Harmonic interaction of electric vehicle chargers in a central charging infrastructure

The operation of electric vehicles (EVs) in a central charging infrastructure represents an important future scenario for network operators. As EV chargers contain power electronics, such a scenario needs to be evaluated also with regard to Power Quality (PQ), in particular harmonics. Therefore, a field study has been carried out in a low voltage (LV) network with mainly commercial users and five three-phase EVs connected to one terminal. A large heat pump and some further loads were connected to the same terminal, which allows an assessment of the total harmonic emission for different combinations of the above mentioned devices. The emission of the combined operation is characterized by different cancellation effects between all devices as well as by the mutual influence between the voltage distortion and the harmonic currents. Particularly, the heat pump strongly influences the existing voltage distortion, which in turn affects the harmonic current emission of the EVs. To explain these harmonic interactions, the concept of primary and secondary cancellation is applied. The results of this field study are finally used for the validation of existing harmonic EV models. A comparison between measured and simulated harmonic currents has shown a good match.