New monitoring method to characterize individual modules in large photovoltaic systems

Abstract

Photovoltaic (PV) systems power losses are approximately 15-20% of the performance ratio for current PV systems. There are several reasons that explain PV modules failures, and since they are connected in series to the rest of the string, a failure in one module may result in losses in the entire string. In addition, some of these failures, if are not fixed in time may become permanent and may reduce the lifespan of the PV modules. Periodic monitoring is the only way to detect these failures. Monitoring techniques oriented to groups of modules are unable to detect faults in individual modules. I-V curve tracers, which are oriented to module level and use power electronics components and large capacitors, require to disconnect the PV module from the rest of the system and long measurement times. This works proposes a methodology, that is able to take partial measurements of individual PV modules and recompose their characteristics with only small capacitors in the range of tens of microfarads and without power electronics components. The monitoring methodology is able to measure individual PV modules without modifying the electrical interconnection circuit and to deviate the operating point to +/-0.3 A and 5 V in less than 5 ms. From this deviation, the system recomposes the PV module I-V characteristics with accuracies that are between 1 and 3% for the region close to maximum power.