Harmonic distortion and unbalance analysis in multi-inverter photovoltaic systems

The growing penetration of distributed generation connected to the grid by power electronics converters can adversely affect the power quality. The capability of the system to host large harmonic distortions and unbalance in three-phase systems may be an issue. In case of Photovoltaic (PV) systems, the harmonic injection and unbalance are due to the transistors commutated by Pulse Width Modulation (PWM) inside the converters. Thus, power converters, to comply with the distortion limits, are equipped with filters, and control methodologies are even required for the compensation of power unbalance. In this paper, the main goal is the quantification of the impact of harmonic distortion on the unbalance. After the presentation of a theoretical approach to deal with harmonic distortion and unbalance by appropriate indicators, a PV system with multi-inverter configuration is tested. The measurements of power quality of the worst and the best converters are compared to the overall measurements of power quality for all the inverters.