Experimental Indicators of Current Unbalance in Building Integrated Photovoltaic Systems

Unbalance of the three-phase currents in photovoltaic (PV) systems may depend on structural aspects of the installation, the effect of partial shading, or both. In this paper, a number of unbalance indicators are calculated starting from data measured during experimental analyses on a real building-integrated PV system representing different types of unbalance. Detailed information is obtained from indices identifying the balance and unbalance components also in the presence of waveform distortion. These indices extend the current definitions of unbalance given in the power quality standards. The results show that the unbalance cannot be considered negligible even without single-phase inverters and is more significant if non-linear loads add a contribution to both harmonic distortion and unbalance seen from the distribution transformer.