Reliability and losses investigation of photovoltaic power generators during partial shading

Abstract

Photovoltaic (PV) generators are the major power generation units of a PV system comprising of modules connected to the interfacing devices i.e. solar inverters. The generators are mainly named based on the type of interfacing devices i.e. series string (string inverters), parallel short strings (central inverters) and multi-strings (multi-string inverters). However, the generators are highly vulnerable and sensitive to the partial shading that results in overall system performance deterioration. In this paper, the reliability of these PV power generators is evaluated under various static and dynamic shading scenarios using MATLAB/Simulink and real-time prototype. The performance of the generators are studied in term of the power generation, mismatch and power losses, losses due to false tracking by the maximum power point tracker (MPPT), efficiency and power-voltage (P ~ V) curves analysis. The conducted analysis shows that during 25% system shading, all the PV generators have encountered nearly equal power losses of 50% whereas with increasing the shading to 50%, the multi-string generator has excelled in performance with lower power loss (63.31%) as compared to the series string and short parallel strings generators experiencing 70% power losses. Also, the series string encountered a severe power loss of 87.98% during 75% system shading as compared to parallel short and multi strings generators (76%). During dynamic shading scenarios the multi-strings generator generated the higher power as compared to others and hence can be adopted in PV plants to reduce power loss due to shading. However, the long string and parallel strings connected via single solar inverter for transferring power to the electrical grid should be avoided to reduce unexpected power loss due to shading.