Influence of Harmonic System Voltages on the Harmonic Current Emission of Photovoltaic Inverters

Harmonic currents of photovoltaic (PV)-inverters show a significant dependency on the harmonic voltage content of the alternating current (AC)-system voltage. Measurements of harmonic currents were carried out in low-voltage (LV)-systems and under laboratory test conditions with adjustable harmonic content of the AC-voltage. Two PV-inverters, one with coupling transformer and one without transformer were tested. The results indicated that the emitted harmonic currents depend strongly on the harmonic voltages prevailing in the AC-voltage. PV-inverters without transformer show significant lower harmonic currents than inverters with coupling transformer. The standard test conditions as defined in international standards does not consider real system conditions with respect to the harmonic voltages in system voltage. The measured currents as documented in data sheets are therefore comparatively lower than under the condition of real system operation.