Power conversion in concentrating photovoltaic systems: Central, string, and micro-inverters

In this paper, concentrating photovoltaic (CPV) systems coupled with various inverter configurations are modeled, compared, and tested. Because CPV systems use optics to concentrate sunlight onto highly efficient PV cells, the systems are affected not only by mismatches in the I-V characteristics among individual PV cells but also by the electro-optical mismatches of each concentrator. The best way to minimize power losses by these mismatches is having higher quality controls in aligning at the time of manufacturing and installation. To mitigate the power losses when mismatches are present, electrical components can be considered at the expense of additional cost. The developed models for central, string, and micro-inverters allow an accurate estimation of power losses in CPV systems and can be used to find an optimum solution for various power conversion schemes on the basis of the given mismatch conditions. Simulation results show that a CPV system with micro-inverters outperforms a CPV system with conventional inverters. Experimental test results under normal operation validate that power losses in a CPV system can be reduced by more than 5% by using the micro-inverter scheme.