-aged Scientists Program Foundation of Shandong (No. BS2013NJ005)

and Program Foundation of China Scholarship Council (No. 20133018).