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 that are measured during experimental analyses on a real building-integrated PV system that represents different types of unbalance. Detailed information is obtained from indices that identify the balance and unbalance components that are 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 with no single-phase inverters and is more significant if nonlinear loads add a contribution to both harmonic distortion and unbalance seen from the distribution transformer.