Degradation detection of PV arrays using extremum-seeking control based MPPT

The system operating costs and long-term reliability of the PV modules is significant in reducing the total lifetime cost of the PV system. In this context the diagnostic methods in identifying the degradation affecting PV array is important. Previous studies on degradation in PV modules showed that degradation leads to either decrease in shunt resistance or increase in series resistance of the PV module. With change in internal resistance of a PV array, the transient characteristics of array quantities (array voltage and current) may change. The effect of internal resistance of a PV array on transient characteristics was studied in this brief from the small signal model for a PV system with boost converter. The step responses for studying transient characteristics was obtained by implementing an extremum seeking control (ESC) based MPPT which injects a square wave dither signal into the duty ratio signal. The transient characteristics of array voltage signal were analyzed using suitable integral performance indices which helps in detecting degradation of PV array.